3 Humans in the hot deserts and subdeserts. (2024)

1. Human settlement of the hot deserts and subdeserts

1.1 Technological and social adaptations to a difficult environment

The scarcity of resources in the hot deserts and, to a lesserextent, in the hot subdeserts has forced most humans living there tolead a nomadic life. Over the centuries, different human populationshave survived in arid lands by making use of what is offered by theirenvironment and by learning to organize their seasonal transhumance soas to anticipate the seasonal changes.

Thus, they have traveled to sites where there was food and waterfor them and their herds, taking advantage of the abundant water in therainy season and staying near poorer but safer permanent sources ofwater in times of scarcity and drought. Sedentary populations have onlyoccurred where water was not a limiting factor, for instance, at anoases or on the banks of some large rivers bearing water that fell asrain in distant mountains.

Sedentary life and the control of water resources

Many deserts have not always been as dry as they are today. TheSahara, now the textbook example of a hot desert, was very dry at thepeak of the last glaciation (about 18,000 years ago), but the melting ofthe glaciers made it a very rainy region (though there continued to be adry season) with large lakes. The deserts of Arabia also show traces ofpast wetter periods some 9,000-6,000 years ago, when the fauna of thelakes in what are now the Rub' al-Khali and An Nafud desertsincluded hippopotamuses. Little is known about Arabia's archeologyin comparison with the Sahara's, and it is still not known for sureif any human populations lived there, although in light of known laterpopulation movements it seems likely that some did. Remains ofpre-Neolithic settlements are also very scarce in the other hot deserts(apart from those in Australia, where the Paleolithic lasted untilBritish colonization of the nineteenth and twentieth centuries).

Colonization of the deserts requires technological adaptationsbeyond the reach of the bands of Paleolithic hunter-gatherers, whopreferred to live in less inhospitable areas anyway. In fact,hunter-gatherers have, in almost all cases, only colonized deserts andsubdeserts when more powerful and aggressive populations--ortechnologically more advanced ones--have forced them to take refuge inlands unsuitable for agriculture; this is true of the San of the desertsof southern Africa. Most of the world's hot deserts (except thosein Australia) were really only colonized when irrigation-basedagriculture and nomadic pastoralism developed.

Irrigating crops and traveling with herds in search of pastureshelp make food supplies more regular in harsh arid environments, and theoldest (and almost contemporary) traces of both techniques seem to comefrom the same region: the northern desert and subdesert areas of theSyrian Desert and Mesopotamia adjacent to the Fertile Crescent. In thisarea, about 8,000 years ago, some human groups were experimenting withirrigation by gravity using water from artesian springs, while othersstarted to travel across the deserts with their herds in search ofgrazing. Since then, these two economic and social systems have been putto the test, either complementing each other or ending up asirreconcilable opponents.

Irrigation for agriculture started to take off in Mesopotamia7,000-8,000 years ago, in Egypt about 6,500 years ago, and in the IndusValley roughly 6,000 years ago. Irrigation provided the basis for thefirst great historical civilizations and the first city-states in whichpower was centralized and a significant part of the population heldposts that were not related to food production (jobs in administration,warfare, manufacturing, sciences, or the arts).

Not all traditional irrigation-based agriculture has utilizedsurface or underground water. Some desert farming cultures have beenbased on the use of rainfall. The Nabataeans and the Peruvians developedelaborate, but different, techniques to make use of the slightestrainfall.

Between 400-200 b.c., the powerful Nabataean kingdom occupied theSyrian Desert as far as the Negev, along the eastern bank of the Jordanand the Dead Sea. They prepared a reasonably large water catchment basin(about 20 ha for each hectare [1 ha=2.5 acres] to be irrigated) andchanneled the rain falling anywhere in the basin to the plots theywanted to irrigate. This was an area of 1-3 ha, at the outlet of thecatchment basin with a margin that acted as a dam to retain the topsoiland the incoming water. The water permeated into the soil and suppliedthe soil water reserve. If there was any water leftover (after heavyrainfall), it could flow to the next plot at a lower level and then toothers at even lower levels. Less is known about the techniques used bythe ancient coastal inhabitants of Peru, but they certainly includedterrace systems and systems to use rainwater. In the Arequipa region,the recurrent fog at the altitude of the lomas seems to have been usedin a sort of dry farming that did not rely on rain.

Irrigation agriculture is now widespread in all the world'sarid and semiarid regions, even in the Mediterranean areas (see vol. 5,pp. 275-279), but nowhere is irrigation as important for humansettlement as in the hot deserts. Irrigated areas create concentrationsof high population density in a small area. Most humans living in hotdeserts--in Mesopotamia, the Peruvian coastline, the Nile Valley, theColorado Valley, the Saharan oases, and the villages of the ChihuahuaDesert--in fact live outside the desert in areas that irrigation hastransformed into market gardens and orchards

Nomadic life and control of routes through the desert

The strategy of extensive exploitation of both water and grazingresources in the immense hot desert lands seems to have originated inthe deserts of southwestern Asia at almost the same time as irrigatedagriculture. Contemporary Bedouins are probably the direct descendantsof those first nomadic herders of about 8,000 years ago, whose lifestylemust have been very different, as the ass or camel had not beendomesticated and horses were unknown until they arrived in the areaalready domesticated.

The first nomadic herders thus traveled on foot with their herdsfrom water hole to water hole, just as the desert hunter-gatherers haddone before them--and just as some Australian Aborigine peoples (such asthe Pilbarras) continued doing until the twentieth century. Later, somestarted to ride cows, as shown in many Saharan rock paintings from thecattle phase; cow riding was still practiced in the early twentiethcentury by Khoikhoi herders in southern Africa. The decisive step wasthe domestication of the camel, "the ship of the desert," bythe Arabs 5,000-6,000 years ago and the subsequent development of thefirst caravan routes from Syria and Mesopotamia to Egypt and southernArabia.

The nomads of the hot deserts have not always confined themselvesto extensive stockraising. Once they had beasts of burden and animals toride, the nomads also controlled the routes crossing the deserts.Nomadic trading was a natural complement to the economy of the sedentaryinhabitants of the oases: the nomadic herders supplied the sedentarypopulations with livestock products (wool, leather, milk products,horns) and could transport their goods reliably across the desert. Inturn, the sedentary peoples supplied the nomads with plant foodstuffsand all the manufactured objects necessary for life in the desert(knives, textiles, cooking utensils, and weapons). Sometimes, thiscomplementary relationship soured, leading to confrontation andhostility. It is important to note that the two sides have deepdifferences in their social organization and outlook. Nomads have beenstereotyped as barbarous, violent, dangerous people with unlimitedterritorial ambitions, troublemakers who are envious of the good lifeenjoyed by people who have settled down. Sedentary peoples have beenstereotyped as greedy tricksters, jealous of the nomads' freedomand lacking in both strength and resolve.

Individual ownership of land makes no sense to the nomads of thedeserts of Africa and Asia; for them, personal wealth takes the form oflivestock, slaves, servants, and easily transportable valuable objects(jewels, decorations for tents, harnesses, weapons, clothing). Pasturesand water holes, however, are the collective property of the differentgroups of each nomadic society and sometimes give rise to disputesbetween them, disputes that often end in bloodshed. Violence andaggression, together with an overriding sense of honor, can set off achain of killings and revenge killings between families and clans. Thisaggression, when directed outward and exercised collectively by a largeenough group of nomads, may turn a minor quarrel with the sedentarypopulation of an oasis into a series of attacks on caravans withpillaging, slaughters, the imposition of tributes, or even an outrightwar (which the nomads have always tended to win, as they are betterprepared for combat).

The crisis arising from the spatial and functional division ofresource usage

In the end, the fascination of the cities has historicallyconquered the nomads, or at least their leaders, who have settled incities and eventually adopted a sedentary lifestyle. The cities of thedesert have always been surrounded by legends, intense fascination, andeven religious worship. Islam was born in Medina, though it needed thehelp of the Bedouins to conquer Mecca and to begin the irresistibleexpansion of the first centuries of the Hegira. Islam made its cities oforigin into centers of pilgrimage and developed a civilization in whichcities from Cordoba to Delhi and from Timbuktu to Samarkand were thecenters of power and the creation and diffusion of culture. Cities, asfourteenth-century Arab philosopher, historian, and sociologist IbnKhaldun (1332-1406) commented, have been the necessary condition forcivilization; wherever it has taken root, Islamic civilization hastransported the city model based on Mecca and Medina.

Ibn Khaldun was highly critical of nomads, especially Bedouins, andpointed out that when nomads conquered a city, their leaders initiallymaintained their nomadic identity and remained in close contact withtheir warriors. Local authorities were responsible for all aspects ofcivil administration. Later, however, the nomad leaders integrated intothe old sedentary aristocracy and adopted their values, so the nomadstate became sedentary and urban.

Throughout the twentieth century, the implantation of a system ofnation-states throughout the Old World hot deserts has completelychanged the relationship between nomads and sedentary peoples. (It seemsto have tipped the balance even further in favor of the latter.) Thestates--even those ruled by a dynasty with nomadic origins (SaudiArabia, Jordan, Kuwait) and those mainly controlled by peoples from anomadic tradition (Mauritania, Libya)--sooner or later (and generallysooner rather than later) become sedentary; the city-dwellers inevitablyseek to preserve their sovereignty, expressed by maintaining theintegrity of their frontiers. This leads to the establishment ofpolicies to encourage permanent settlement, the construction of newcapital cities from scratch, and ongoing conflicts between many nomads(especially the Tuaregs) and the governments of the states where theylive because of the incompatibility of their system of use of space withthe frontiers imposed by colonization. The nomads who do not acceptsettlement tend to be marginalized by their new society, but those whosettle down are also in marginal situations, especially if they practiceagriculture; those who respond best to this change are those whoseactivities are more in line with their cultural tradition (soldiers,haulers, traders, and the like).

The discovery and exploitation of oil fields has completed thetotal change in the socioeconomic relationships of all thepopulations--both nomadic and sedentary--in oil-producing countries.Involvement in oil production stimulates widespread migration to thecities and oilfields and results in the abandonment of traditionaleconomic activities. Conversely, the Saharan countries where no oil hasbeen found are among the countries with the world's lowest percapita income and where a high percentage of the population is employedin traditional economic activities.

1.2 Humans in the hot North African deserts

Humans settled the Sahara long ago (see vol. 3, pp. 250-252). Whatis now an immense desert must have had a higher population in ancienttimes, when the prevailing climate was much wetter and supported aricher flora and fauna. There was, then, a wider range of resources whenhuman groups arrived in this now-desert zone either from theMediterranean coastline or from the southern savannahs.

The ancient settlers of the Sahara

The first settlers were hunter-gatherer peoples living inrelatively permanent settlements near the banks of lakes, where therewas plentiful food and water, or in the rainier strip to the south. Theoldest archeological deposits yet found (estimated to be 10,500 yearsold) show the existence of encampments inhabited by fishermen (fishhooksmade of shell have been found) and hunters of hippopotamuses andcrocodiles. The people also collected grain from the wild grasses. Sitesdating back 9,000 years have yielded evidence of the use of pottery madewith barbel bones and decorated with wavy lines. Such finds indicatethat the settlements were by this time more stable, though they did nothave a Neolithic economy. The distribution of the pottery coincidesclosely with the current distribution of the languages of theNilotic-Saharan family. Individuals who speak these languages arethought to be descendants of the groups of Saharan fishermen who made upthe aqualithic culture.

The first traces of the domestication of cattle appeared about8,500 years ago, and, within 500 years of that, some farmers werecultivating sorghum and millet. As the region's climate becamedrier, the people retreated to the oases in the Sudan, the Nile Valley,and the desert's northern and southern edges, except for thestockraisers, some of whom continued entering the desert during therainy season with their herds, beasts of burden, and steeds. About 2,000years later, desert herders could still find fodder for their horses,but horses were eventually replaced by dromedaries.

One of the greatest civilizations of antiquity, the ancientEgyptian civilization, arose about 6,500 years ago in the Nile Valleyand Nile Delta and lasted until the time of the Romans. Egyptiancivilization was based on agricultural irrigation methods that used theNile's floodwaters to fertilize the land as well as irrigate it.The flooding of the Nile is highly regular, always occurring at the endof summer. This regularity allowed the Egyptians to develop a calendarsystem and made planning for the future easier. Once the waters hadreturned to their normal level, the Egyptian farmers planted grain; thecrops grew without needing additional water until the harvest inApril-May. After harvesting the grain, the fields were left fallow for afew months, until the following flood brought new water and nutrients(see vol. 10, p. 424). The period of the Roman empire, the advent ofChristianity, and the later conversion to Islam hardly modified theliving conditions of the Egyptian farmers, though each invasion broughtnew crop species.

The Tuaregs and other current inhabitants

The Tuaregs, a Berber-speaking people, are nomadic herders.Specialized in trans-Saharan trade, they have traditionally raisedcamels and asses for use as beasts of burden on their long journeys.They also raise sheep, goats, and cows in the Sahel-Sudan region. In therainy season, they usually head toward the interior of the Sahara tofind good grazing for their herds; at this time of year, the very richmilk is the herders' basic foodstuff. Different Tuareg groups oftencoincide in the grazing areas, and intertribal events are held--thenaming of newborn children, camel dances, and weddings among them. It isalso the time when wild millet is collected and stored for the dryseason. When the dry season arrives, the Tuaregs return south, wherethey remain until the rains are due and it is once again time to set offinto the desert. If the rains do not arrive on time, many of theircattle may die.

The Tuaregs' good technical and social adaptations to theharsh conditions of the desert have allowed them to maintain their ownlanguage (Tamashek) and script (Tifinagh) despite the adversecirc*mstances. Tamashek is a language of the Afro-Asian family thatbelongs to the now highly fragmented group of Berber languages spoken inthe Maghreb (see vol. 5, pp. 186-187) and much of the Sahara.

The traditional Tuareg society is so highly stratified that one cantalk of the existence of castes or social strata. The highest caste isrepresented by the immagaren or nobles, who avoid mixing with themembers of the other strata and whose genes have thus been relativelyisolated. The imraud are vassals owing allegiance to one of the noblefamilies, but they can own slaves. The iklan, or servants, aredescendants of slaves taken prisoner on raids against sedentary farmersand kept in the service of a lord from one of the higher castes. Theinadan or blacksmith class are craftsmen who make weapons and jewelryand are usually avoided by the rest of the population. (They areconsidered dangerous due to their relationship with the supernaturalthrough the use of fire.)

Finally, there is the caste of inislimen or wandering priests, whosupply amulets to all the different strata within the groups. TheTuaregs are Muslims but retain many pre-Islamic traditions; for example,unlike Arabs and Bedouins, their society is matrilineal and they aremonogamous. Much of their social organization was broken down by Frenchcolonization and later by the socioeconomic policies of the states wherethey live, especially by the abolition of slavery and of feudal systemsof allegiance. There are now about one and a half million Tuaregs livingin the five African states in the region, Algeria, Burkina Faso, Libya,Mali, and Niger. Since these states' independence, the Tuaregs havebeen increasingly marginalized and have been in permanent conflict withthe always distant and often authoritarian governments of the newstates. The drawing up of frontiers has restricted their movements andhas been one of the main causes of conflict with the governments.Freedom of movement is essential for the Tuaregs, even though they areable to find alternative solutions to the irregularity of the climate.

To the west of the Tuaregs, in the Saharan areas of Algeria,Mauritania, and the Western Sahara, live the Moors, who are also ofBerber origin, but with greater Arabic and Islamic influences. They arealso mainly nomadic herders, although their social organization is notso stratified and as a result of their conflict with Morocco has becomeeven more egalitarian among the Reguibat and other tribes of WesternSahara, now better known as Saharans. Farther east, in Chad and Sudan,there are populations who speak Nilotic-Saharan languages, especiallythe Tedes or Tebus, the Daza, Zaghawa, Messalits, and Nubians. TheSaharan populations of Egypt, Libya, and Sudan are mostly Arabicized,though it seems that the sedentary rural populations of the Nile Valleyhave not received external genetic inputs since the stabilizationthrough unification of Upper Egypt and Lower Egypt in the times of thepharaohs.

In the Horn of Africa, the Saho, Afar, and Somali are mainlynomadic herders of goats, sheep, and camels, though there are some areaswith sedentary populations along the rivers, especially in southernSomalia and in the former city-states on the coastline. In the less dryregions of northwestern and southern Somalia and southern Ethiopia, somepeople live as stockraisers--the Boran of southern Ethiopia, forexample. They do not have as highly a developed caste system as theTuaregs, but some craft trades (such as blacksmiths and tanners, who arealso hunters) are associated with highly inbred castes. With fewexceptions, all these peoples of the Horn of Africa are repelled by theidea of eating fish; even on the coast, only the nonnative populationeats fish. Only a few groups of Somalis, among them the Midjurtin at theeastern tip of Somalia and the Rer Magno on the coast north of Moqdiisho(Mogadishu), are mainly fishers.

1.3 The humans of the hot deserts of southern Africa

The deserts and subdeserts of southern Africa are inhabited mainlyby populations that have settled there relatively recently and who wereoften forced there by hostile peoples. The first human settlers, at anunknown date, lived by hunting and gathering roots and fruits (exceptfor those living on the coast, who collected marine molluscs) andsheltered in caves. Nowadays, the most characteristic inhabitants arethe Khoisan, whose morphology and languages are sharply different fromthose of all other Africans, but there are also Bantu-speaking peoplessuch as the Herero and Himba.

The Khoisan peoples

The Khoisan live in the deserts, subdeserts, and savannahs ofsouthern Africa (Botswana, Zimbabwe, Namib-ia, and South Africa). Untilrecently, the roughly 55,000 San, or Bushmen, lived in the dry savannahsand the subdesert thickets of the Kalahari as hunter-gatherers, but veryfew now live their ancestral lifestyle.

The roughly 30,000 Khoikhoin, or Hottentots, are nomadic herderswho breed herds of cattle, sheep, and goats; the milk of these animalsis their basic foodstuff. Both groups speak variants of the Khoisanlinguistic family, the "click languages" that are the onlylanguages using unusual aspirated velar sounds known as clicks. Both theSan and the Khoikhoin are descended from an ancestral group thatoccupied vast areas of Africa in the past. The invasion of the Bantupeoples from the north, starting about 2,000 years ago, pushed themfarther south, and then the expansion of the European population afterthe founding of the Cape Colony 300 years ago gradually deprived them ofthe best grazing grounds in southern Africa. The Bantu and the Europeansdrove them to the most arid regions of southern Africa, where they stilllive, as they could not defend themselves from the Bantu people'ssuperior iron tools and weapons or the Europeans' firearms. Theconfrontation of the Khoisan with the invaders led to the exterminationof some (such as those who used to live in the area of the Cape of GoodHope), the enslavement of others (such as the Nusan, servants of theTswana, the majority Bantu tribe in Botswana), or marginalization (the!Kung of Botswana and Namibia). Many were recruited by whites to work inmines, in agricultural and stockraising installations in South Africa,and more recently as guides for the South African Army during theNamibian independence war.

The Khoisan are short; their average height is 5 ft (1.6 m). Oneunusual characteristic of these peoples is steatopygia in the women--thetendency to accumulate fat reserves on the buttocks and thighs withoutdeveloping generalized obesity in the rest of the body. It starts todevelop at puberty, increases with age and successive pregnancies, andis accentuated by the highly curved lower spine of Khoisan women. It hasbeen suggested that steatopygia is a physical adaptation to dryenvironments--a molecular water reserve. Yet the Khoisan only occupiedthese environments recently, and some of the rock paintings by theirancestors, found in wetter or formerly wetter regions from the Sahara tosouthern Africa, already show this feature. Sexual selection is anotherpossible explanation for steatopygia, because in these societies largebuttocks are a highly valued female characteristic.

Two additional morphological characteristics further distinguishthe Khoisan from other native populations in southern Africa: theirepicanthic fold (a fold of skin on the inner angle of the upper eyelid)and light skin pigmentation. The epicanthic fold makes the Khoisan lookrather Asian and led early anthropologists to consider a hypotheticalAsian origin, but this is now rejected. Their light skin coloring leavesthe Khoisan at risk of sunburn after excessive exposure to the sun. Thisinsufficient pigmentation seems to confirm that the Khoisan have notoccupied the desert environment until the last few centuries and evolvedin conditions of less intense sunshine in the temperate regions of thesouthern tip of Africa or even in regions now occupied by the Saharabefore they dried out over the last few millennia.

The Bantu peoples

The earliest remains suggesting human occupation of the NamibDesert are about 2,000 years old. At that point in time, nomadicstockraising was already established in the area. The Zemba orHimba--"the ochre people of the dry river beds," one of thepeoples of the Herero group--say they are the descendants of those firstinhabitants. The area is also inhabited by other peoples of the Hererogroup, who belong to the Bantu tradition. The Himba are experienced inusing the desert's resources and follow a semi-nomadic strategy.They are governed by the principle of double descent, which is found infew other areas of the world and consists of membership in two clans,the patriarchal and the matriarchal: they are said to inherit spiritualand social goods from their father, and material goods from the motherand her brothers. Now independent, Namibia is forcing the Himba toabandon their nomadic lifestyle and accept school education andChristianity. Modern Namibians show little interest in or respect forthe indigenous cultures. School-educated children are rejecting theancestral culture and customs, so the maintenance and future of thetraditions are not ensured.

The Herero are nomadic herders who live in the center of Namibia onthe edge of the Namib and Kalahari. Originally from regions farther tothe north, they are possibly the descendants of herders from Angola whosettled in southern Africa in the fifteenth century, and, like the otherBantu peoples, knew how to work iron. When the Germans started tocolonize Namibia in 1883, they broke up the nomadic stockraising system.This led to the outbreak of the Herero rebellion in 1893. Combatcontinued for a period of 15 years in a genuine war of exterminationthat left more than 65,000 dead. The survivors were expelled to the mostarid regions of the Kalahari or kept in virtual slavery to work on theland the colonists had appropriated.

When World War I (1914-1918) broke out, the South African Armyinvaded Namibia; the Germans surrendered in 1915. The Herero populationwas under less pressure during the South African occupation than it wasduring the period of German domination, and they were able to recoversomewhat despite successive rebellions against the new occupants, whocontrolled Namibia until its independence (1990). The Herero now numberabout 400,000, making them one of the most influential minorities inNamibia, where they occupy numerous secondary positions in theadministration. Their traditions, however, have been lost.

European colonists

The successive waves of colonization by Germans (1883-1915) andAfrikaaners (1915-1990) left about 80,000 whites in Namibia, more thanhalf of Afrikaans origin and almost one-third of German origin. Theyrepresent only about 6.4% of the population, but they are extremelyinfluential. The Afrikaaners are more numerous in the South AfricanKaroo and in the rest of South Africa.

1.4 Humans in the hot deserts of Asia

The desert and subdesert zones of the Near East were settled byhumans during the Paleolithic, and this important crossroads has beenthe site of some of the defining events in human history. The northwestedge of the Asian hot deserts, the Fertile Crescent, saw the beginningof the change from a Paleolithic hunter-gatherer economy to a Neolithiceconomy based on domesticated animals and plants and voluntary foodproduction. Recent hypotheses suggest that the Neolithic was spreadabout 10,000 years ago by separate migrations northwest to Europe,southwest to Arabia and Africa, and southeast to Iran and India. Thesemigrants were the origin of the populations that would later speakIndo-European, Afro-Asiatic, and Dravidian languages. Two culturaltraditions started in the regions of the Syrian Desert closest to theFertile Crescent: one linked to irrigated agriculture in oases and onriverbanks, and one linked to nomadic pastoralism. These two traditionshave shaped human life in deserts for the last 8,000 years.

The hydraulic civilizations and the nomadic herders

The alluvial plains of Mesopotamia, though their climaticconditions are comparable to those of the neighboring deserts, receivewater in rivers coming from rainier regions. These plains were thebirthplace of irrigated agriculture, the basis for the appearance of thefirst urban cultures. From 8,000-6,000 years ago, many city-statesarose, first in Lower Mesopotamia, then in Upper Mesopotamia and on theplains at the base of the Zagros Mountains, and then in the widersurrounding area. The wealth of the Mesopotamian city-states boosted therise of other regional powers, which, in turn, left the subdesertperiphery or the desert itself in an effort to take over thecity-states. The Akkadian empire was populated by a Mesopotamian peoplespeaking a Semitic language. These people were the first to unifyMesopotamia and start expansion towards Syria, Anatolia, and Iran around2350 b.c. The Akkadian empire fell to the Elamites, aProto-Dravidic-speaking people whose capital was Susa (now in theKhuzistan region of Iran). Two centuries later, the Elamites werereplaced by the Amorites, marking the first expansion of the nomadicSemitic-speaking populations from the north of the Arabian desert.

About 4,000 years ago, a new hydraulic culture emerged in the IndusValley--the Harappan culture (or Indus Valley civilization), whichappears to have lasted until 3,7503,500 years ago, probably coincidingwith the invasion of the Indo-Europeans. (Some authors, however, suggestthat the decline of these civilizations can be explained by naturalcauses such as climate change, changes in the course of rivers, or themassive salinization of irrigated lands as a result of insufficientdrainage.) The Harappan culture left far fewer remains than those ofEgypt and Mesopotamia but appears to have reached a similar technicallevel. It disappeared 3,000-3,500 years ago, possibly due to climaticcauses or due to the military superiority of the Indo-Europeans who hadhorses, war chariots, and iron weapons. (Warfare would have occurredshortly before the Aryan civilization imposed its control on the wholeof northern India.)

While the Indo-Europeans were also taking control of the colddeserts and subdeserts of Iran and Anatolia, a succession of empiresarose and declined in Mesopotamia. The Babylonian dynasty (Amorite),mainly under King Hammurabi I, saw another unification about 3,800 yearsago that lasted until about 3,600 years ago. Around 1400 b.c., Assyriaemerged as the main regional power, reaching its peak from 900-700 b.c.It formed the first true empire of antiquity, as it included allMesopotamia and the Fertile Crescent, part of the interior of Anatolia,Cyprus, and Egypt. Later, the Chaldeans (Aramaeans living in Babylon)installed a short-lived dynasty that lasted less than a century, until2538 b.p., when the Persians, an Indo-European people settled in thehighlands of Iran, conquered Babylon and divided Mesopotamia into twosatraps or provinces: Assyria (Upper Mesopotamia) and Babylon (LowerMesopotamia).

Two thousand years ago, after Persian conquest and then Hellenicdomination following the conquests of Alexander the Great (see p. 384),Mesopotamia and the Arabian deserts marked the eastern frontiers of theRoman Empire. In Iran, there was a revival of the former Persian empireunder the Sassanian dynasty (the Sasanids), and, farther to the east,the Indo-Scythian Kushan empire dominated the area from middle Asia tonorthern India. The scene was totally disrupted in the third and fourthcenturies mainly by the arrival of nomadic populations from the steppesand cold deserts of Asia. The hot deserts were more influenced by Islam,which arose precisely in the Arabian deserts. In the seventh and eighthcenturies, the Muslim Arabs took their new religion west beyond thePyrenees and east as far as the Punjab, establishing the basis of anempire that was soon politically fragmented, though it showed remarkablereligious unity throughout the area under consideration (and beyond).The Mongol and Turkish invasions were the last contribution to thepopulations of the hot deserts and subdeserts of southwest Asia. In thetwentieth century, especially since the creation of Israel in 1948,Jewish immigration has led to the return to the promised land of manygroups of Jews from around the world.

All the actual populations of the hot deserts and subdeserts ofsouthwest Asia are Caucasoids and clearly differentiated from those ofnorthern and eastern Asia and from those of southern Asia and northeastIndia. They can be separated by linguistic criteria into two largegroups: the peoples speaking Indo-European languages (Baluchi, Punjabis)and those speaking Afro-Asiatic languages (Arabs, Israelis, Druze,Yemeni).

The Indo-European peoples

The deserts and subdeserts of the Near East are home to manypeoples (Baluchi, Punjabis) who speak Indo-European languages. Theyoccupy the easternmost part of this desert and subdesert area and aremainly descendants of settlers who arrived from the steppes and thecentral Asian steppes and subdeserts about 3,500 years ago.

The Baluchi form the core of the population of Baluchistan, nowsplit between Iran and Pakistan, and have interbred with the neighboringpopulations: Punjabis and Sindh to the east; Turks to the north; Arabsto the south; and Farsi to the west, though they consider themselvesdescendants of Arab populations from Aleppo. The medieval invasions byTurks and Mongols forced them to retire to the desert zones, both thehot deserts (the coastal regions) and the cold deserts (the plateaus)where they became nomads, expert horse trainers, and camel drivers.

The Punjabis and Sindhi form most of the population of Pakistan andare also numerous in India. (The Punjab was divided in two at theIndia-Pakistan frontier when the two countries became independent in1947.) Other populations of Indo-European origin also form the majorityof the population in the desert and subdesert regions of Gujarat(Gujaratis) and Rajasthan (Marwaris).

The Semitic or Afro-Asiatic populations

The peoples who speak Afro-Asiatic languages (traditionally knownas Semitic languages) seem to have arisen in the hot deserts andsubdeserts of Asia, either in the southern branch of the FertileCrescent or on the northern periphery of the deserts of Arabia.Afro-Asiatic languages are now spoken from Mesopotamia and Arabia to theAtlantic coastline of the Sahara and as far south as the equator ineastern Africa. The distribution of this linguistic family has variedlittle over time, though the relative importance of its differentlanguages has changed. Languages thousands of years old that were spokenby the populations of large empires have disappeared (such as AncientEgyptian and Akkadian), while others that were originally spoken by afew small tribes have become major world languages (for example,Arabic). Some of the languages of this family were among the first toleave written traces; the alphabet used to write this book is derivedfrom the Phoenician alphabet. Afro-Asiatic languages are spoken by theHebrews, Copts, Arabs, Berbers, Ethiopians, and other peoples.

Like the Sahara, the Arabian Peninsula had a more benign climateafter the last ice age, though both are now total deserts. Theincreasingly dry climate caused major migrations northward to morewelcoming sites, especially toward Mesopotamia. The successive waves ofmigration were by Akkadians (5,000 years ago), Amorites (4,000 yearsago), Aramaeans (about 3,000 years ago), and Arabs (in the seventhcentury). Roughly 3,000-4,000 years ago, the Hebrews and Canaanitessettled in the area of Palestine and Syria.

The term Arab is used to designate all the inhabitants of theArabian Peninsula, but it is necessary to distinguish the inhabitants ofsouthern Arabia (or Arabia Felix), who are mainly urban and sedentarywith an agriculture-based economy, from the inhabitants of central andnorthern Arabia, who are mainly nomadic herders, although there are alsosedentary farmers, known as fellah, in the oases. The origin of the Arabnomads goes back 3,000 years. When the domestication of the dromedaryand the techniques related to its use as a beast of burden or as a steedbecame widespread in the Arabian desert, the peoples living in the northof the peninsula (Edomites and Nabataeans) could travel and colonize thedesert region (the Nabataeans excelled in their low-water-consumptionirrigation and agricultural techniques). They soon controlled tradebetween Arabia Felix and Mesopotamia. The Assyrians knew of thesewarrior peoples around 2,850 years ago. By about 2,000 years ago, theArab herders had reached Arabia Felix and had assimilated the groups ofhunters that still lived there, establishing castes that still exist andpushing south the pre-Bedouin tribes of herders, who spoke non-ArabicSemitic languages. Arabia was reached first by Judaism and then byChristianity, and some Arabs converted to these faiths, but the typicalreligion of the Arabs is Islam, preached by the Prophet Muhammad afterhis divine revelation, which is recorded in the holy book of Islam, theKoran.

Muhammad's Islam spread very quickly, and within a centuryIslam stretched from the Iberian Peninsula to central Asia, creating acorridor with a common language, along which merchandise and culturecould circulate freely from the Atlantic to China. After 623 a.d., thehistory of the Arab peoples is inseparable from that of their religion,which, in turn, is inseparable from the history of their language. Thetrue Arabs, who claim to be the direct descendants of the Arabs of thetimes of the Koran, are Bedouins. They represent all the camel-ridingtribes of Arabia (and some areas of northern Africa). These groups arenow mainly sedentary, but some are still nomads who live by stockraisingand trade or form units in the region's armies, just like thewarriors in the past who ensured the security of the sedentary Arabs inreturn for tributes. The conversion of the Near East to Islam spread theArabic language throughout the region; thus the Palestinians and theDruze are also Arabic-speaking groups.

An Old Testament tale states that about 4,000 years ago, Abraham,the patriarch of several seminomadic tribes, led his people from Ur tothe Land of Canaan, east of the Dead Sea, in search of better pasturefor their herds. Later, possibly forced by the Hyksos, most migrated toEgypt, where they remained until Moses organized their return during thereign of Rameses II. On their way back, they spent 40 years in thedesert of the Sinai Peninsula, living as seminomadic herders. When theyreturned to their land, they had to struggle with the people who livedthere. Then they formed a confederation of seminomadic tribes, united bytheir common faith in Jehovah and commanded by temporary leaders knownas judges. They survived conflicts with the different neighboringpeoples (Canaanites, Moabites, Ammonites, and Philistines). Thepersistent threat from the Philistines led them, about 3,000 years ago,to adopt a monarchic system, which reached its greatest splendor in thedays of King David and his son Solomon.

The fall of Jerusalem to the Babylonians in 586 b.c. led to thefirst diaspora of the Hebrews, which lasted for less than a century.Their social and religious links, together with the Jews' faiththat they were the chosen people of God, has helped them to maintaintheir identity as a people, despite the migrations and persecutions(though the destruction of Jerusalem by the Romans in 70 a.d. and thebanishment of the Jews from their land led to their spread throughoutthe world for 2,000 years). In the late nineteenth century, the Zionistmovement arose and sought the Jews' return to the land of Israel.Throughout the years preceding and following the Nazi Holocaust in WorldWar II (1939-1945), during which roughly six million Jews died, tens ofthousands of Jews arrived in Palestine and demanded the creation of anindependent Jewish state there. (At the time, Palestine was underBritish administration.) The Jewish state came into existence on May 14,1948, a few hours before the end of the British occupation of Palestine,with the approval of the United Nations Organization. The firstArab-Israeli War started immediately, leading to defeat for the Arabsand the exodus of nearly a million people of Arabic descent. Fourmillion Jews and nearly a million Arabs now live in Israel.

1.5 The humans of the hot Australian deserts

It is widely accepted that humans arrived in Australia60,000-50,000 years ago, but there is no proof that they lived in thedesert until 20,000 years ago; the oldest archeological remains aresites in the Cleland Hills in the Hamersley Range and in the NullarborPlain in the south of the Victoria Desert. The zone, which must alsohave been arid then, supported a human population that lived ashunter-gatherers.

The Aborigine population

At the height of the last glaciation (20,000-16,000 years ago),humans seem to have abandoned the Australian deserts and did not returnuntil about 10,000 years ago. By the time of the arrival of the Europeancolonists, the Australian Aborigines had acquired a great deal ofinformation about the climate, plants, and animals of the areas wherethey lived. The flowering of the Grevillea trees indicated that thekangaroos were fat enough to be hunted, and the fruiting of Eremophila(emu bush) indicated that the emu would soon arrive at the water holesto drink. The rains provided the Australian Aborigines with differentand more varied foodstuffs such as flowers, seeds, and insect larvae.Like other hunter-gatherer groups, they did not store foodstuffs butrather led a hand-to-mouth existence. Gathering was done by women, whosearched for insects (and their larvae and eggs), worms and slugs; rootsof the wild yam (Dioscorea); water-lily (Nymphaea stellata) seeds;purslane (Portulaca); fruits of sedge; some parts of Eucalyptus trees;and the wood, resin, roots, and flower buds of Xanthorrhoea. The menhunted emu and kangaroos. They fished with nets or bone or thornharpoons, or they encircled the fish and caught them by hand or afterstunning them with blows. There is evidence to show that they plantedgrass seeds, mainly different species of Panicum, and cuttings of someroots, especially yams. The fact that agriculture did not prosper issurely due to the lack of incentives to plant or tend plants that wouldhave been no more abundant or predictable than spontaneous ones. The lowproductivity of land in Australia has led the people living there to usethe widest variety of food resources. But, despite this wide range offood resources, many Aboriginal songs refer to hunger, an ever-presentdanger, especially in the most arid areas.

There have never been many Australian Aborigines, and they havesurely never exceeded 200,000-300,000. When British colonization beganin the late eighteenth century, they were probably split among manytribes, about 40 of them desert-dwelling. They used tools of wood,stone, bone, and occasionally even shells. They had boomerangs, but notpottery or bows and arrows. Using the hair from their own head andbeards, which they spun with spindles, they made resistant ropes, andseveral tribes had complex rules governing hair donation by groupmembers. The old men gave up the hair from their moustache and beard,and their clean-shaven head was a mark of respect.

The European colonists

Europeans arrived in Australia in the eighteenth century but didnot enter the desert areas until much later and have never been numerousexcept in the small urban centers. To learn about the interior and toexplore it, they used natives as guides. Cattle stations and populationcenters arose in the desert, some of which have grown into small urbancenters, though only Alice Springs (founded 1871), which, as its namesuggests is next to a spring, has more than 10,000 inhabitants. ManyAustralian Aborigines were attracted to urban life and decided toabandon their traditional ways of life and live in populations such asBalgo, Jiggalong, Lake Nash, Ernabella, and Papunya in the center ofAustralia, or in Wiluna, Oodnadatta, and Alice Springs.

The many problems created by their rapid urbanization-mainlyunemployment, alcoholism, and other forms of drug abuse--has led to areturn to traditional lifestyles, especially where their routes andother infrastructure have been restored. The Aboriginal Land Movement(ALM) emphasizes that the Aborigines' links to the land led toimprovements in education in communities living in deserts. The ALM isnow managed by a community committee, which employs teachers and has aright to express its opinion on the program. Thus, thousands of peoplemaintain their languages because education is bilingual. There are alsoradio and television stations controlled by Aborigines broadcasting inseveral languages to the people living in the desert. Even so, access toa suitable sanitary system is a problem for communities living in theAustralian desert. Legal conflicts often arise between Aboriginalterritorial councils and mining companies wishing to exploit theirsacred sites, but in some cases agreements have been reached thatsatisfy the Aborigines, the government, and the geological exploitationservices, since they represent work for the Aborigine community.

1.6 The humans of the hot deserts of North America

Since the first settlers crossed the Bering Strait, humanpopulation movements in the Americas have been very complex. Indifferent places and at different times, the Amerindians have formedgroups and tribes related to each other by their language or by thedifferent techniques used to extract natural resources, depending on theclimate and terrain. The high mobility of the groups and the variedcontacts between them split the indigenous population of the Americasinto a complex mosaic of neighboring tribes with widely differentdegrees of relationship. Linguistic features seem to reflect geneticrelationships more closely than cultural or geographic ones do, thoughsome groups are left out and there is no unanimity among historicallinguists. One of the more recent interpretations, that of Joseph H.Greenberg, seeks to bring together the three main families establishedby American anthropologist and linguist Edward Sapir (1884-1939) in1929; Amerindian, Na-Dene and Eskimo-Aleutian. The indigenous peoplesliving in the hot deserts and subdeserts of North America can be dividedinto three main linguistic groups: the Uto-Aztecan, North Amerindians,and Na-Dene. They all used to occupy areas much larger than the hotdeserts and subdeserts.

The Uto-Aztecan peoples of the Mojave Desert and northern Mexico

Some Uto-Aztecan speaking peoples used to occupy much of the MojaveDesert in California and much of the hot desert and subdesert land westof the Rio Grande, in the area now on the frontier between thesouthwestern United States and northern Mexico. Their survivalstrategies were very diverse: some of the more southerly groups hadlearned the agricultural techniques of the Neolithic centers ofMeso-America and lived in stable settlements, while the more northerlygroups were hunter-gatherers. The Mojave Desert-and the desert andsubdesert areas of southern California in general-was home to the mostsoutherly Paiute, whose main area of concentration was farther north, inthe Great Basin (see also p. 393). Their main tribe in this area was theChemehuevi. The desert character of the zone forced them to live aprecarious nomadic life as hunter-gatherers using a very limited rangeof tools, but they had a wide range of baskets and receptacles that theyused for very diverse purposes. They gathered roots (the reason why theyare known as "digger Indians"), herbs, and fruit and capturedfish and small game (mainly cottontails), though they also hunted biggergame (deer) when they could.

The Pima lived farther to the southeast in the Sonoran Desert. Theyformed numerous tribes that developed into a very advanced agriculturalsociety. The Pima grew maize in terraces that they irrigated withsystems of channels. They hunted small game, fished, and gathered; theyalso obtained food and alcoholic drinks from agaves and cacti. Tribalceremonies sometimes called for the ritualistic use of peyote, a smallcactus with hallucinogenic effects (see p. 192). The Pima became knownfor their skilled craftspeople who wove and dyed cotton, fashionedexcellent baskets, and made ceramics. Members of the tribe had smallChocho dogs and succeeded in domesticating hawks and eagles, fed by thechildren with snakes, lizards, and leeches. For transport, the peopleused bags made of bundles of reeds; the women used nets to carryextra-heavy loads. Their social regime was patriarchal, and the villageunit was ruled by a chief. There are now about 10,000 Pima in reservesin Arizona and about 3,000 in Mexico.

The Hokan peoples of the Lower Colorado and Baja California

The lower valley of the Colorado River and the entire BajaCalifornia Peninsula (and the coastline of the State of California asfar as San Diego) was inhabited by Hokan-speaking tribes. Those in thelower valley of the Colorado (Yuman, Mojave, Maricopa) had highlydeveloped irrigated agriculture, related to that of the neighboringPima, but they also fished with nets in the river, hunted, and collectedwild grains (grasses, which they sometimes sowed, and fruits, oftenthose of different species of mesquite). The Hokan of the Californiancoastline and Baja California (Diegueno, Cochimi) were often specializedgatherers, and there were intertribal subdivisions: the coastal groupscaught fish and collected seafood, and the inland groups did morehunting and collected plant foodstuffs.

Both were bellicose (warring) peoples who valued war as a means ofspiritual enrichment for the tribal collective and submitted to strictrule by their chiefs in times of war (which they did not do so readilyin times of peace). The social status of women was subordinate, and theyperformed much of the agricultural labor. By 1910 there were less than4,300 Hokan-speaking Indians, and many of their groups are nowpractically extinct; about 1,500 Mojave survive in reserves inCalifornia and Arizona (less than half of them still speak theirlanguage), along with about 400 Maricopa (only 100 of whom still speaktheir language) and a few representatives of other tribes.

The southern Athabascan peoples

The Athabascans (or Na-dene) tribes show clear linguisticuniformity despite their wide geographic distribution throughout Alaska,much of western Canada, and some of the states of the southwesternUnited States. The center of origin of the Athabascans seems to havebeen close to Lake Athabasca, where they arrived from Alaska, possiblyin the second wave of humans to cross the Bering Strait. However, themost culturally interesting and the best known (because of theirprolonged contact with Europeans) are the southern groups, the Apacheand Navajo, who stopped their migration in the sixteenth century whenthey came up against the Spanish. The Apache were of great historicalimportance, and the Navajo culture showed great vitality. The Navajolive in an area at an altitude and in conditions comparable to that ofthe Great Basin and, thus, the cold deserts (see p. 394). Some of theApache lived in the Chihuahua Desert, though their culture is generallymore like that of the Plains Indians.

The recent arrivals

The expansion of the Europeans meant that the Indians of the hotdeserts and subdeserts of North America came into contact with peoplewith very different customs-the Spanish colonists and missionaries.These arid regions initially attracted only hunters and trappers, laterfollowed by prospectors for gold and other valuable minerals. Colonistsalso arrived to settle there, made possible by the wealth of thesubsoil. Development, especially during the twentieth century, has beendue to this wealth, in conjunction with the expansion of irrigationsystems, industry, and tourism. Large cities have thus grown up in thehot North American deserts such as Las Vegas (Nevada) and Phoenix(Arizona). The highly-mixed native populations of the desert areas ofNorth America, which ceased to be Mexican in the mid-nineteenth centuryand became part of the United States, have maintained a strongHispano-American influence, greatly accentuated in the last few years bythe intense and largely clandestine migration into the United Statesacross the frontier formed by the Rio Grande. The heavy Chicanoinfluence is contributing to the development of a creole culture on thefrontier.

1.7 The humans of the South American hot deserts

The coastal desert regions of modern-day Peru and Chile are amongthe most important areas of Neolithic development in the Americas.Roughly 7,000-4,000 years ago, resources caught by hunting became lessimportant than the exploitation of marine resources and of plants inriver valleys.

The peoples of the Peruvian coastline

The 5,500-year-old archeological sites in Chilca and Ancon (on thecentral Peruvian coast) contain evidence of the cultivation of cotton,which was used for fishing nets as well as textiles. The bottle gourdwas also grown, and for 5,000 years bottle gourds are known to have beenused as receptacles and also as floats for fishing nets. The firstvillages, one of the most important of which was Las Haldas, wereestablished on the coast, but 4,500 years ago the settlements moved tothe river valleys, near the fertile silt of the seasonal floods. Systemsto irrigate the fields soon developed. The most important archeologicalsites are at Aspero, Sechin Alto, Huaca de los Reyes, and Garagay, wherestone and peat constructions had appeared by 2600 b.c.

Around this time, thousands of tons of earth and stone were movedto build large tumulus temples, indicating considerable technical andorganizational ability. Archeological finds from the Peruvian coastlineand plateau dated 5,000-4,000 years ago suggest the progressiveestablishment of the long-distance trade of colored seashells for tubersfrom the Andes or brightly colored feathers from Amazonia. Ceramics andthe spread of maize cultivation reached the Peruvian coastline 4,000years ago, though farther north in Colombia and on the Ecuadoriancoastline remains of pottery a thousand years older have been found. Therichest and most complex civilizations of South America (Chavin, Nazca,Moche) also arose along Peru's desert coastline and the Peruvianplateau.

The Atacaman peoples

In the Atacama Desert, a pre-Columbian culture developed thatspread to cover a vast area. The territory of the Atacaman peoplecovered the puna de Atacama (the inland high plateaus) and as far as ElHuasco and Jujuy. They were displaced from these regions by the attacksof the Diaguita and the Incas (Inca Yupanqui). Archeological sites inthe Atacama Desert show there were relations between the Andean culturesin Peru, Bolivia, and northern Chile. Contact with the Peruvians led theAtacamans to adopt agriculture and become sedentary. About 5,000 yearsago, the Chinchorro mummified the corpses of children and decorated themwith clay and paint; they buried their adults with textiles, baskets,hunting tools, and other items of significance. The San Pedro site,2,600-3,000 years old, contains ceramic pieces with similarities tothose found in Tiahuanaco, near Lake Titicaca. Finds at othernecropolises include stone tools (balls for bolas, harpoons, and tipsfor lances and arrows), wooden and bone tools, and interestinggeometrically painted pottery.

From the tenth century onward, there is evidence of the existenceof cities-Caserones (Tarapaca, Chile)-with an economy based on advancedagriculture and with fortifications and rectangular buildings thatbounded public squares and spaces. From 1480 a.d. onward, Inca influencein the region was very strong, as is clearly shown by the types ofburial.

The Atacamans are remnants of former populations that weredisplaced by later population movements into the area. They are presumedto have been related to the Diaguita and the Changos and may have had acommon origin with them. They call themselves lincan-antai (villagedwellers), or Lipas, and speak Cunza. The Atacaman people areshort-statured: the men are a little more than 5 ft (1.6 m) tall, andthe women are not quite 5 ft (about 1.45 m). They were nomadic hunterswho traded with tribes from farther north and from the interior and withthe Changos on the coast. Present-day Atacamans live by agriculture,stockraising, and fishing.

1.8 Sickness and health in the hot deserts

For a human population to exploit the resources of an environmentas hostile as the desert, it must acclimatize to the environmentalconditions. This is achieved by a series of homeostatic responses in theindividual or group. Individual responses are acclimatization, whileresponses by groups are adaptations, as they do not depend on individualplasticity but the effects of natural selection on the group.Migrations, nutrition, and general state of health contribute greatly tohelp or hinder acclimatization and adaptation.

Acclimatization phenomena

To avoid the most serious threats to humans in a hotdesert-dehydration and overheating-the body brings a series ofheat-losing (thermolytic) mechanisms into operation when temperaturesare too hot. When ambient temperatures are below 91[degrees]F(33[degrees]C), the human body radiates heat by convection. Buttemperatures are often much higher than this, and then sweating isneeded to reduce body temperature, though no sweat may be noticeable ifthe skin remains dry as a result of evaporation. However, the lost watermust be replaced in order for the body to maintain its fluid balance.The amount of water lost depends on the ambient temperature andhumidity, diet, and activity. Basal metabolism in the shade requires thereplacement of some water, the amount of which varies from individual toindividual. In sunshine, even more water is required, and if a person iswalking any distance, still more is needed. If the necessary water isnot replaced, the body is forced to draw on its tissue reserves, leadingto dehydration and thermostatic imbalance.

After the body has acclimatized, the sweat is less salty, reducingthe risk of ionic imbalance and thus the risk of cramps in the limbs andcardiovascular disturbances. It seems to take an individual about twoweeks to be able to move about and work in the desert, and fewdifferences have been found between the natives of desert areas andrecent arrivals. (Their responses were statistically similar.)

Morphological and cultural adaptations

Natural selection seems to have intervened in those cases wherebody morphology seems designed to favor heat loss. Tallness, long limbs,and scarce adipose (fat) tissue all make heat loss easier, by increasingthe surface area/volume ratio. The most frequently cited example is theNilotic peoples of the Sudan. Yet it can be argued that this body shapealso favors water loss, though this can be compensated by suitableclothing or shelter.

Clothing is important in protecting the body from sunshine. Inprinciple, the clothing worn should be loose and lightweight. If veryactive labor is required, though, it may have to be done in the nude, assweat-soaked clothing does not protect from the heat. Clothing is alsoneeded as protection against the hot desert winds. (The Tuareg and Moorsare famous for covering their faces.) These winds cause great stress andincrease the risk of dehydration, as they greatly increase the loss ofbody water. The inhabitants of the Sahara wear loose, light clothing,including turbans, and wear sandals that are about 1 in (2 cm) longerthan the soles of their feet.

Dwellings are another type of cultural adaptation. To prevent heatfrom entering homes and other structures, building materials such aspeat, mud, or stone with a high specific heat capacity are used,measures are taken to favor reflection of sunlight, and ventilation isreduced, as it would lead to the entry of hot air. The shape is usuallycompact, and many dwellings are usually built side by side to maintain asuitable microclimate. In very hot sites, underground dwellings arebuilt to keep the rooms cool, making use of the high specific heatcapacity of the ground. Desert nomads who live in tents, however, haveto ensure ventilation to cool the environment during the daytime. Thehigh specific heat capacity of the ground means they are also morecomfortable at night, when the temperature may be low in deserts.

Hunter-gatherers who do not have stable dwellings have to defendthemselves from the large temperature changes in other ways. The Khoisanof the Kalahari, for example, make fires and sleep together around themin a circle and under a blanket, with their feet near the fire, creatinga steady temperature of about 77[degrees]F (25[degrees]C). Australiandesert Aborigines can withstand frosts without stress and are notaffected when nighttime temperatures fall, even though they are naked.

Recurrent famine

Famines are by no means restricted to hot deserts, though theprecarious and unforeseeable nature of production in deserts means theyare more likely to occur there than in other richer and more predictableenvironments. Yet famines are often the result of social and politicalinequalities and an unfair distribution of wealth, not just a simpleshortage of food. Local or regional famines may be the direct result offailures in the production or distribution of foodstuffs due to naturalcatastrophes (flooding, eruptions, earthquakes, drought, frosts,epidemics, pests) or they may be seasonal and restricted to the timebefore the harvest when reserves from the previous year are finished.More often, however, they are due to social or political factors (wars,revolutions, mistaken planning, debt, corruption, speculation, orhoarding).

In reality, it is hard to establish when there is an episode ofgeneralized famine, as it usually becomes highly political, making itdifficult to ascertain the truth; sometimes it is convenient to hide badpolicies or marked social inequalities or to receive aid with the excusethat the population is going hungry. In a generalized situation offamine, there is a clear increase in mortality (in the absence of anyprevious epidemic) that mainly affects the marginal or subordinategroups, coinciding in time with a fall in the birthrate and, of course,with increases in the price of foodstuffs. The increase in the deathrate may be due to several factors: 1) malnutrition, 2) the associatedsocial disorders, due either to the lack of food or to the resultingmental disorders, or 3) the accompanying infectious diseases, asmalnourished people are more susceptible to infection by pathogenicagents.

The threshold for the clinical symptoms of hunger is a loss ofabout 10% of the body weight before an episode of starvation. Weightloss affects all body organs except the brain, but weight loss by otherorgans is unequal: the liver, intestines, and skin lose most, while thekidneys and heart lose least.

In any human group affected by famine, those who suffer most arethe most physiologically vulnerable individuals, especially children.Children are the first to show the classic symptoms of theprotein-energy deficiency diseases, kwashiorkor and marasmus.Kwashiorkor, often called infantile pellagra, is a dietary deficiencydisease, essentially a lack of protein (and not carbohydrates), thatmainly affects children 1-3 years old and usually takes the form ofanemia, edema, weight loss, and a characteristic loss of pigmentation inthe skin (which looks pellagrous). Some types of marasmus are linked tolittle or no calorie intake (often due to excessively early weaning andfeeding with excessively diluted milk powder), and the clinical symptomsare major weight loss, up to 40%, and extreme wasting of the fat andmuscle.

Malnutrition often begins even before the child is born. In areaswhere famine is endemic, the children of malnourished mothers usuallyhave a lower-than-normal weight at birth and reduced defenses that makethem easy victims to many parasitic infections. Death in childbirth iseven more common among malnourished mothers who cannot breastfeed. Evenwhen infants are breastfed, though, they start to fall victim tomalnutrition as soon as they are weaned. Malnutrition affects the growthof the central nervous system when it occurs so early in life; theearlier this occurs, the harder it is for the affected child to developcorrectly. Children suffering chronic malnutrition grow less than thosewith a normal diet, so the age/height ratio is a significant indicatorof the problem. Episodes of acute malnutrition are more clearly shown inthe weight/height ratio.

In adults, the first clinical symptoms of malnutrition areweakness, muscle pains, slow movement, nocturnal insomnia (though thereis a gradual increase in the hours of sleep), sensitivity to noise, andfragility of the skin, which is easily bruised. The blood pressure andheartbeat decline, there are episodes of diarrhea due to atrophy, aswell as digestive disorders and edema. The brain is not directlyaffected by these physiological responses, but they are associated withemotional upsets, including alternating episodes of apathy and extremeirritability. Concentration is poor, memory lapses become more common,and conversation is slower. Scalp and pubic hair is lost in both sexes;women grow hair on their face, and beard growth stops in men. Womencease menstruating and men stop producing sperm, and there is also aloss of interest in sex. Eventually, the appetite is lost altogether.The body's resistance to periods of starvation is very variable,and individuals not performing any physical activity have survived forup to two months. The loss of 40% of the body's weight is thecritical point that usually leads to fatal consequences.

There are also social responses to worsening famine. The alarmphase is characterized by hyperactivity, due to the urgency of thematter; people show solidarity, helping and assisting each other.Gradually, markets become more and more chaotic. During the secondphase, resistance, the group turns its attention to food sources thatare normally ignored or considered inedible. Social relationships becomeless frequent, visits from family and friends are considered suspicious,provisions are hidden, and food is prepared and eaten secretly. Whenweight loss among the members of a group reaches an average of 20%,serious social disturbances cease. The third phase, exhaustion, leads tothe disintegration of the family and inequality in the division offoodstuffs that had not occurred previously; food is withheld from theweakest, the old, and the young. Children are sold or abandoned, peoplemay kill for food, and there may even be cases of cannibalism.

Eye infections

The different forms of ophthalmia are inflammations of the eye,especially of the conjunctiva, the thin membrane covering the front ofthe eyeball and behind the eyelids. Granular conjunctivitis, or trachoma(also known as Egyptian ophthalmia), is an infection of the cornea andconjunctiva produced by a microorganism (Chlamydia trachomatis). It ischaracterized by marked photophobia and granular inflammations of theinner part of the eyelids, which may either heal or develop into seriouspurulent infections that cause blindness. Chlamydia infections aresexually transmitted diseases that can be transmitted from mother tochild at birth, and this is why trachoma is the most serious ophthalmiaamong newborns. Adults can also be infected in conditions of poorhygiene and high population density. It is spread by direct contact,infected clothing and water, and sexual transmission. Dry climates seemto favor the disease, and the countries with the highest rates ofinfection are in the hot deserts of northern Africa, the Near East,Australia, and several countries in the New World. But the disease isalso present at lower levels in the countries of south and southeastAsia, Russia, Japan, New Zealand (where it affects the Maoris), and thePacific Islands.

2. The use of plant resources

2.1 Harvesting without planting

Many plants growing wild in deserts can be used by humans in a widevariety of ways. Some can be used directly as shade, shelter, orfencing, while others are sources of foodstuffs or grazing forlivestock. Still others provide water, fuel, or building materials ormaterials for a huge range of articles such as arms, tools, textiles,baskets, furniture, and artistic or ornamental objects. Some wild plantsare the sources of active ingredients in various medicines, especiallypsychotropic drugs, or raw materials for industrial processes.

The desert larder

Hunter-gatherers and nomadic herders have had to rely on nativeplants to feed themselves. The seeds of wild grasses, for example, havebeen widely used to obtain flour in Australia, the Americas, Africa, andthe Near East. Unfortunately, the nutritional value of most edible wilddesert plants is unknown, though considerable efforts are now being madein South Africa and Australia to remedy this. Recent studies of thetraditional food plants of the Australian Aborigines have shown that thepods of many species of Acacia are highly nutritious, with a highcontent of protein (17-25%), fat (4-16%), and carbohydrates (30-40%).The hard impermeable seed covering means they can be stored almostindefinitely without deteriorating, making them a good food reserve fortimes of scarcity.

One of the most promising species for plantation agriculture in thewestern Sahel is Acacia colei, a recently described species formerlyincluded within A. holosericea. The edible plants of the Namib andKalahari deserts include several species of cucurbits with fruits thatare full of water: among them are the nara (Acanthosicyos horridus), aphreatophytic species that grows on dunes, the African cucumber (Cucumisafricanus), and the wild Tsama watermelon (Citrullus lanatus); C.naudinianus also stores a lot of water in its roots, while other membersof the same family--Coccinia rehmannii and Corallocar-pusbainesii--store water in their tubers.

One fruit that is of great importance in the diet of Sanhunter-gatherers is the mongongo nut, the fruit of Ricinodendronrautanenii (Euphorbiaceae). Other subdesert plants with edible fruitsinclude marula (Sclerocarya birrea subsp. birrea,Anacardiaceae), whosefruits are sometimes sold by the name marula plums; snot (Thaspesia[=Azanza] garckiana, Malvaceae); kei (Dovyalis caffra, Flacourtiaceae),whose fruit is the size and color of an apricot; Mimusops zeyheri(Sapotaceae); and Strychnos cocummoides (Loganiaceae), which, unlike thewell-known highly toxic species of the same genus, produces an innocuousand tasty fruit. The sand truffle (Terfezia pfeilii,) is also greatlyappreciated and collected for sale.

An important food for the nomadic herders of southeast Somali andOgaden is Yeheb (now spelled jicid in Somali; Cordeauxia edulis,Leguminosae-Caesalpinoideae), a little known species endemic to thearea. A small tree that reaches a height of 10 ft (3 m), it has manystems and branches, a taproot up to 10 ft (3 m) deep, and smallsecondary rhizomes near the surface. The youngest roots produce thenitrogen-fixing nodules typical of the Leguminosae. Care must be takenwhen growing it in nurseries to avoid breaking the taproot, as the plantmight die.

Jicid, formerly widespread and even locally abundant, now grows inareas with average annual rainfall of 3-8 in (85-200 mm), with sandy orloose soils, though it also tolerates slightly saline soils. It cannotwithstand flooding, but it can survive two years without rainfall; itsleaves curl up and may fall off in extreme droughts. The young treesflower and fruit after three or four years. The fruit of C. edulis takes10-14 days to ripen, after rainfall; if it does not rain, however, thefertilized ovaries can delay development until the next rains arrive.The seeds do not last for long, and they germinate rapidly, though theplant grows slowly. Jicid can also be grown from cuttings.

Jicid has an edible fruit with a shell that is easily removed.These delicious fruits, which taste similar to chestnuts, can be eatenraw, roasted, or even boiled; they might even be a good table fruit ifit were possible to establish plantations. Locally, the tree'sfruit are so important that they are often collected unripe to make sureno one else takes them. Production is about 11 lb (5 kg) per shrub peryear. The young jicid shoots and leaves are covered in numerous red orpurple scaly glands that contain 0.7-0.8% cordeauxiaquinone (the onlynaphthaquinone found in any member of the Leguminosae), a magentapigment derived from naphthazarine. This coloring agent, which rapidlyforms insoluble combinations with many metals, can be dissolved inboiling water and is used to dye some textiles (7 oz [200 g] of powderedleaves can dye almost 10 m2 of cotton fabric). This dye is also thereason why goats that browse on jicid leaves end up with patches ofbright red or orange on their teeth--and even their bones. Pigmentdeposition in the bones may directly or indirectly stimulate thehematopoietic (blood-forming) tissues to produce more red blood cells.Jicid leaves are used to make an infusion, and the liquid left afterboiling the seeds is used to make a sweet liqueur. The wood is used asfuel. The species is now being cultivated experimentally in Israel toimprove production and introduce the fruit into the food industry.

In the subdesert wastelands of northern Africa, parts of manyplants are eaten, as is a fungus, the African white truffle (Terfeziaovalispora). A starch-rich lichen (Lecanora esculenta) is eaten mainlyby livestock. The many plants eaten include the Malta mushroom (not afungus, but the parasite Cynomorium coccineum, Balanophoraceae), whichis greatly appreciated as a condiment. As in other deserts, the seeds ofwild grasses are consumed, in this case the seeds of wild millets suchas Panicum turgidum. The tender shoots of asparagus (Asparagus) and thehearts of the dwarf fan palm (Chamaerops humilis) are savored by thepeople of the northern African deserts; the flower shoots of broomrapes(Cistanche phelypaea [Orobanchaceae] and C. violacaea) are especiallypopular among the Tuaregs, who eat them whole, like asparagus. They arealso eaten in times of scarcity throughout northern Africa. The roots ofsome scorzoneras such as Scorzonera undulata (Asteraceae) are alsohighly edible. Many more plants are used as condiments, especiallyLamiaceae such as capitate thyme (Thymus [=Coridothymus] capitatus),Apiaceae such as Ridolfia segetum, and Asteraceae such as safflower(Carthamus tinctorius).

In the Sahel, two of the best-known species that are appreciatedfor their fruits are 1) the baobab (Adansonia digitata), whose leavesare also eaten (and the water stored in its trunk is sometimes consumed;see vol. 3, p. 76), and 2) the karit or shea butter tree (Vitellaria[=Butyrospermum] paradoxa; see vol. 3, p. 315). Less well-known speciesinclude kutunkuri (Lannea acida, Anacardiaceae) and other members of thesame genus, and the above-mentioned marula (Sclerocarya birrea), whichis eaten fresh or used to make alcoholic drinks. Other fruit-producingspecies of interest include: botsu (Carissa edulis, Apocynaceae); thetamarind (Tamarindus indicus, Leguminosae), of African origin despiteits specific name; Combretum aculeatum (Combre-taceae); Diospyrosmespiliformis (Ebenaceae), one of the western African ebonies; Parkiabiglobosa (Leguminosae-Mimosoideae), known locally as duaga; the jujubeZiziphus spina-christi (Rham-naceae); Feretia apodanthera, Canthium, andGardenia (all three Rubiaceae); Salvadora persica (Salvadoraceae), whoseleaves and twigs are also used in oral hygiene; Celtis integrifolia(Ulmaceae); and Vitex doniana (Verbenaceae). Both the fruit and thetender hearts of some species of palms are eaten, among them Borassusaethiopum and Hyphaene thebaica.

In the North American deserts, the hearts of some palms such as theSonora palmetto (Sabal uresana) are also eaten. The fruit of theCalifornian desert fan palm (Washingtonia filifera) can be consumed aswell, and this palm provided the Coahuilteco Indians and their neighborsin the Sonoran and California deserts with materials for constructionand basket making. The fruits of the mesquite (Prosopis chilensis [=P.juliflora], Leguminosae-Mimosoideae) and the screw bean (P. pubescens)were also eaten by many of these peoples. Mescal, or pulque, is agreatly appreciated alcoholic drink made by fermenting and distillingthe sap of the inflorescence of several species of Agave (see p. 210).The sweet fruit of prickly pears (Opuntia), known as tunas in Mexico,are popular as well, both in their area of origin and in northern Africaand the many areas of the Mediterranean Basin where the prickly pear (O.ficus-indica) has become naturalized.

Curative, poisonous, and aromatic plants

Countless medicinal plants grow in the deserts and subdeserts.About 40% of the known plant species of the subdesert wastes of northernAfrica are used in traditional medicine, and they still represent amajor contribution to the region's economy. In 52% of thesespecies, the organs used are stems and leaves, in 33% fruits, seeds andflowers, and in 15% roots and bulbs. Most are also common in theMediterranean Basin (Ajuga iva, Marrubium vulgare, Peganum harmala,Teucrium polium, Lavandula multifida). The tar obtained from the resinof the arar (Tetraclinis articulata) is used against mange in camels andalso as a varnish. Deverra [=Pituranthos] tortuosa (Apiaceae) preventscontamination within cisterns. The Apiaceae includes species such as thevisnaga (Ammi visnaga), whose fruits act as diuretics and vasodilators;aniseed (Anethum graveolens) and fennel (Foeniculum vulgare), used ascondiments in cookery and for a variety of therapeutic purposes; andgiant fennel (Ferula communis) and turpeth root (Thapsia garganica),whose roots are used as pain relievers, powerful purgatives, andantidotes to poisons, although at high doses they are toxic.

The poptato family (Solanaceae) includes many species withmedicinal properties, especially the henbanes (Hyoscyamus), whichcontains alkaloids that when consumed give a feeling of weightlessness.Apart from its toxic properties, and its uses as a hypnotic and againstall sorts of convulsions, henbane is also used against asthma,toothaches, and in creams that relieve muscle and joint pains. Similarproperties are possessed by thorn apples (Datura stramonium, D. metel)and mandrake (Mandragora autumnalis), to which very many otherproperties have been attributed. Withania (Withania somnifera) is anarcotic. Castor oil, extracted from the seeds of the castor oil plant(Ricinus communis) is used as a purgative, while the highly toxic rootof Atractylis gummifera has traditionally been used by murderers topoison people.

Noteworthy plants of the deserts and subdeserts of southern Africainclude the grapple plant (Harpago-phytum procumbens, Pedaliaceae),which is used to treat kidney stones and arthritis. The tuber of theBauhinia [=Tylosema] esculenta (Leguminosae), the morama bean, is asource of starch. The medicinal plant Vangueria infesta (Rubiaceae), aswell as Lippia jaranica (Verbenaceae) and L. scabra, are taken as herbteas, as is Artemisia afra, which produces a tea that helps digestion(Boer tea).

The different species of the genus Opuntia are abundant in the hotdeserts and subdeserts of Mexico and the southwestern United States, andtheir fruit and stem pads contain pectin, which soothes coughs andlowers cholesterol levels. This has been confirmed in clinical studies,which have shown that these species affect tolerance to glucose,insulin, serum lipids, and beta cholesterol, and lower blood sugarlevels. Though they are not strictly curative, it is also worthmentioning the aromatic frankincense trees Boswellia frereana and B.carteri (Burseraceae). They grow in the subdeserts of the Horn of Africain the fog zone from 2,297-5,577 ft (700-1,700 m) on the escarpment inSomalia that dominates the coastal plains of the Red Sea.

Dye and tannin producing plants

The biochemical properties of a large number of desert plants makeit possible to obtain a wide range of different natural products--frompigments to mordants for tan skins and hides. Mention has been made ofthe use of the leaves of jicid as a dye, though it is only importantlocally. Henna and anchusine are much more important dyes.

Henna is obtained from Lawsonia inermis (Ly-thraceae), originallyfrom northern Africa and southwest Asia but now widely cultivatedthroughout the tropics and even the Mediterranean Basin. The finelyground dried leaves are mixed with water to prepare a paste to dye theskin, hair, eyebrows, and nails a reddish color; when mixed with indigo(extracted from species of Indigofera) before application, henna makesthe hair a shiny black. As it is fast-acting, it was formerly used todye textiles and skins. The mummies of the ancient Egyptians werewrapped in cloth dyed with henna. In traditional medicine in Islamiccountries, henna has been used to reduce fever and as an astringent. Theleaves were placed in the armpits as deodorants; mixed with Acacialeaves to cure cuts on the hands and feet; and mixed with vinegar to getrid of headaches. It is also thought to have abortion-inducingproperties.

Anchusine, a scarlet coloring agent, is obtained from the roots ofthe herbaceous perennial dyer's alkanet (Alkanna lehmannii [=A.tinctoria], Boraginaceae). Anchusine is used to color oils, cosmetics,medicines, thermometer fluids, and low-quality wines. It is also used inmicroscopy to detect oils and fats in tissue sections. It has, however,been replaced for most of these uses by synthetic coloring agents suchas Sudan IV (a diazocompound that is bright red).

Major sources of tannins are found in plants that grow in thewastelands and thyme scrubs of North Africa. Among these plant parts arethe roots of sumacs (Rhus pentaphyllum, R. tripartitum) and mastics(Pistacia lentiscus, P. atlantica) and the leaves and stems of thestorksbill Erodium glaucophyllum (Geraniaceae), whose tubers are agreatly appreciated foodstuff.

Fibers and wickerwork

Basketwork has been important in many desert and subdesertcultures, as a nomadic lifestyle discourages carrying too manybelongings, especially those that are heavy or fragile. In thesecultures, woven baskets are not easily displaced or replaced by ceramicones. Even after becoming sedentary, the shortage of fuel discouragesmaking things that consume too much fuel. Many peoples of the hotdeserts and subdeserts, not just the famous Anasazi (or Basket MakerIndians), have made excellent baskets with the materials provided by thedesert flora.

The subdesert steppes of northern Africa, for example, aredominated by species of perennial grass, among them two esparto grasses(Stipa tenacissima and Lygeum spartum) that have played an importantrole in craft production of basket and mats in the region, and also insome areas of the Mediterranean Basin, where this tradition stillsurvives, though not as vigorously as in the past. Stipa tenacissimagrows wild in the most arid areas of the Iberian Peninsula. A robustclump-forming perennial with shallow roots, it has been introduced tomany areas of the world. Its fiber has traditionally been used in localcrafts as ropes for boats (esparto rope is highly durable but so lightit floats on water), more everyday types of rope, harnesses for draftanimals and beasts of burden, mats, curtains, and other objects, but itwas also exported (after collection and baling) for the manufacture ofhigh quality paper, especially cigarette papers.

The exploitation of esparto grass was abandoned many years ago inLibya and Morocco and is dying out in Algeria and Tunisia. This isbecause productivity has declined greatly and mechanization cannot beintroduced. But the decline in area and yield are not only caused byoverexploitation.

In the countries where esparto has not been traded for years, thereis continuous degradation as a result of overgrazing, fires set byherders, trampling, erosion, and especially plowing to cultivatecereals, even though the harvest is highly uncertain. Once destroyed,esparto cannot regenerate, as in these desert areas it can only dispersevegetatively by its outward-spreading rhizomes. (Sexual reproductionrequires the slight shade of open grasslands.) Steppes of the otheresparto grass, albardine (Lygeum spartum), sometimes occupy a dynamicstage intermediate between esparto scrub and shrubland.

Unlike S. tenacissima, it can regenerate from seed in its actualhabitat. Its fiber has traditionally been used in local crafts for thesame purposes as esparto, but the way it is used and valued has onlybeen studied from the point of view of ethnography and art. Craftproduction using esparto is rapidly declining because of the appearanceof plastic fibers.

Other species of grass such as the giant reedor Spanish cane(Arundo donax) and common reeds (Phragmites spp.) are also used inbasketmaking, as are the fronds of the date palm (Phoenix dactylifera),the dwarf fan palm (Chamaerops humilis), and, in the North Americandeserts, the desert fan palm (Washingtonia filifera). Basketmakers inthe North American deserts obtained most of their materials from waterholes or dry river beds where the water table was near the surface andwhere there were abundant trees producing suitable shoots (Salix,Chilopsis linearis), cattails (Typha), and several species of sedge andgrass. They were plaited into a spiral and woven on a wicker frame thendyed a range of colors with coloring agents also obtained from plants.

Timber and firewood

Trees are scarce in deserts, but where they are present they growslowly and produce hard long-lasting wood. Overlogging has considerablyreduced their populations and has modified the distribution of ageclasses, and thus size, of the desert trees. The largest trees (theoldest) have now disappeared. In the northern tropical arid regions ofthe Old World, it is possible to find the giant tamarisk (Tamarixaphylla, Tamaricaceae) whose wood has been used in carpentry since thetimes of the ancient Egyptians. (The largest trunks were made intosarcophagus lids.) Overexploitation means it is no longer possible tofind such large trunks; the giant tamarisk trees, or at least thespecimens now growing, no longer live up to their name.

Conocarpus lancifolius (Combretaceae) is another tree from thisregion whose trunks are no longer large enough for their traditionaluse, the construction of boats (dhows). This tree grows on the alluvialterraces of wadis and areas where springs emerge or where there is ashallow water table near the coast. It is now used to build houses andfences, in carpentry, turnery, and in carvings, as well as for goodfirewood and excellent charcoal.

A versatile tree, it also provides food for goats and otherlivestock (in times of drought, the branches are cut to obtain fodderfor livestock) and wild herbivores, and an alcoholic drink is made fromits fragrant flowers. In cities like Mogadishu and Khartoum, it isplanted along the avenues and is also used in windbreaks to stabilizethe soil and to reforest former limestone quarries. The ground-up leavesare used as a fishing poison and the gum resin is traditionally used totreat people and animals for stomachache and lung disorders.

Surprisingly, some cacti also provide valuable timber. The centralwoody skeleton of several columniform cacti (known as cardones inArgentina and Chile), including the Atacama pasacana (Tri-chocereusatacamensis) and the pasacana proper (T. pasacana) of the puna andmonte, is widely used to make beams, doors, and furniture. The woodyskeleton of the saguaro (Carnegiea gigantea) from the Sonoran Desert isused for the same purposes, as are other cacti of the North Americandeserts such as the Mexicangiant or cardo pelon (Pachycereus pringlei)of the Sonoran and Vizcaino deserts. The ocotillo (Fouquieria [=Idria]columnaris) is frequently used to build wooden huts, which are thenroofed with clay and straw. In Africa, the cactuslike spurges (Euphorbiaabyssinica, E. candelabrum, E. tirucalli,) have traditionally been usedto construct palisades and fences. The bushman's candle(Sarcocaulon malothii, Geraniaceae) is used in a remarkable way by theSan of southern Africa. This pachycaul shrub's bark contains ahydrocarbon-rich wax, which they burn as a torch.

Ornamental plants

Many trees from the Sahel subdeserts are greatly appreciated asstreet trees because they are attractive and require very little water.Examples include members of 1) the Meliaceae, including the or neem tree(Azadirachta indica), also valued for its natural pesticides with few ofthe undesirable side effects of synthetic insecticides; 2) theTamaricaceae, including the phraetophyte Tamarix stricta from Pakistanand Tamarindus indica from Africa; 3) the Combretaceae, including hodeti(Conocarpus lancifolius) from Somalia; and 4) the Leguminosae, includingshishamor sissoo (Dalbergia sissoo), the kassod tree (Cassia siamea)from India, the Jerusalem thorn (Parkinsonia aculeata) of the Americandeserts, the mesquite (Prosopis chilensis [=P. juliflora]), the jhand(P. cineraria [=P. spicigera]), the babul (Acacia nilotica subsp.indica) from India, and kad (A. [= Faidherbia] albida).

The deserts of southern Africa are home to a large number ofornamental plants, mainly from the families Proteaceae, Geraniaceae, andespecially succulents and nonsucculents from the families Aizoaceae andAsteraceae. The contribution of the American deserts includes theirgreat diversity of cacti (Cactaceae) and agaves (Agavaceae).

2.2 Grazing in arid areas

The secondary production of the pastures of the arid and semiaridtropical regions is very low, as the grasses are of little nutritionalvalue--except for the few weeks before flowering--and therefore cannotsupport the livestock. These poor pastures of grass that can be grazedor scrub and shrubs that can be browsed by livestock are, however, themost important grazing resource in the hot deserts.

The deserts and subdeserts of North Africa

As far as plant resources--and especially grazing resources--areconcerned, probably the world's best-studied areas of hot desertare those of North Africa. Extensive grazing areas and fallow groundoccupy most of the subdesert scrub in the region. Of a total of 630,000[km.sup.2], pastures occupy 70%, about 440,000 [km.sup.2]. Pastures alsooccur in the depressions and the vegetated areas of the Sahara, about 5%of the desert's area (430,000 [km.sup.2]; of a total of 8.6 million[km.sup.2]).

These formations are the basic food supply for almost 50 millionsheep equivalents, roughly one sheep per hectare (1 ha=2.5 acres), andthe many types vary greatly depending on the site's climate, soil,and management. Each type has its well-established floristiccomposition, with its dominant species, some of them especially soughtout by the livestock and thus considered to be preferentially grazed.The bulk of the food supply for these animals is now based on grains,straw, cane, and a wide range of agricultural residues (leaves and twigsof fruit trees, olive stones, rejected dates, bran, and other residuesfrom milling and flour mills), as well as the produce from somesylvo-pastoral plantations. Even so, approximately one-third of thetotal plant species of these scrublands regularly form part of thelivestock's food supply.

The average annual epigeal production of the thyme scrubs ofnorthern Africa is about 3 kg dry matter/ha per year and per mmrainfall, though in practice this varies from 1-6 kg, depending on theconditions, and is about 100-300 kg dry matter/ha on the edge of theSahara and 400-1,200 kg dry matter/ha per year on the edge of thesemiarid zone. The aboveground perennial plant biomass is closely linkedto the extent of cover by the perennial layer. Each 1% of plant covercorresponds to a plant biomass of 30-60 kg. The aboveground plantbiomass of the annual species corresponds, by definition, to theirannual production, and this is highly variable. In the less degradedthyme scrubs, it represents an average of 25% of total primaryproduction. The annual species' share of the total plant biomass,however, increases as the scrub is degraded and may reach almost 100% inthe areas that have been turned into deserts. This relationship betweenthe epigeal plant biomass and the extent of perennial plant cover doesnot apply to other types of subdesert formations.

The Sahel

The ecological region known as the Sahel lies south of the Sahara,between the 4 in (100 mm) and the 24 in (600 mm) annual rainfallisohyet. It occupies a strip 373 mi (600 km) wide (from north to south)and 3,107 mi (5,000 km) long (from west to east) and thus occupiesroughly 3 million [km.sup.2]. It is a stockraising area with subsistencecrops such as pearl millet (Pennisetum glaucum), sorghum (Sorghumbicolor), and cowpea (Vigna unguiculata), some industrial crops such aspeanuts (Arachis hypogaea) and cotton (Gossypium hirsutum), and a fewirrigated crops, including sugarcane (Saccharum officinarum), on thesouthern edge.

Despite the dominance of the herbaceous layer, the woody speciesare very important in the Sahel pastures, as they are the main source ofprotein for the herbivores during the nine-month-long dry season. Inthis period, the herbaceous layer consists of nothing more than drystraw left over from the previous wet season; it is relatively rich inenergy but contains almost no phosphorus, protein, or carotene(precursor of vitamin A). In theory, these woody plants could bereplaced by concentrated feeds, seeds (cottonseed), or urea. But thisreplacement is not economically viable, taking into account the currentterms of exchange, especially the huge cost of transport and the lowprice of meat. The woody plants are such essential sources of proteins,phosphorus, and carotene during the dry season that their disappearancewould inevitably lead to the end of grazing in the area outside theshort rainy season (one-to-three months long).

In the northern Sahara or Saharo-Sahelian zone, the area betweenthe 4 in (100 mm) and 8 in (200 mm) annual rainfall isohyets, there arepastures dominated by perennial grasses (Panicum turgidum, Aristidapallida, A. papposa, Lasiurus scindicus, Cymbopogon schoenanthus) andsome sedges (Cyperus conglomeratus [=C. jeminicus]). The average primaryproduction of these pastures is 100-200 kg dry matter/ha per year, thatis to say a rainfall efficiency use coefficient of 1-4 kg dry matter/haper year and per mm rainfall, and a carrying capacity of 1 TLU (tropicallivestock unit) per 45-275 ha. One TLU corresponds to the unitequivalent to a bovid with a live weight of about 550 lb (250 kg) thatneither gains not loses weight, consuming 6.25 kg dry matter per day(2.5% of its live weight or 10% of its metabolic weight [metabolicweight equals: of its live weight]). This represents annual consumptionof 2,280 kg dry matter (an estimated 25-30% of plant cover is consumed).The different livestock species reared in the Sahara can be given thefollowing values in TLUs: cattle 0.81; sheep 0.18; goats 0.16; asses0.53; and camels 1.16 (values based on the ratio of the mean metabolicweight and body weight for the population of each species).

The Sahel zone is characterized by a vegetation consisting ofslightly or very spiny woody plants (Acacia ehrenbergiana, A. laeta, A.nilotica, A. senegal, A. tortilis, Guiera senegalensis, Maeruacrassifolia, Balanites aegyptiaca, Commiphora africana, Bosciasenegalensis, Cordia sinensis, Ziziphus mauritania, Grewia bicolor, andEuphorbia balsamifera). These are more or less regularly scattered abovea herbaceous layer dominated by annual grasses (Aristida funiculata, A.mutabilis, A. adscensionis, Cenchrus biflorus, Eragrostis tremula,Pennisetum mollissimum, Dactyloctenium aegyptium, Schoenefeldiagracilis, Panicum laetum, and Tragus racemosus). The number of stems ofwoody plants per hectare varies from 0-500, though normally there are20-80 stems/ha, with a canopy cover of 5-20%. The leaves, shoots, andeven the branches may be an important addition to the livestock'sdiet when the highly variably production of the grass layer does notprovide enough for the livestock to feed upon. The aboveground primaryproduction of the herbaceous layer may be 1,000-2,000 kg dry matter/haper year (or as high as 3,000 kg/ha per year in silty depressions withplenty of water). Average annual aboveground production is about 1,200kg dry matter/ha. The average number of days of grazing per year isabout 50, representing a load of 1 TLU per 7.3 ha. The apparentconsumption would be 25-30 kg per day, though the real figure is 6.25.

The Sudano-Sahelian region receives an average annual rainfall of16-24 in (400-600 mm). The Saharo-Sahelian zone and the Sahel sensustricto are totally covered by sand, the result of the southward spreadof the Quaternary Saharan ergs, especially the Ogolien erg(10,000-20,000 years ago). The soils of the Sudan-Sahelian zone are,however, very diverse, as is land use. The deepest and most favorablesoils and the floodable depressions are used for agriculture. On sandysoils, millet and groundnuts can be cultivated; sorghum can grow onloamy and clay soil; on the southern edge of the zone, cotton may growon the soils with plenty of water. The pastures of the Sudan-Sahel aredistinguished from the true Saharan ones by the presence of theperennial grasses (Andropogon gayanaus, Hyperthelia dissoluta) and ofseveral woody species (Acacia [=Faidherbia] albida, A. seyal, A.ataxacantha, A. mellifera, Bauhinia rufescens, Pterocarpus lucens,Terminalia avicennoides). The average aboveground primary productivityof this type of pasture is 800-5,000 kg dry matter/ha per year, and theaverage number of days of grazing per year is about 40, equivalent to agrazing load of 1 TLU per nine hectares. In silty and clay depressions,primary productivity is about 3,000 kg/dry matter per ha per year withabout 160 days of grazing per year, equivalent to 1 TLU per 2.3 ha, butin the floodable grasslands of Echinochloa stagnina this figure isdoubled. The zone's average is about 1,800 kg dry matter/ha peryear with about 90 days of grazing, equivalent to a grazing load of 1TLU per 4 ha.

The deserts and subdeserts of southern Africa

The deserts and subdeserts of southern Africa occupy about 2million [km.sup.2] in South Africa, Botswana, Namibia, and a small partof Angola. About 310,000 [km.sup.2], the Atlantic coastlines of Angola,Namibia, and South Africa, can be considered authentic desert, the NamibDesert. The arid zones include much of Botswana and Namibia, 50% ofSouth Africa, and a small area of southwest Angola. About 80% of thisarea is at an elevation of 3,281-4,921 ft (1,000-1,500 m). Theregion's flora (9,000 species) shows remarkable diversification, asdoes the vegetation, which includes scrub and shrubland (comparable tothose of the Mediterranean Basin) on the other side of the Africanlandmass and arid savannahs comparable to those of the Sahel. The scruband shrubland of the Karoo occupy almost 550,000 [km.sup.2] in SouthAfrica (most of it) and Namibia. There are about 20 types of scrub thatcan be classified into three major groups: grassy, chamaephytic, andsucculent. The first two form what is known as Nama Karoo.

Grassy scrub is especially common in the northern Karoo, betweenthe Orange River, the Namib, and the Kalahari. Average annual rainfallis 5-12 in (120-300 mm). The soils are sandy and covered with a veryhard, dense, calcareous crust. They are dominated by perennial grasses(Stipagrostis uniplumis, S. namaquensis, S. amabilis, Themeda triandra,Heteropogon contortus, Eragrostis curvula, E. lehmanniana, Aristidadifusa, A. congesta, Schmi-dtia pappophoroides). When the calcareouscrust is at the surface, the shrub Rhigozum trichotomum (Bignoniaceae)tends to become dominant. There are also some trees such as theshepherd's tree or witgat (Boscia albitrunca), the camel thorn(Acacia erioloba), the umbrella thorn (A. tortilis subsp. heteracantha),and other species of the same genus (A. mellifera subsp. detinens, A.hematocarpa, A. hebeclada). The limited potential of the pasture meansthat their carrying capacity is about one sheep per 4-6 ha (1 ha=2.5acres).

Chamaephytic scrub occupies most of the Karoo, where average annualrainfall is 8-16 in (200-400 mm). This type is similar to theMediterranean and subdesert thyme scrub of northern Africa inphysiognomy, but the floristic composition is totally different. Thesoils are usually sandy-silty or silty and shallow, overlying a veryhard, thick, calcareous crust of Pleistocene origin. Every 3-4 ha ofthis scrub can support on average one 45 kg ovineunit (the averageconsumption of plant biomass is 200 kg dry matter/ha per year, and thetotal plant biomass is 800-1,000 kg dry matter/ha per year). Theprecipitation-efficiency index is 3-4 kg dry matter/ha per mm rainfall.The dominant species are chamaephytes belonging to the family Asteraceaesuch as ankerkaroo (Pentzia incana) and other species of the same genus,pteronias (Pteronia), etc. There are also some succulent chamaephytesbelonging to the Aizoaceae and Crassulaceae, as well as severalperennial Poaceae.

A coastal strip extends the Namib to the south from the latitude ofLuderitz (Namibia) to Lambert Bay (Cape Province), then expands inlandof the province between the Mediterranean fynbos and the Karoo proper(or Nama Karoo); this is known as the succulent Karoo and consists ofdry subdesert to desert pastures. Average annual rainfall is 3-10 in(80-250 mm). The dominant species are chamaephytes belonging to thefamilies Aizoaceae (Galenia, Drosanthemum), Crassulaceae (Cotyledonorbiculata and species of Crassula, Andromischus, and Cotylecodon), withthe occasional presence of chamaephytes of the family Asteraceae. Thereare also some annual or short-lived perennial grasses. The soils ofthese succulent scrublands are generally superficial and often saltyand/or sodic, which explains the frequent presence of members of theZygophyllaceae (Zygophyllum, Augea) and Chenopodiaceae (Salsola,Atriplex). The carrying capacity of these scrubs is very low, roughlyone sheep per 10 hectares.

2.3 Sylvo-pastoral plantations

A significant part of the plant resources exploited by the herdersof desert and subdesert Africa are not derived from the naturalvegetation but from new pastures deliberately created by reinforcing thewoody species. They are known as sylvo-pastoral plantations and coveralmost a million hectares in the arid zones of northern Africa alone.Promoted and subsidized by state governments, they aim to provide fodderto complement the pastures during the episodes of shortage followingdroughts and are also an effective way of rehabilitating degraded areas.

African repopulated pastures

The strategy against the effects of drought adopted by the farmersand herders of the Karoo subdeserts is to plant drought-resistant foddershrubs: cacti such as prickly pears (Opuntia ficus-indica) and otherspecies of the same genus (O. robusta, O. fusicaulis), agaves (Agaveamericana), and saltbush (Atriplex nummularia). The total planted areais about 800,000 ha (1 ha=2.5 acres), about 500,000 of them planted withcacti, 200,000 with saltbush, and 100,000 with agaves. The productivityof these plantations is about three to five times greater than that ofan area planted with nonresistant species. Production of the cacti canbe left to accumulate for two to three years, the saltbush for six tonine months, and the agaves for 5-7 years. This allows the farmer andthe herder to store substantial fodder reserves for when the droughtarrives.

A similar strategy is practiced in the subdesert pastures ofnorthern Africa, especially in Tunisia. The main species used in theupper layer are acacias, originally from the arid regions of Australia,mainly Acacia saligna, A. salicina, and A. cyclops, while the mainspecies in the lower layer are saltbushes of different origins (Atriplexnummularia from Australia, A. halimus from the local flora) and pricklypears (Opuntia ficus-indica). Each hectare of these plantations providesas much fodder as 3-5 ha of undegraded natural pastures, with apluviometric efficiency-index of 8-10 kg dry matter/ha per year per mmrainfall within the 4-16 in (100-400 mm) rainfall interval. The Acaciaand Atriplex also provide firewood that is greatly appreciated by thelocal people.

The Australian mulga

Mulga (Acacia aneura) is a small Australian tree up to 46 ft (14 m)tall that grows in areas with annual rainfall of 8-15 in (200-380 mm).The last 4-12 in (10-30 cm) of the branches bear phyllodes (modifiedpetioles) that are narrow and flattened or cylindrical. The root systemis extensive, consisting of long radial roots that anchor it to thesubstrate and other much more branched roots that penetrate at an anglein search of water. This root system is so effective that there islittle or no ground cover, and mulga normally forms single-speciesforests or very open scattered patches. The summer and winter rains,despite their scarcity, are vital to the survival of the mulga, whichcan grow and flower at any time of year when there is rain.

The mulga is a highly variable species that adopts four differentgrowth forms in Australia. Low mulga, consisting of small shrubs orsubshrubs, is the result of constant browsing by sheep and cattle and isa very important source of fodder during droughts. Whipstick mulgaconsists of immature trees with thin straight branches that only bearleaves at the tips; these leaves are not available to the livestockwithout the use of heavy machinery. Umbrella mulga consists of matureshrubs with thin upright branches covered with leaves that respond verywell to pruning; although its nutritional value is not very high, itforms the main standing reserve for browsing by sheep during longperiods of drought. Mulgacopses with 175-200 trees/ha, when pruned,provide the best combination of grazing and browsing during the dryseason. Leaf palatability varies greatly, but 1.4 kg of leaves per dayis enough to feed a sheep, as long as its diet is complemented withsulfur and phosphorus. Finally, high mulga consists of forests of oldtrees with bare trunks that only bear leaves on the highest stems. Theseleaves are usually palatable but inaccessible to the livestock.Furthermore, these trees do not tolerate pruning, so that they cannot becut for fodder without killing them. The trees of the high mulga usuallyproduce large quantities of seed.

2.4 Agricultural activity

Agricultural activity is impossible in true deserts and occurs onlyin oases or on riverbanks, where irrigation is possible. In thesubdeserts, some unproductive dry farming is possible, but it isunreliable and the fallow periods have to be long.

Dry farming

In general, dry farming is possible if average annual rainfall isgreater than 16 in (400 mm). If rainfall is a little greater, it is alsofeasible in areas where the climate is bimodal; in regions with averageannual rainfall of only 8 in (200 mm), in some years it is possible toget crops to grow. In any arid or semiarid region, however, soilstabilization and the application of water conservation techniques areessential if agriculture is to be sustainable. In any case, herbaceouscrops have little chance of growing well in these regions, due to theirsuperficial roots.

Dry farming of trees produces better results in the subdesertregions of northern Africa. Unirrigated fruit trees occupy about1,600,000 ha, most (1,400,000 ha) in Tunisia, about 150,000 ha inwestern Libya (Tripolitania), and about 50,000 ha on the northwesterncoastline of Egypt to the west of Alexandria. In Tunisia and Libya, 80%of these crops are olive trees, while in Egypt, figs account for 80% ofthe area cultivated. In both cases, the remaining 20% of dry farmingtree crops consists of secondary species such as almonds, pomegranates,apricots, peaches, table grapes, date palms, and, of course, figs inTunisia and Libya and olives in Egypt. Unirrigated tree crops areusually grown on deep, relatively coarse, sandy soil, and soproductivity is generally satisfactory, 600-1,200 kg olives/ha per year.When the soil is finer-textured (fine sands and silt), hydraulictechniques have to be used to control and make use of the runoff. Amongthese water-saving strategies are the use of the tabia (a sort of ridgebetween two furrows that runs perpendicular to the direction of therunoff, thereby slowing it down and increasing the infiltration of waterinto the soil) and jessur (building dry walls along the course of a wadifor the same purpose).

When the soil is sandy, the distance between the trees is verylarge, 66-82 ft (20-25 m) for olives and 33-39 ft (10-12 m) for almondsand other members of the rose family (Rosaceae). This means a singlehectare can only support 16-25 olive trees and 70-100 trees of otherspecies. In crops that use runoff, the density is variable, but onaverage they may be twice the densities given above and four times inthe case of vines (up to 400-600 stems/ha). In central Tunisia, whereannual rainfall is 8-12 in (200-300 mm), average annual production isabout 35 kg per tree, about 700 kg of olives/ha or 160 kg of oliveoil/ha per year. Such a high production, despite the low rainfall andsandy soil, is easily explained. Of the 8 in (200 mm) of rainfall peryear, 4 in (100 mm) is lost through evaporation, while the other 4 in(100 mm) infiltrates into the soil, protected from evaporation butavailable to the trees. The cover of the canopies of the olives, about1,000 m2/ha, or 10%, loses the infiltrated water by evapotranspiration.If the cover were 100%, the evapotranspiration would be 39 in (1,000mm), a value corresponding to the water consumption of an irrigated cropor a crop in the Mediterranean zone with a wet climate.

Irrigation-based agriculture

In the regions where rainfall is too scarce for dry farming,certain types of agricultural production are possible if the water tableis quite high and irrigation is possible. The high rates of evaporation,however, may cause problems of soil salinization; agricultural land hasbeen lost all over the world through excessive soil salinity, which ismore or less related to irrigation of crops. Irrigation considerablyincreases crop production and guarantees a harvest in years of little orno rainfall. The Papago of the Sonoran Desert managed to cultivate thetepary bean (Phaseolus acutifolius, Leguminosae), a species of desertorigin, with the water from a single summer shower channeled to theirvegetable plots using a system of ridges and strengthened dams. Typicaldesert irrigation is practiced in oases, growing vegetables and greens,fruit crops (citrus fruits, bananas, apricots, olives, avocado pears,guavas, palms, and pomegranates), and even industrial plants such ascotton, beetroot, fodder plants, and cereals. In northern Africa, thevalue of these harvests is about $2 billion a year, representing 31% ofthe entire local agricultural sector. On river banks, especially on thelarger rivers such as the Nile, Tigris, Euphrates, and Colorado, moreland is suitable for agriculture and communications are better, so thatmost of these fruits and vegetables can be cultivated commercially.

Palms

The date palm (Phoenix dactylifera), probably originally fromArabia, has been cultivated for 5,000 years in all the Saharan oases inArabia, in the Nile Valley (in northern Sudan and Egypt), and along therivers Tigris and Euphrates. It has recently been successfullyintroduced as a commercial crop into California, Arizona, andQueensland. As date palms are dioecious (male and female flowers areborne on different plants), production is greatest when the number ofmale plants is kept as low as possible. Natural wind pollination isenhanced by placing pieces of the male inflorescence in close contactwith the female one. Ritual fertilization of date palms is known to havebeen practiced by the civilizations of ancient Mesopotamia.

The date palm has more than 800 different uses, making it a truemultipurpose species. The fruit can be eaten fresh or dried and can bemade into a syrup and an alcoholic drink called arrack. The palm'sheart can also be eaten, as can the flowers and pollen, and the rootscan be fed to livestock when the stem is cut. The stem is widely used incoverings for buildings, pillars, roofing, small bridges, and irrigationchannels, while the date stones are made into a high quality charcoalused by silversmiths. The fibers are used to make rope, and a wide rangeof baskets and the leaves are woven into bags and baskets (see vol. 5,pp. 278-279).

The African palmyra palm (Borassus aethiopium), with itscharacteristic swollen stem topped by a tuft of fan-shaped leaves, iswidespread throughout the more arid regions of tropical Africa, whileits relative the palmyra palm (B. flabellifer) occurs throughout thedrier tropical zones of Asia as far as eastern Malaysia. Both specieshave multiple uses, though the African species is not used as much asthe Asian one. Their fruits are edible but are not commerciallyexploited. The petioles of B. flabellifer are also a source of fibers.

Safflower and other industrial crops

Cotton is the most important industrial crop in the oases of theAfrican deserts, but other major crops include cereals (wheat, sorghum,and millet), legumes such as kidney beans (Phaseolus vulgaris), thepigon pea or arhan (Cajanus cajan), the cow pea (Vigna unguiculata [=V.sinensis]), and oil crops such as the sunflower (Helianthus annuus),peanut (Arachis hypogaea), sesame (Sesamum indicum), and especiallysafflower.

Safflower (Carthamus tinctorius, Asteraceae) is not known in thewild but seems to have originated in Arabia. It was cultivated inancient Egypt, and since then it has spread throughout the Mediterraneanand east to China. More recently, the Spanish introduced it into Mexico.In Egypt, the Middle East, and India, the dried flowers were used toobtain carthamin, a red textile dye and food coloring agent. Saffloweris sometimes still used as a substitute for saffron or to adulterate it.Now mainly grown for the oil extracted from the seeds, safflower hasbeen cultivated on a large scale in the United States since the 1950s,and production may exceed 4,500 kg/ha. The world's largestproducers are India (about 450,000 tons), where the oil pressed fromsafflower seeds is used in cooking, in lighting, and to make soap,followed by Mexico (25,0000 tons) and the United States (100,000 tons).Safflower oil is very healthy and tastes good, but outside India it ismainly used in paints and therefore is not an important human foodstuff.

The hopes raised by jojoba plantations

The jojoba (Simmondsia chinensis) is the only member of its family,the Simmondsiaceae. It is a dioecious, semideciduous, plant with ashrubby growth-form that can grow to a height of 10 ft (3 m), andproduces a fruit resembling an acorn, containing a single seed oroccasionally two. The fruits ripen in early autumn and shed their oilybrown seeds onto the ground, where they are greatly appreciated by sheepand goats, as well as humans, especially children, who gather them atthe base of the tree. The Mexicans make a nutritious and tasty drinkwith the seeds of the jojoba: they are toasted and ground with the yolkof hard-boiled eggs, then the paste is boiled with water, and milk andsugar are added.

The jojoba (Simmondsia chinensis) is originally from the hot NorthAmerican deserts. Its specific name, a misinterpretation by the botanistwho described it, resulted from a mix-up between collections fromCalifornia and China. It was first mentioned in the diaries of theJesuit priest Eusebio Kino, who in a letter to Philip V of Spainreferred, together with the other resources used by the Pima Indians, tothe medicinal jojoba fruit. Later, in 1789, Francisco Clavijero statedin his Storia della California that this fruit was valuable for itsmedicinal properties and was widely used to ease childbirth, to healwounds, and to cure difficulty in urination due to mucus concretions.The oil extracted from the seeds was also considered an excellent remedyagainst cancer; it is so tasty that some people in California use it insalads instead of olive oil.

Jojoba oil was analyzed for the first time in 1895 by Leon Diguetof France who recommended jojoba cultivation to the French colonists innorthern Africa for its edible fruit. The interesting molecularstructure of jojoba oil was not discovered until 1933. Jojoba oil, inreality a liquid wax, is a fatty acid molecule joined to a long-chainalcohol. No other plant is known to produce an acid-alcohol ester ofthis type in its fruits. The fruit contains 40-60% oil, which is ofgreat economic importance as a lubricant for delicate instruments and inindustrial processes involving high temperatures and pressures. It mightalso be a good chemical intermediary for products used as wetting agentsand high-pressure additives. It is now cultivated commercially inseveral desert regions, but production is mainly for the cosmeticsindustry, as it does not turn rancid like other oils and its similarityto sperm oil (see vol. 10, p. 263) has given rise to hopes thatincreasing jojoba production will help to conserve the sperm whale. Intraditional cosmetics, it has been used to stimulate cell and hairgrowth. The rapid increase in production, especially in the UnitedStates, has brought the price of jojoba oil down to about half a dollara kilo, well below the $60 a kilo it cost in 1975 or $30 dollars in1985. Even so, it is a profitable crop with great potential forexpansion to meet the huge market.

3. The use of animal resources

3.1 The exploitation of the native fauna

Potentially a major resource, the fauna of large mammals and birdswas decimated in the first half of the twentieth century and now is onlyof secondary economic importance in the subdeserts of northern Africa,the Sahara, Sahel, and the deserts and subdeserts of southwestern Asia.Some species from hot deserts have been domesticated extremelysuccessfully. Two of the most important domesticated animals--the ass(Equus asinus) and the dromedary (Camelus dromedarius)--are originallyfrom deserts. The wild fauna includes major fisheries in some largerivers of external origin that cross deserts.

Fishing in the middle of the desert

It may seem absurd to include a section on fishing in deserts, butthe large rivers that cross hot deserts provide abundant and variedfishery resources. One particularly well-studied case is the inlanddelta of the River Niger, on the edge between the Saharan and Sahelianregions in Mali. The Niger's source is on the northern slopes ofthe Guinea Highlands. It then flows broadly northeast to Tombouctou,where it turns east to the Tosaye, then turns southeast and continues inthis direction until it joins the Benoue. From there it flows southtoward its delta, which flows into the Gulf of Guinea.

One of the most interesting features of the course of the Niger isthe presence in its middle stretches of a large flood plain more than311 mi (500 km) long and nearly 62 mi (100 km) wide. It is known as aninland delta because, as in a delta, the river splits into countlessbranches as soon as the volume of flow increases slightly, as thegradient in the area barely exceeds 2 cm/km (there is only a drop of 39ft [12 m] between Ke-Macina and Dire, which are 342 mi [550 km] apart).This region is located precisely where the river enters the most aridpart of its basin, with low average annual rainfall (for example, inTombouk-tou, less than 8 in [200 mm], and even at Mopti, right in theheart of the lake region, barely more than 16 in [400 mm]). As theaverage annual rainfall is much greater upstream (more than 79 in [2,000mm] in the upper headwaters of the basin), and this is largely seasonal,the rivers receive major surges at the end of the summer which cause along period of high water, when fishing activity is intense. For therest of the year, fishing is limited to the permanent stretches of theNiger, its tributaries, and the permanent lakes.

The size of the fish catch in this delta area varies greatly(45,000-100,000 tons per year) from one year to the next, depending onthe size of the summer surge, or the total rainfall in the basin.Roughly 200,000-300,000 people live by fishing in the area, and itrepresents 3% of Mali's gross national product (GNP). This fishingis entirely a craft activity using a wide range of methods such asharpoons and three-pronged spears to catch relatively large fish,especially in pools that are drying out or on the flood plains, as wellas large sand barriers called dien that close off entire branches of theriver.

The fish caught vary greatly, but many species of fish are caughtin small numbers. About 85% of the catch consists of just 17 species,the ones that are regularly present in the markets, either fresh, dried,or smoked. The most appreciated fresh fish is Auchenoglanis occidentalis(together with A. biscutatus), a bottom-feeding species of muddy riverbottoms found mainly in flooded areas rather than stretches of theriver. It only represented 2.7% of the catches in 1990-1991 butaccounted for 7.7% of market sales during the period 1982-1991. Thispresence in the markets is exceeded only by a few other species: 1) thetilapias (the commercial name for several species of cichlid fish),which for the same periods represented 26.6% of the catch and 22.5% ofthe sales; 2) the Nile perch (Lates niloticus), known locally ascapitaine, which represented 3.8% of the catches and 8.7% of the sales;and 3) synodontids or lizard fish (a name for 15 species of catfishbelonging to three genera in the family Mochokidae), which used to becaught in abundance but now have declined to less than 1% of catches,though they represented 9% of fresh sales during the period considered.

The drought suffered by the Sahel and the southern Sahara since1973 and reservoir construction on some of the Niger's tributarieshas led to 1) a decline in the area flooded every year on theNiger's inland delta and 2) the appearance of irregular surgesduring the summer low water due to discharges of water from reservoirsto compensate the insufficient volume of flow. This has led to anoverall decline in catches but also a qualitative variation in the fishcaught, with an increase in the catch of opportunistic species such astilapias, and clariids or air-breathing catfish, and a decline in thecatches of other more valuable fish such as synodontid catfish.

The seasonality of production explains the tradition of conservingpart of the catch either dried, smoked, or grilled. The tinameni(Alestes leuciscus) is the source of an oil, which is extracted byboiling. Some species such as the air-breathing catfish (familyClariidae, catfish with gill chambers that allow them to breatheatmospheric oxygen for a while when they are in oxygen-poor water),especially Claris anguillaris and to a lesser extent C. grandisquamis,are almost only eaten smoked. The production of dried and smoked fish isa craft industry carried out in family installations. The installationsfor smoking the fish consist of one or more ovens where the fish areplaced (after cleaning and removing the scales) on a sort of mesh grillover firewood and dry dung (dung smoke appears to improve the color ofthe fish being smoked). Fish to be dried are first left to fermentslightly in pottery or metal vessels or even in a hole in the ground.After this fermentation, the fish are placed flat on a surface exposedto the sun and a (natural or artificial) preservative is added toprevent insect infestation. Apart from the small internal trade circuitswithin the delta itself, most production is sent to the city of Mopti,and from there it is distributed to the rest of Mali and even to someneighboring countries, mainly the Ivory Coast and to a lesser extentBurkina Faso and Ghana, which was until recently the main client.

In Lake Nasser, the situation is very different. This lake wascreated when the Aswan Dam was built on the Nile River. There has alwaysbeen fishing activity on the Nile, but on the stretch now occupied byLake Nasser the increase in catches has been spectacular. The catchincreased 24-fold between 1966-1977 (from 750-18,000 tons). Thefisheries are based on 15 species. Tilapias (Sarotherodon niloticus, S.galilaeus), which like all plankton-eating fish have increasedspectacularly in number and size, are the most abundant, followed bycharacins (family Characidae) such as Hydrocynus forskalii, Alestesnurse, A. dentex, A. baremose) and the Nile perch (Lates niloticus).

Hunting activity

Large-scale hunts are still organized in some Saharan countries forpotentates from the oil-producing Arab countries who can no longer huntantelopes, gazelles, and bustards in their own countries. Yet, mosthunting is due to the perception--deeply rooted among nomadicherders--that wild herbivores compete with their herds and thatcarnivores threaten them. The scarcity of resources in the desertregions of Africa and much of southwest Asia means that hunting is asignificant complement to the economy of many families.

Unlike the precarious subsistence of most countries of SaharanAfrica and the Sahel, in southern Africa there are more than 100,000[km.sup.2] of game farms, large estates where wild animals are raised inthe wild but managed to some degree with the intention of hunting themfor several purposes: meat production, big game trophy hunters, photosafaris. There are also large areas dedicated to intensive or extensiveostrich rearing. The fauna thus plays a major role in the economy--muchgreater than in the countries of eastern Africa such as Kenya andTanzania. Parks represent 5% of the area of southern Africa, but gamefarms represent 8.3%, though not all are in desert or subdesert areas.In Namibia, for example, there are about 400 game farms, most of themwith an excellent management of their animal populations, and theyoccupy almost 25,000 [km.sup.2]. Almost all of them combine wildlifemanagement with the exploitation of domesticated livestock.

The domestication and rearing of the ass

The deserts near the major centers of civilization of antiquity,Egypt and Mesopotamia, were the site of the domestication of two of themost important species of animal whose muscle power has long providedhumans with additional energy to plow the ground, transport heavy loads,and sometimes aid in war efforts: the ass and the dromedary.

The ass (Equus asinus) is the only domesticated large mammaloriginating in the African continent. It comes from the deserts of Egyptand Libya. Its wild ancestor was probably the Nubian wild ass (E. asinusafricanus), which now seems to be extinct, although in some areas(Somalia, Maghrib) it may have been involved in the domesticatedoffspring of other wild subspecies of ass. The domestication of theNubian wild ass seems to have occurred in pre-dynastic upper Egypt morethan 5,500 years ago. Some rock carvings in the western Egyptian desertdated from the Gerzean culture (about 5,500 years ago) support thisidea, and relief carvings on slate tablets from a period soon afterward(Naqadah II, about 5,400 years ago) confirm it. The ass was the mostimportant beast of burden for the ancient Egyptians; all their landtrade was based on caravans of asses. It was only rarely used as amount, and if used to transport people this was done with a sort of bedor chair suspended from two asses harnessed side by side. The ass spreadfrom Egypt to all the areas that traded with the Egyptians, fromEthiopia to Mesopotamia and Iran. Later, in the Roman period, the assspread throughout the Mediterranean Basin and much of Europe and to theedges of the Roman Empire.

The introduction of the domesticated ass into Mesopotamia, wherethere was another member of the horse family, the onager (Equus hemionusonager), led about 5,000 years ago to the first attempts athybridization. The results were good, as the hybrids were stronger andmore resistant than their parents. They were further improved uponlater, when the onager fell out of favor and the asses were crossed withhorses to produce mules, animals the size of a horse and with thestamina and strength of the ass. Mules are the most widely used workinganimals and beasts of burden in much of the world. The colonization ofthe Americas was a new opportunity for asses and mules, which were themost efficient means of transporting heavy loads over long distances onbad roads. Catalan stud asses were particularly successful and helped tosupply mules for most of Spanish colonies, and during the nineteenthcentury they also played an indispensable role in the conquest of thewest in the United States. Throughout the twentieth century, themechanization of transport has displaced horses and their relatives asdraft animals or beasts of burden except in very inhospitable regions orsteep areas, where asses and mules are still extremely useful.

Though available statistics are unreliable, throughout the worldthere are an estimated 40 million asses (more than 10 million of them inChina and about as many in Africa) and about 15 million mules (aboutfive million in China, more than three million in Mexico, and about twomillion in the countries of the Andes and Central America). Despitepopular opinion in developed countries, the number of asses isincreasing, especially in Africa, where the use of animal traction fortransport and agricultural work is, in many areas, an innovation whencompared to agricultural practices using no energy inputs other thanhuman labor.

The domestication and breeding of the dromedary camel

The ass was domesticated in Egypt and then spread to Asia, but thecommon camel or dromedary (Camelus dromedarius) was domesticated insouthern Arabia. It spread westward from there to Africa and east to thehot deserts of Iran and the Indian subcontinent. The dromedary wasdomesticated 5,000-6,000 years ago and led in the following centuries tothe appearance of nomadic pastoralism based on camels as a means oftransport and as a mount, a lifestyle still followed by the Bedouins.Northward migration by Semitic nomads introduced the domesticateddromedary into Mesopotamia and Palestine 3,000-4,000 years ago. TheAssyrians rode camels into battle, as shown in several reliefs of thepalace of Ashurbanipal in Nineveh, which is about 2,700 years old. Thecamel seems to have been introduced to Africa around the time when Egyptwas conquered by Ashurbanipal, arriving not only from the north with theinvading armies but also from the south accompanying immigrants from theArabian Peninsula, though it does not seem to have spread widely throughAfrica's Mediterranean coastline until the Roman period. Thecamel's spread to Iran and India was very slow, too, although thePersian emperors incorporated nomadic camel-riding Arabs into theirarmies from 2,600 years ago onward. Herodotus mentions how the camelswere kept at the rear because their smell frightened the horses, thoughthis was also sometimes used to break the enemy cavalry. Camels do not,however, seem to have reached India until the Arabic invasion in theeighth century. In the fifteenth century they were introduced by Spanishcolonists into the Canary Islands, then into Peru in the sixteenthcentury, but it was only successful in the Canary Islands. In themid-nineteenth century they were introduced into the deserts of thesouthwest United States and Australia.

Some nomadic herders in the Sahara and the Arabian Desert livemainly by raising camels. The Moors of Mauritania, for example, graze anarea of half a million [km.sup.2] (about twice the size of the state ofMichigan) between Jbel Bani Mountains and the Adrar Oasis, more than 620mi (1,000 km) apart, with more than 40,000 head of camel. Normally,however, camels are an essential help to nomads whose herds consist ofother animals or are used as transport (almost one-third of alltrans-Saharan transport is still on camel back). Camel milk is alsoconsumed. The world's camel population is not very large, littlemore than 1.5 million animals, a million of them in Africa and almosthalf a million in Somalia alone.

3.2 Stockraising activity

Livestock production systems in the African hot deserts, the hotdeserts where agricultural and stockraising activity is most intense,include nomadic pastoralism and seasonally migrating stockraising,mostly of camels and small livestock (sheep and goats) and occasionallycattle. These animals drink water from rivers with sources outside thedesert, as in the Danakil Desert. Transhumance is the name for seasonalmovements between the desert and the subdesert or between low areas andthe mountains, while nomadic pastoralism is based on random movementsdepending only on the rainfall. Seasonally migrating pastoralismnormally occurs on the edge of the deserts or in mountainous regions,while nomadic pastoralism occurs strictly within the desert, oftencovering large distances of 620 mi (1,000 km) or more.

Until recently, apart from life in oases, nomadism was almost theonly lifestyle in most of the deserts of Africa and Asia. In the hotdeserts in the Americas and Australia, despite exploiting huge areastotally dominated by sheep, stockraising only requires theshepherds--not the entire population--to travel.

In general, as pastures become increasingly degraded (especially inAfrica and Asia), the percentage of cattle and sheep declines and thatof camels and goats increases. The consumers of woody plants increase atthe expense of consumers of grass. Certain eastern African ethnic herdergroups (Rendile, Samburu, Booran) have adapted their tradition of cattleraising to raising camels.

Northern Africa

In the arid areas of northern Africa, stockraising is restricted tosheep, goats, and dromedaries. There is hardly any cattle in unirrigatedarid zones. Since the 1970s, raising sheep has developed into a form ofspeculation that is highly dependent on subsidized feeds and grains, andthe sheep are increasingly fed stubble, straw, and agricultural and foodindustry residues. The raising of dromedaries is clearly declining,while that of goats is stagnant. The infectious diseases that affectedthe livestock have disappeared thanks to vaccinations, leaving onlyparasitic infections such as infections of the lung and stomach(strongyloidiasis) caused by strongylid nematodes or tapeworminfestation caused by Taenia.

Average consumption of meat is about 40 lb (18 kg) per person peryear, half of it commercially raised poultry. Poultry consumptionincreased from zero in 1960 to 750,000 tons in 1990, growing at aconstant rate of 7% per year for 30 years. Beef and lamb production perperson has remained stable, and so has the sheep/human ratio, at onesheep per person. This ratio has stayed stable for the last 50 years,though total consumption of meat per person has doubled over this time.Production per person of beef and lamb together is about 8.5 kg/year,and that of poultry is about the same.

The Sahel

In 1990 the livestock population of the Sahel countries was about55 million Tropical Livestock Units (TLU), after almost tripling in thelast 40 years. Cattle account for about 60% of the biomass of livestock.Stockraising used to be limited regularly by the death of many animalsdue to infectious diseases, especially rinderpest, contagiousperipneumonia, anthrax, brucellosis, epizootic abortion (vibriosis), andfoot-and-mouth disease. These sanitary constraints have largely beensolved by a vigorous preventive program, especially vaccinationcampaigns.

Diseases transmitted by ticks are not a major problem in the Sahel,unlike in eastern Africa, probably due to the extreme dryness of the airfrom November to May, which prevents these arachnids from reproducing.All this has led to the exponential growth of the number of head ofcattle, at a rate of 2.2% per year. Traditional pastoral practices,virtually unchanged apart from these sanitary improvements, have changedlittle, and pastures have been greatly degraded by the increased numberof cattle, plowing, and competition for land between stockraisers andfarmers. The rearing of small ruminants (sheep and goats) is restrainedby an as-yet incompletely understood disease, small ruminant plague, andalso by parasitic infections of the respiratory or digestive tracts.

Livestock productivity is very low in the Sahel, especially due tofeeding problems and traditional stockraising practices. The main directcauses for this low productivity are: the long time between births, lowfertility, the low percentage of reproductive females, the highpercentage of males, inadequate and unbalanced feeding, parasiticinfections, and diseases.

Eastern Africa

In 1980 eastern Africa contained about 78 million TLU and had ahuman population of 110 million (0.7 TLU per person). The constraints onstockraising are the same as those in the Sahel, though there are somedifferences. Fodder availability is slightly better, as there are tworainy seasons a year; therefore, fresh food is available for more of theyear and the animals' diet is more balanced. There are, however,two factors that are less favorable than in the Sahel: disease and thethreat of predators.

One major group of livestock diseases are the different forms ofpiroplasmosis (or babesiasis), parasites that destroy the red bloodcells. They are piroplasmids (protoctists of the apicomplex group, alsoknown as sporozoans) transmitted by ticks. East Coast fever, caused bythe piroplasmid Theileria parva, takes the form of long periods (15days) of high fever, followed by an apparent improvement, and then thecattle's sudden death due to lung edema; cattle tick fever causedby Babesia bigemina destroys the red blood cells, leading to symptoms offever and blood in the urine. Other diseases transmitted by ticksinclude anaplasmosis, which is often fatal and is caused by Anaplasmamarginale, an aphragmabacteria or mycoplasma that takes the form offever, jaundice, and intense destruction of the red blood cells, whichshow a characteristic sickle shape. There is also the rickettsiainfection known as heartwater, caused by Cowdria ruminantium. Thesetick-transmitted diseases are prevented by anti-tick baths and dusting.

Predation by large carnivores (lion, laughing hyaena, jackals) is asecond problem that is worse in eastern Africa than in the Sahel, aspredators may locally take 10% of the herds, mainly the young animals.Unlike the Sahel, eastern Africa has a modern productive livestocksector, but not in the arid area, which is entirely dedicated totraditional grazing and whose productivity is comparable to that of theSahel.

Southern Africa

Unlike the other arid zones of Africa, stockraising in southernAfrica is highly diverse, mainly sedentary, and extensive, but at thesame time modern and commercial. The tropical savannahs of Botswana,Namibia, and the Transvaal are essentially used for cattle ranching,while the grasslands of the Karoo and Namibia are dominated by smallruminants, especially sheep. The total herd in southern Africa is about31 million TLU, of which about 50% are located in the arid zones (sensulato). Of this total, cattle represent about 70% in terms of metabolicweight (1.7 lb [0.75 kg]), sheep about 22%, and goats about 8%. Thenumber of cattle represents 30%, sheep 54%, and goats 16% of the totalnumber of head of livestock.

The cattle of southern Africa are heavier than the average Africanzebu (1.2 TLU/per head); a high proportion are animals for fatteningthat belong to selected breeds such as the local Afrikaner zebu cattle,or the Indo-Pakistani brahman zebu, or are the product of a variety ofcrosses (for example, Afrikaner crossed with humpless cattle of Europeanorigin and the bonsmare breed, or Afrikaner crossed with short-hornedDurham). In Botswana and Namibia, the tswana and its crosses are thedominant breed. The breeds of zebus (Bos taurus indicus) and crosseswith humpless breeds, mainly of European origin, are a necessity, giventhe zebu's relative tolerance of tick-borne diseases likepiroplasmosis. There are three main breeds of sheep: merinos for wool,dorper for meat, and karakul for leather, of which South Africa has theworld's second largest flock. There are two main breeds of goat:the Boer goat, a large, robust, animal reared for its milk and flesh,and the Angora goat, which produces mohair wool.

Southwest Asia

Stockraising in the Arabian Desert is similar to the model in theSahara, with nomadic Bedouin stockraisers who raise herds of sheep andgoats. Farther north and east, from Anatolia to India, high-altitudenomadic stockraising is more common, and this exploits the mountainpastures in the summer and those of the subdesert plain in the winter.This is similar to seasonally migrating stockraising, but in this casethe entire community moves. The Paichu nomads of Afghanistan, who travelfrom the Indus Valley to the peaks of the Hindu Kush with thousands ofhead of sheep, goats, camels, asses, and horses, are perhaps the mosttypical example. Turkey, Iran, and India have the largest number ofsheep in the area, 35-55 million each; only Australia, China, and NewZealand have more. Pakistan has the largest number of goats, with 25million head (exceeded only by China), followed by Turkey and Iran with15-20 million head.

The North American and Argentine deserts

Dominated by extensive cattle ranching and sheep raising, the NorthAmerican deserts are an extension of the high prairies of the plainseast of the Rocky Mountains. Sheep dominate in New Mexico, where theNavajo have become the most important raisers of sheep, while cattledominate in northern Mexico and in Arizona, where varieties of Britishorigin have replaced the former criollo cattle even on large estates inMexico. They are essentially raised for their flesh, which is fattenedlocally, or they are bred to be fattened in farms elsewhere. Onedistinctive feature, especially in Mexico, is the relative abundance ofhorses and their relatives, with more than four million horses, almostthree million asses, and nearly three million mules.

The Argentinean monte is an area of extensive stockraising, mainlyof sheep, but also of cattle, in large estates enclosed by wire fencing.Though they are not as large as the huge sheeprearing estates ofPatagonia, they are still very large, often owned by stockraisers ofBritish origin, who have replaced the merino with British breeds thatproduce wool (Romney Marsh) or flesh (Lincoln). Cattle are bred in thearea but tend to be fattened in the wetter pampas regions.

The Australian subdeserts

The large sheep raising areas are not so much in the deserts andsubdeserts as in the savannah and prairie regions, though they partlyaffect the subdesert regions surrounding the central deserts, which aretoo inhospitable for any type of stockraising activity. In thesesubdesert areas, the main stock animals are merino sheep raised fortheir wool. They graze extensively in large herds. The low productivityof these pastures means that more than 5 ha (1 ha=2.5 acres) is oftenneeded to support a single animal.

4. Management conflicts and environmental problems

4.1 The human contribution to desertification

The desert biome, unlike all the other biomes, seems to beexpanding. This is due partly to climatic factors, but, as has alreadybeen pointed out, it is also due to thousands of years of human actions.Two centuries ago, the romantic French writer FrancoisAuguste-Rene deChateaubriand (1768-1848) wrote: "Forests precede people, butdeserts follow them." Perhaps this is not always true, but itexpresses very clearly the decisive role of human beings in spreadingthe world's deserts.

Like the sea, deserts are commonly but wrongly thought to be alimitless dumping ground. One major difference between them, however, isthat in the sea, wastes are dispersed by waves and currents; in deserts,they are only dispersed by the wind. What is dumped in the desert and isnot gradually blown away by the wind stays there, or--if the substrateallows it--seeps down to contaminate the aquifers. These hard facts donot prevent many people from considering deserts as ideal sites toinstall or dump anything and everything that may be bothersome ordangerous, including contaminating industrial waste, radioactive waste,and garbage from secret military installations and nuclear test sites.Much of the industry recently established in many petroleum-exportingcountries (Saudi Arabia and Libya), or that which has recently grown upin connection with mining (such as that of phosphates in Morocco and, toa lesser extent, in Tunisia), is highly contaminating. In theoil-producing countries, it is mainly the petrochemicals industry,although there is a desire for some diversification by adding otherindustries to make use of several locally available raw materials (forexample, iron and steel works in Saudi Arabia and Libya). In Morocco andTunisia, the emphasis has been on phosphate fertilizer production, oftenin industrial plants that do not fulfill the minimum conditions demandedof similar industries in developed countries.

The uncertain effects of the current climate change

The currently available global atmospheric circulation models(about 20 have been proposed in the last 15 years) have definedhypotheses about climatic change due to the increasing levels of carbondioxide and other pollutants. All these hypotheses foresee, with somedifferences, an increase in the global temperature of 3-5[degrees]C inthe lower atmosphere by 2050. This increase would not be hom*ogeneous butwould increase with latitude by 0-1[degrees]C at the equator and by6-9[degrees]C at the poles. Yet these hypotheses disagree on the changesin rainfall patterns; some envisage a small increase in rainfall at thelatitude of the arid regions, while others predict a slight decrease.

In the worst foreseeable case for the hot deserts, given that atemperature increase of 1[degrees]C causes an increase in the potentialevapotranspiration of about 70 mm/year (i.e., an increase of 2-7% in thearid areas) and supposing that rainfall did not vary, then the rainfalleffectiveness or precipitation/evaporation index (P/PE) would decline inthe hot arid areas by about 4-5% per [degrees]C increase in temperature.The climate would thus get worse: aridity would increase. The increasein temperature would also cause a shift to more thermophilouscommunities in the vegetation at given latitudinal and altitudinalzones.

Obviously, these changes will not be sudden. Paleontology andpalynology show that a rapid change can occur in a century or even less,while a slow change may take a thousand years. There will thus be anindeterminate delay between the predicted physical changes and thebiological responses to them. This delay would depend on the capacityfor change of the ecosystems, an aspect that has not yet been thoroughlyinvestigated. It is, however, generally considered that this ability torespond is low. It might thus be expected that rapid changes would occurover a period of a few decades, and that these changes might be locallyslowed down or speeded up by climatic fluctuations (periods withrainfall greater or lower than the long-term averages).

In the worst case, the bioclimatic zones might be displaced byabout 10% toward the neighboring, more arid areas. Thus, within a periodof 50-100 years, the hyperarid area might spread to cover 10% of thearid zone, the arid zone might spread to cover 10% of the semiarid zone,and so on. This hypothesis is far from being confirmed, as somephysiological mechanisms tend to attenuate the impact of these changes.In the first place, the increasing CO2 concentration in the atmospherewould cause a carbon fertilization effect because photosynthesis wouldbe increasingly effective. Carbon fertilization caused by a doubling ofcarbon dioxide in the atmosphere to 700 ppm by volume by the year 2050might cause an increase in primary production of 10-30% (the combinedresult of simulations carried out in greenhouses or growth chambers) orperhaps only 8-10% (the combined result of open air experimental data inair enriched with carbon dioxide). The increase in atmospheric carbondioxide will tend to decrease stomatic conductivity, thus reducingtranspiration and water consumption by 10%. Current knowledge does notallow us to say which mechanism will prevail, the increase in theclimatic demand for water (potential evapotranspiration) or the savingof water due to the lower stomatic permeability and the increasedphotosynthetic efficiency.

The inevitability of human desertification

Whatever the consequences of the climate changes, people are themain cause of recent desertification. A prolonged drought is neithernecessary nor sufficient to start desertification. Climatic variabilityis one of the characteristic features of the arid lands, and there aremany convincing examples and much evidence that natural ecosystems canresist a prolonged drought with almost no damage, as long as the impactof human beings and their herds of livestock is slight. When subject toa moderate grazing pressure (measured in terms of their carryingcapacity), the pastures of the Sahel, for example, can resist droughtsof up to 15 years without major alterations, despite the apparentcontradiction that millions of hectares of overgrazed land have becomedesertified.

Desertification can start (and has in many cases started) inperiods of moderate aridity--and even in periods that are less arid thanaverage. All that is necessary is for the fragile and unstableecosystems in question to be subject to especially intense pressure frompeople and their animals. In the best of cases, the native perennialspecies are replaced by annual plants or perennial weeds, unpalatable tothe livestock and useless to human beings except as protection fromerosion for the soil surface. In the worst case, the elimination of allthe plants leaves the soil totally bare and subject to the uncheckedaction of the agents of erosion--the impact of the drops of rain, theforce of the freshets (that are no longer slowed down by thevegetation), the wind and the particles it bears, etc.

Anthropogenic desertification--the apparently irreversibledegradation of a relatively arid space to conditions of little or nobiological production (bare soil, sand dunes, rock pavements) as aresult of human intervention--affects immense areas of the planet,according to the most reliable calculations. About 60,000 [km.sup.2] ofarid land turn into deserts every year. On the northern edge of theSahara, an estimated 0.5-0.7% of the area of arid land turns into desertevery year. These figures are considerably lower in the North Americanand Australian deserts, but they do not escape this scourge entirely.

The impact of the various ways that humans degrade the soil andvegetation in the world's arid areas varies greatly from one areato another with the standard of living and lifestyles of their humanpopulations. Two main activities--the cultivation of subdesert steppeand scrub for dry farming, and deforestation due to firewood collectionand charcoal production--are typical causes of deforestation in ruralsocieties with low incomes or with very high rates of population growth.They mainly occur in developing countries in northern Africa, the NearEast, the Sahel, eastern Africa, and the Indian subcontinent.

Other equally dangerous activities, including the destabilizationof sand dunes by fourwheel-drive vehicles, some types of touristdevelopment, urban and industrial pollution of air, water, vegetationand soils, as well as uncontrolled fires, are more likely to occur insocieties with high incomes.

Some activities that have an effect on the overexploitation ofresources may be shared by poor countries (where much of the populationlives in arid areas and depends on the meager resources for survival)and by rich countries (where only a very small percentage of thepopulation lives in the arid areas and is only marginally dependent onthe resources). Overgrazing is an example: in most (but not all)developing countries, high grazing pressure coincides with a highpopulation density, leading in turn to some of the other destructiveactivities described above. However, high, and even excessive, stocklevels may also occur in countries without this demographic pressure(United States, Argentina, Australia). Rich and poor countries alsoshare extractive activities whose location depends only on the locationof the mineral deposits, but they receive very different treatments,depending on the environmental legislation in a given country. The waythat rich countries and poor countries cause desertification may bedifferent, but the end result is always the same: more desert.

4.2 The impact of wild-gathering

The current climate change is not the first to affect the hotdeserts in the last few millennia. There is plenty of evidence thatpeople used to live permanently in areas that only nomads now visit (andonly seasonally); humans even lived in some areas that these nomads nowavoid because of their extreme aridity.

The hot deserts we know have formed gradually over the last 10,000years, independent of human pressure, which was relatively moderatebefore the expansion of irrigated agriculture (initially only inMesopotamia and Egypt) and the spread of nomadism that followed thedomestication of the camel. There are also testimonies of anthropogenicdesertification; dune fields or salt pans in areas that were oncecultivated, cities buried under the sand, and networks of channels thathave silted up and are now dry.

From balance to risk

In the desert, gathering resources requires a great deal ofknowledge. The Aboriginal tribes of Australia's desert regions wereperhaps the pre-Neolithic human group best adapted to life in hotdeserts because of their exact knowledge of the area's resourcesand their ability to use them over the seasons of the year.

The Walpiri (or Walbiri) are one of the best-studied cases. Theyused to live in a desert region in the southwest of the NorthernTerritory, near its border with Western Australia, and did not come intocontact with the British colonists until the second half of thenineteenth century. Throughout the year, the Walpiri traveled throughouttheir territory hunting and gathering all sorts of animals and plants.

Their use of the flora and fauna was quite remarkable, and theirdiet consisted of more than a hundred animals and about 40 plants. Inautumn, when the springs were full and the game and edible plants wereabundant, they came together in large groups and moved leisurely fromone spring to the next; as the water became insufficient for the entiregroup, the group subdivided and dispersed into smaller groups until thespringtime. When the resources had declined to a minimum and life wasgetting difficult, the groups were split up into single family groups.During this period, their thorough knowledge of the way of life of allthe organisms they ate allowed them to find roots, tubers, or lizardshidden underground. Only in cases of exceptional drought was any groupleft totally without any resources, and then they had to cross thefrontier of the neighboring tribes, whose lands had more resources,rather than die of starvation.

An exceptional drought from 1924-1927, 50 years after the Walpirihad come into sporadic contact with the colonists, caused the survivingWalpiri to disperse; most settled in the region of Alice Springs and ondifferent cattle ranches.

The increasing consumption of firewood

About 90% of the energy needs of most of the peoples living in thehot deserts and subdeserts are met by firewood extracted from the fewtrees and shrubs that grow locally; all traces of woody vegetation havenow disappeared in a radius of 4-8 km (19-77 mi2 [50-200 [km.sup.2]])around most villages in the Sahel.

International organizations estimated the average rate ofdeforestation for the period 1981-90 was about 0.7% per year. This ratecorresponds to a reduction of 10% of the area covered in 15 years, 20%in 30 years, 30% in 50 years, 40% in 70 years, and 50% in 100 years (alogarithmic regression). But the rate of deforestation is growing inparallel with the increasing population (2.7% per year), so the chancesare that the entire Sahel will be almost totally deforested by themiddle of the twenty-first century.

There have been some remedial measures, such as the localintroduction of cooking fires with a greater energetic yield than thetraditional simple fire on the ground between three stones. Still, theyare insufficient, despite surprising success on a local scale. (In theAgades Department of Niger, an estimated 600 trees a day have been savedby the spread of these simple devices.)

In a similar manner, but in clearly different social and economicconditions, overexploitation of the patches of algorrobales in theArgentinian monte (phraetophytic thickets of Prosopis flexuosa, known asalgorrobo dulce to the Argentinians) has made this species rare. It isfelled for timber for building houses or service buildings on cattleranches, to plant vineyards, and of course for fuel. Mining uses timberfor construction and firewood for fuel and has also been highlydestructive in the monte, as well as in many other deserts.

In the deserts of northern Chile, the indiscriminate use of thevegetation by the mines since colonial times and by contemporary humansettlements has been one of the causes for increasing desertification.In the last 20 years, intense state-funded efforts have been made toreverse the loss of plant cover by creating artificial plantations ofdifferent shrub and tree species, both native and introduced, of thegenera Prosopis, Acacia, Atriplex, and Eucalyptus.

In some regions, western Africa among them, gathering medicinalplants and other useful plants may, like gathering firewood, lead to thedisappearance of the woody plant cover that protects the soil fromerosion and supplies it with organic material.

4.3 Minimal agriculture

Though it may seem incompatible with the current climaticconditions of the deserts and subdeserts, most of the Neolithic centerswhere humans first practiced agriculture were located very close to theedge of arid regions. The secret of their success was almost alwaystheir use of an additional resource, water, which is vitally importantin deserts.

Water is the limiting resource in the world's arid andsemiarid regions, as it is absolutely essential for life and has manyother uses (drinking water, sanitation, irrigation, transport routes,industrial uses, treatment--or simply transport--of sewage). Watermanagement, including management of surface waters, underground waters,and rainfall, leaves much to be desired.

Water exploitation systems can, however, easily turn into adouble-edged weapon: they may become a curse rather than a blessing,especially if proper preliminary studies are not performed, if usage andmanagement rules are ignored, or if the legal provisions are unrealisticand thus not enforced.

In some areas, water is not necessary, as the low rainfall, or eventhe fog, is sufficient. This is shown by the techniques of the ancientNabataean culture, now successfully copied in the Negev Desert, based oncapturing the runoff water from a large area; similar methods have beensuccessfully developed in the northern Sahara and in the Sonoran Desert,where the Papago Indians excelled at this type of agriculture. In thearid coastal regions of Peru and Chile, which are frequently covered byfog, ingenious devices with large condensation surfaces are used toobtain significant quantities of water from the fog.

Subsistence dry farming

Very few of the hot deserts are fortunate enough to receive heavycondensation. In many of the world's subdeserts, the naturalvegetation is being destroyed, partly for the establishment ofsubsistence crops, especially cereals that are on the borderline ofviability.

The reasons for this senseless agricultural activity lie in povertyand population pressure, as the population of these relatively poorregions has been growing exponentially for the last half century, andthe legitimate desire for increased income or the need to feed a largefamily stimulate this type of agriculture.

This is subsistence, or even survival, agriculture. These extensivecrops are cultivated with very low inputs, without fertilizers orpesticides, and no more labor than plowing and sowing with a discharrow; the amount of seed used is very low, only about 30-50 kg/ha forbarley, and so the crop obtained by the farmer is about 200 kg/ha ofgrain (while in commercial cultivation, the yield is 1,000-1,200 kg/haof grain). Thus, any grain production above 200 kg/ha is profitable.

Yet not even this small yield is reliable. In the subdesertwastelands and scrubs of northern Africa, which since the Second WorldWar (1939-1945) have been subject to episodic exploitation of this type,the chance of obtaining a harvest is 10-40%, and when there is a harvestit may range from 100-1,000 kg/ha of grain.

The most widely cultivated grain is barley (Hordeum vulgare) andthen durum wheat (Triticum durum). Despite the unreliability of theharvest and the low yields obtained, cereal crops and the associatedfallow ground represent 30-50% of the area of the wastes and scrubs ofnorthern Africa. To put it another way, all the soil soft enough to beworked, except dunes and excessively saline soils, are cultivated in theagricultural years when the autumn rains are favorable. The result is anauthentic ecological catastrophe: soil erosion, the formation of largeareas of sand dunes, and desertification.

Large areas are cultivated sporadically in favorable years (theseoccur anywhere from one year in three to one year in ten) and may cover60-70% of the surface area of the subdeserts of some parts of northernAfrica and the Near East. In other areas such as the Sahel, easternAfrica, and the edges of the Kalahari, degradation is equally clear, butthe area affected is smaller.

Barley is the most widely cultivated cereal in the Mediterraneanedges of the Old World deserts, but on the tropical edge of the desertsof both the Old World and the New World the commonest cereals are pearlmillet (Pennisetum glaucum) and sorghum (Sorghum bicolor).

These randomly grown crops are present even in the arid areas ofdeveloped countries (United States or Australia) but do not evolve. Indeveloping countries, as the population expands, larger areas of groundhave to be cultivated to obtain sufficient food; if there is no moreland to clear, the fallow period is shortened or eliminated, thusreducing the fertility and therefore the yield, so that larger andlarger areas are needed to obtain the same harvest. This worrying spiralof desertification is self-accelerating.

In many countries, especially in the Sahel, laws have been passedbanning the plowing of land in areas with rainfall below a definedannual average (normally 14-16 in [350-400 mm]), but these laws are notenforced. Niger, as part of its policy to preserve natural resources,passed laws in 1961 and 1962 establishing a northern limit to dryfarming (the 16 in [400 mm] average annual rainfall isohyet).

North of this limit, an area was established exclusively forlivestock exploitation, and laws were also passed to regulate theherders' use of wells and other water points; the governmentregulated vaccination campaigns and prevented the burning of scrubaround the new wells that had been dug, thus establishing crucialelements of livestock policy; Niger also created a new public-sectorbody responsible for monitoring wells and enforcing national livestockpolicies. This law fixed a northern limit to dry farming, but it wasnever applied; in fact, millet cultivation spread farther and farthernorth, to the 10 in (250 mm) and 8 in (200 mm) isohyets, even in themajor drought that began in 1969. The farmers lack training, and theirdesperate need to grow the food they eat leads them to overexploit theland.

The salinization of irrigated ground

Desert agriculture relies on irrigation, either with surface watersor underground water. Yet even this form of agriculture has itsproblems; desertification can also be started by incorrect use of waterresources. There are about 250 million ha of irrigated land in theworld, and roughly 0.4-0.6% of this area is lost every year, becomingunproductive or completely sterile due to excessive salinization,sodication, or waterlogging.

If they continue at their present rate, in 140 years one-half ofall the land currently irrigated will become unproductive. This wouldhave disastrous effects on the world food production, as irrigated landis the most productive. (Though it only represents 18% of all cultivatedground, irrigated land produces one-third of all humanity's foodand therefore benefits from investment of up to $20,000 per hectare.)

Some traditional irrigation systems have shown themselves to bevery efficient and sustainable. Egypt, for example, lived for thousandsof years by its agricultural irrigation based exclusively on the regularflooding of the Nile, until little more than a century ago, when thefirst major hydraulic transformations were put in place. The inlanddelta of the Niger contains the most important concentration ofa*griculture in the Sahel. On the Pacific coastal slopes of the PeruvianAndes, there are series of terraces surrounded by marls on which cotton,alfalfa, sugar cane, and maize are grown. In this area, most of thenative vegetation, including the Prosopis thickets, has been felled fortimber and for charcoal and has been replaced by small plantations ofolives, pears, apples, and plums; all that remains, shading the edges,are a few specimens of willow (Salix humboldtiana), pepper tree (Schinusmolle), and the reed jabonero or uva grass (Gynerium sagittatum). Someambitious projects seek to channel water from the upper slopes of theAndes in order to extend the area of agriculture in the region.

The undesirable consequences of irrigating arid areas are by nomeans new. The ancient Sumerians had problems of salinization due totheir crops' intense evaporation in the summer, and by 4,000 yearsago the previously balanced proportion of wheat to barley started toswing heavily in favor of barley, which is more resistant to salt. Wheattotally disappeared within a century, while the yield of barley per unitarea diminished 4,0003,500 years ago. These changes were related to thegradual movement northward of the centers of power in Mesopotamia, andthe region's definitive decline with the fall of Babylon to thePersians 2,600 years ago. The Persians renovated the irrigation anddrainage network, but only in conflict-free periods of highlycentralized power did it function regularly. When the Sassanid dynastycollapsed in the face of the Arab advance, this network had deterioratedgreatly due to silting up of the channels. The thirteenth century Mongolconquest ended the legendary wealth of Mesopotamia, which it has stillnot totally recovered.

Secondary salinization may be due to several causes. Excessivelysaline soils are unsuitable for irrigation due to their bad drainage, asare those that have unbalanced proportions of cations. But soildegradation is often due to incompetent management, lack of maintenanceof drainage systems, excessive irrigation, or the application ofinappropriate agricultural systems. The most frequent cause isinadequate drainage for whatever reason (because it was not included inthe preliminary studies, because adequate drainage was not built to saveon investment, because the project was badly planned from the beginning,or because it was never brought into operation in order to save money).Furthermore, instead of low levels of salinity, the water used may havean unbalanced cationic composition.

Salinization affects a very large area: 4.5-9 million ha inPakistan, 15 million in India, 750,000 in Egypt, and 4 million in theUnited States. An estimated 5% of the 5.2 million [km.sup.2] of aridland that have become desert did so because of salinization. Theselosses are the most important economically, as they are potentially themost productive areas in the world.

Large hydraulic schemes

The twentieth century has seen many drastic transformations in thelongest-lasting of all irrigation systems, the traditional Egyptiansystem. The construction of the Aswan High Dam, which retains theimmense Lake Nasser, makes it possible to regulate the flow of the Nile,without surges or droughts, and to supply water year-round to the twomillion ha of preexisting irrigated land in Egypt, as well as to anadditional 500,000 ha (1 ha=2.5 acres). Much of this land produces morethan one harvest a year, which is very necessary in a country with oneof the world's highest rates of population growth. The Aswan HighDam, like almost all the large dams built since the late nineteenthcentury, not only meets irrigation requirements but also produceshydroelectric power, enough to meet much of Egypt's energy needs.

However, retention of sediments by the dam (silting) has caused aseries of undesirable problems. The most serious is probably the retreatof the front of the Nile Delta, and attempts are being made to preventthis by building large cement dykes to avoid erosion. There has alsobeen a drastic decline in fisheries, both in the Nile itself and alongthe coastline of the southeast Mediterranean, as well as an increase inthe incidence of schistosomiasis. Flood-derived silt used to provide aregular input of organic matter and minerals for the croplands (nowit's replaced with fertilizers) and was also a source of mud formaking pottery and bricks (but the mud is now taken from good arableland). Furthermore, excess irrigation accompanied by deficient drainagehas created so many problems due to the rising water table and thesalinization of land that, in the mid-1970s, an estimated 80% ofEgypt's cultivated land needed improved drainage.

When the first Spanish colonists reached the lower basin of theColorado, there was already a dry farming tradition among theagricultural Indian peoples living there. The Spanish brought their ownexperience from Andalusia and created new irrigated areas, especiallyalong the Santa Cruz River, a tributary of the Gila, from themid-eighteenth century onward. In 1902, the U.S. government began anambitious scheme to develop the entire Colorado Basin, mainly byproviding urban infrastructure and irrigation throughout the hot desertregions of the lower basin.

The project that definitively changed the river was theconstruction of the Hoover Dam (1928-1935) in Boulder Canyon and therelated schemes (especially the All-American Canal) that allowed theirrigation of more than 642,471 acres (260,000 ha) in southernCalifornia and southwestern Arizona, and more than 395,367 acres(160,000 ha) in Mexico, without summer drops in level or catastrophicsurges. At the same time, the dam can produce 4,000 million kWh(kilowatt-hours) of electricity every year. The Hoover Dam impounds LakeMead, which initially had a capacity of 40 billion m3, almost double theriver's annual volume of flow. It ensured efficient regulation ofthe river, completed by other major dams on the upper basin and a seriesof smaller dams in the lower basin, beginning with the Imperial Dam (thestarting point of the All-American Canal) and some others on theColorado River itself (Davis, Parker, Headgate, Rock, Palo Verde,Laguna, Morelos dams) or on its tributaries (Coolidge Dam on the GilaRiver, Roosevelt Dam on the Salt River). Downstream, the effect of theHoover Dam on the Colorado River (in Spanish, colorado means red, thecolor of the sediments transported by the river) is equivalent, but on asmaller scale, to that of the construction of the Aswan High Dam. Before1930, the Colorado transported an average 125-150 million tons ofsediments (more than the roughly 100 million tons transported into theMediterranean by the Nile before the construction of the Aswan HighDam), but since 1934, when Lake Mead began to fill up, the sedimenttransported fell to minimum values and declined to almost nothing afterthe mid-1950s.

In the 1970s, construction began on the Granite Reef aqueduct tobear water from the Parker Dam to the city of Phoenix and thesurrounding area and to the irrigated fields of the Salt River'svalley. The aqueduct, the first of the schemes in the Central ArizonaProject, was finished in 1986 and supplies irrigation water to more than988,417 acres (400,000 ha) of new irrigated land and more than 600million m3 for domestic, urban, and industrial use in the areas ofPhoenix and Tucson. Use of the Colorado's water has now reached anupper limit that can only be exceeded by very rigorous measures to savewater or to reuse it; there are now more legal disputes in the ColoradoBasin than in any of the world's other river basins.

One feature of irrigated agriculture in the Lower Colorado is thesharp contrast between the Mexican and American sides of the frontier(which is clearly visible in satellite pictures). The American side,where sprinkler irrigation systems have been widely used since the1960s, uses a lot of high technology and is highly productive. Recently,laser leveling and automatic sluice-gate control have been introduced.Unlike in the Nile, the water is not distributed free by the federalgovernment but is distributed by profit-making private enterprises.Water is expensive, so the American farmers of the Lower Colorado haveto seek the most profitable strategy by carefully following marketdevelopments, depending on which they may change crops (sugar beet,long-staple cotton, fodder for penned livestock, etc., though fruit andvegetable production is also important). Even so, there are problems.The spread of irrigation in the Gila Valley since the 1950s hasincreased the salinity of the waters of the Colorado River, which led tolegal claims by Mexico (whose internationally recognized usage rightswere negatively affected) and forced the construction of desalinizationplants. Heavy use of fertilizers and pesticides means that any excess,like the breakdown products, ends up in the rivers or the aquifers.

Irrigation with fossil water

Some oil-exporting countries have decided to invest part of theirhuge profits from oil and gas in huge hydraulic projects to use thelarge fossil aquifers below the Sahara and the Arabian Desert. Thesevery deep aquifers formed in the geological past receive no water atall, and so like oil, they are not renewable resources. The reserves areenormous, with 3,400, 4,800 and 10,000 km3 in the Libyan aquifers ofKufrah, Murzuq, and Sarir respectively.

In 1971, a development project in the Al-Kufrah oasis in Libya toirrigate 24,710 acres (10,000 ha) of cereal crops began the constructionof what has been called the Great Desert River, a huge pipeline made forcarrying water from Tazirbu (in the middle of the desert, about 500 mi[800 km] from the Mediter-ranean coastline) and from Sarir (485 mi [780km]) to the coastal cities of Surt and Benghazi in Cyrenaica. Theproject was completed in 1992. A similar design will bear water from theaquifers of Fezzan to the coasts of Tripolitania and will ensure thefood supply of 300,000 sheep in the north of the Fezzan region. SaudiArabia now also exploits fossil water resources in order to becomeself-sufficient in food production, and surprisingly, since 1990, SaudiArabia has been a net exporter of wheat and other food products.

4.4 Grazing in adverse conditions

The decline of nomadic pastoralism began in the Near East in the1920s with the discovery and exploitation of the first oil fields in theregion. After the Second World War (1939-1945), this decline spread toall the hot deserts in the Old World. In the early 1960s, for example,about 1.75 million people lived as nomads in the 10 countriessurrounding the Sahara. Today, there are only half a million nomads. Incenturies past, the nomads of the African deserts controlled the oasesthat were cultivated by their serfs and slaves; they also controlled thetrans-Saharan caravan trade between central Africa and the Mediterraneancoastline, as well as the salt trade between the central Sahara and theecological zones to the south (the Sudan, Guinea, and Sahel). Theselifestyles have become extinct, except in the case of the Kababish inSudan, who have adapted their activities very well to motorizedtransport. Most of these nomads have been forced to emigrate to thecities and now survive on international food aid, join the army, thepolice, or other government service, or work in the oil fields or mines.

Traditional subsistence nomadic lifestyles have incorporated newways of using pastures, that, as a whole, have even further increasedthe impact of the already poor vegetation of the African and Asiandeserts. On the edges of the desert, especially in northern Africa andin the Near East, seminomadism or transhumance is practiced, combining aprecarious cultivation of cereals that relies on the winter rains withgrazing in the mountains in the summer; in seminomadism, the entire camp(or duar) moves as a collective, but in seasonal migration only theherders travel. Anyway, in the last half century, the number of head ofcattle in the deserts in the developing countries has grown at 1-2% ayear, half the rate of growth of the human population. The area ofgrazing has declined at almost the same rate due to clearance foragriculture, so livestock density has increased roughly fourfold in thelast half century.

Overgrazing around water points

The increase in stock density has not been compensated byimprovements in production techniques and practice, and some moderntechnologies have unfortunately made the problem worse. The drilling ofwells with pumping stations that can supply 4 l/s, paradoxically, in thesubdesert pastures in the Niger Republic, led to the rapid destructionof the grazing within an area of 12 mi (20 km) around these waterpoints, due to the lack of adequate planning and management criteria.

Theoretically, the number of animals with access to the wellsshould be controlled by opening and closing the pumping stations, but inpractice the local representatives of the government were never able tomanage this, and during the dry season many animals concentrated aroundthe wells, perhaps 20,000-30,000 TLU per well for 8-10 months a year,far exceeding (by up to three times) the carrying capacity of thegrazing land.

In this area, the carrying capacity was 8-10 TLU/ha before thewells were drilled, but now it is less than 4 TLU/ha. In an area of 124acres (50 ha) around the wells, the density reached 20 TLU/ha a day. Intwo or three sites, the final result was the destruction of all thegrazing within an area of 12-19 mi (20-30 km) around each well, between126,000 and 283,000 ha (1 ha=2.5 acres). In the extreme 1970-1973drought, the many animals that died next to the wells died of hunger notthirst.

This example shows that a policy designed with the best will in theworld can lead to disaster if it is not based on realistic assessmentsof the situation. But not all the different ways of managing water havehad the same results. The wells drilled in the Ferlo region of Senegal,despite creating some problems, did not destroy the food resources ofthe herds or create an anthropic desert. This was due largely to thefact that the area belonged to a hom*ogeneous group of pastors, the waloor dieri Fulani, who prevented the entry into the area of other herdersand thus converted the area into a forest and grazing reserve.

Throughout the Sahel, free access by livestock to wells and largepools and rivers has, in general, had the same results: the destructionof grazing lands and desertification. The impact on the woody vegetationof the Sahel has been especially well documented by at least a dozenscientists. The woody layer is in most cases declining, by about 1% ayear. In the stockraising areas of eastern Africa, specifically northernKenya, southern Ethiopia, and Somalia, exploitation of water in pools,without any control on grazing, had the same results as in Niger, andthe several million dollars invested by the World Bank had the sameeffect.

Agro-pastoral degradation of oasis margins

Likewise, irrigated areas are often surrounded by a strip ofextremely degraded arid land-land degraded by dry farming, permanentgrazing, or firewood collection.

The money obtained from irrigated crops is usually invested inlivestock that graze freely in a radius of 3-4 mi (5-6 km) in the caseof small animals and 12-16 mi (20-25 km) in the case of cows and horses,the distances these animals can travel in a day while grazing.

A study was performed on the periphery of the central zone of theinland delta of the Niger (see map on p. 237) in Mali; comparison of twosets of 1:50,000 aerial photographs taken in 1952 and 1975 showed thatduring this period, the area of intensely degraded ground increased fromless than 200,000 ha to 1.2 million ha, from 4% of the area in questionto 26%. During the same period, the area dedicated to dry farmingincreased from 130,000 ha to 255,000 ha, almost doubling to 5.5% of thearea.

Many recently developed irrigation systems have also caused similardegradation of their surroundings, but the old oases remaining in thenorthern and southern Sahara have probably been surrounded since timeimmemorial by dry zones, just as they were described by latenineteenth-century and early twentieth-century explorers.

4.5 The exploitation of mineral resources

The hot deserts and subdeserts contain many mineral resources. Inmany desert areas, minerals are by far the most important economicresource-and virtually the only ones in countries like Kuwait, Qatar, orthe United Arab Emirates, whose economy is based almost entirely on oilextraction.

Extractive activity

Some extractive activities in deserts are very old; the saltworksin the Sahara, the Thar Desert, and other deserts are as old as thedevelopment of the caravan trade routes and, in some places, even older.The extraction of caliche or Chilean saltpeter (sodium nitrate) from thedesert areas of contemporary northern Chile dates back to pre-Colombiantimes. Whether ancient or modern, mineral extraction is exceptionallydestructive, especially opencast mining, which is increasingly common.Low local populations, ground that costs little or nothing, and thedifficulty of access for potential observers mean that mines in desertsare less likely to be well managed and monitored. On the other hand, thedifficult access and transport, together with the difficult workingconditions, mean that in most hot deserts it is only worth extractinghigh-value minerals, mainly precious stones, valuable metals, uraniumand other rare metals, and those that can be highly mechanized (such asdeposits of oil or natural gas).

Historically, precious metals were the first minerals to attractthe most daring and ambitious prospectors to some deserts: gold from theSahara (which, in fact, was not extracted from but only crossed theSahara in caravans) stimulated the medieval imagination and was one ofthe main motives spurring Portuguese explorers to follow the Africancoastline, where they gave the name Rio de Oro (River of Gold) to thecoastline of the western Sahara; in the Americas, silver attracted thefirst colonists to the Mexican and Chilean deserts; in Australia, goldwas found in 1892 in Coolgardie, a desert region about 311 mi (500 km)east of Perth, and attracted more than 100,000 men in four years. InDeath Valley (California), so much borax was extracted that, after 1880,columns of up to 20 mules pulled cart trains of it for more than 125 mi(200 km).

Petrol is now by far the most important mineral product extractedfrom deserts. The largest reserves (more than half the world'sknown reserves) are found around the Persian Gulf, mainly in SaudiArabia, though there are also large deposits in northern Africa(especially in Libya and Algeria). Oil (and natural gas) drives theeconomies of these countries and may be their only source of foreigncurrency. This source, however, is now highly productive and has madethe beneficiary countries among the richest countries in the world,causing deep changes in their societies. It has also given rise tocountless frontier conflicts, the most serious of which led to theIran-Iraq War (1980-1988), Iraq's invasion of Kuwait (1990) and theGulf War (1990-1991). Pollution, a major problem in the Gulf even beforethese wars, has worsened considerably in the last 15 years, especiallyduring the Gulf War and the following months, when the Iraqi army leftbehind more than 500 burning oil wells, a slick of 4-6 million barrelsof oil in the waters of the Gulf, and discharges of 150 million barrelson dry land. All of these seriously contaminated soil, vegetation, andaquifers.

The environmental impact of mining

The impact of large opencast mines is spectacular. When theexploitation is fully operational, immense craters are dug tens or evenhundreds of meters below the original ground level, and huge quantitiesof waste accumulate; though as much of the mineral has been removed asis profitable, enough remains to contaminate large areas of land and therelated aquifers, and it gives rise to dust with high levels of heavymetals. The large copper mines in the Atacama Desert and some in Nevada(United States)-among the largest in the world-are major sources ofdirect and indirect pollution.

Mining, by definition, is the exploitation of a nonrenewableresource in a given site until it is exhausted. Therefore, except inextraordinarily rich or large deposits, this activity is limited in timebut potentially generates great wealth. In the case of the deserts (andthe developing countries in general), though, this wealth does not havebeneficial effects on the local economy; rather, it accrues in thedistant financial centers that provided the original investment to makeefficient exploitation of the resource possible.

Thus, little of the wealth created by uranium mining in theRepublic of Niger or diamond mining on the coast of Namibia hasbenefited these countries, although the landscape has been destroyedwith toxic slag heaps and contaminated aquifers. Even in developedcountries, there is an unequal distribution of benefits and costs;because the mines are in relatively unpopulated areas, the companiesalways come from outside and employ more labor from outside than fromthe local labor pool, and they rarely reinvest in the same site, seekinga new site when the mine has been exhausted.

90 Camels (Camelus) have played a major role in human adaptation tothe desert. The camel was domesticated long ago--about 5,000 yearsago--and has since become vital for the nomadic populations of the OldWorld's deserts and subdeserts because of its many uses in thesehostile climates. The camel provides food, leather, and fuel (its dung)and is an excellent beast of burden and mount; it has long been used inwarfare and for other military purposes. The existence of camel marketssuch as the one in the photo in Pushkar (Rajasthan, India) is thereforequite basic, and the deals struck there are of great importance.

[Photo: DPA / Images of India]

91 The large lakes in the Sahara during the Quater-nary climaticoptimum, roughly 10,000-12,000 years ago, were a reflection of the highprevailing levels of humidity and had abundant flora and fauna. Theyhave all since disappeared, except for Lake Chad (limited to the mosttropical part of the region and now much smaller than in the past) and afew sebkhas or chotts. In fact, the Saharan region has been occupiedsince the early Pleistocene by a mosaic of deserts, subdeserts, and lessarid areas that have expanded and contracted with climatic fluctuations.The map only shows one of the wetter periods through which the regionhas passed. The names correspond to the areas that the lakes would nowoccupy, when identification is reasonably certain.

[Drawing: IDEM, based on Lay, 1991]

92 The construction materials and architecture used in desertvillages are often lessons in optimizing the use of natural resources.Ait Arbi, in the Valley of the Dades (Morocco) is one of the manyexamples of multipurpose design, adapting the architecture to the desertenvironment while making the most effective use of space. In thesouthern Atlas, where the population is mainly Berber, there are manyksars, fortified villages typical of the preSaharan zone in the valleysof rivers like the Dra, Dades, Gheria, and Ziz. In these traditionalconstructions made of stone, adobe, and mud, the dwellings are designedto occupy the maximum possible space by limiting the exposure of theexternal walls to the rays of the sun. The upper stories and internalcourtyards are also orientated so that they are protected from thelight, and the inhabitants move from room to room over the course of theday. During the daytime, the ground floor is coolest, but at nightinhabitants prefer to sleep on the flat terrace roofs, where during theday fruit and grains are dried in the sun. The materials used in theconstruction of the ksars are the best to achieve this balance betweenarchitecture and environment. The dry mud covering the external wallsheats up very slowly during the day and releases the accumulated heat atnight. The internal rooms stay at an agreeable temperature during theday thanks to their high roofs. This magnificent adaptation to theirenvironment has not, unfortunately, prevented many of these traditionalsettlements from suffering gradual population loss, as many of theirinhabitants prefer the comfort of modern buildings.

[Photo: Adolf de Sostoa]

93 The term blue men often applied to the Tuareg refers to thecolor of their clothes and above all to their veil, or litam, perhapstheir most typical item of clothing (see figure 104). This intense darkblue is obtained by dying clothing with indigo, a coloring agentobtained from several legumes of the genus Indigofera, mainly I.tinctoria, I. arrecta, and I. articulata. As the traditional dyingmethod is rudimentary, the color runs, often giving the wearers'skin the bluish color for which they are named. (Many Tuareg aremelanoderms, but those with lighter skin show the blue more clearly.)The photo shows Tuaregs riding through the streets of Djanet (Algeria)on their typically arrogant-looking camels. The Tuareg, whose weaponsinclude a sword and a dagger hanging from their arm, have always soughtto distinguish themselves from the other Saharan peoples, whom they haveoften subjected or at least attacked on their journeys through thedesert.

[Photo: Sandra Prato / Bruce Coleman Limited]

94 The Afar of the Danakil Desert in Ethiopia are strong, tall,thin and dark-skinned and accustomed to the harshest desert conditions.They are nomadic herders who herd goats and sheep, like the group shownin the photograph, and they also raise some camels. The Afar usually setup tents, which they take down to transport on their travels, makingtheir caravans look very unusual, with the long tent struts formingcurved bundles. Though their economy is based on stockraising, theysometimes trade with other tribes. Also known as Danakil after theregion where they live, the Afar are Muslim Cush*tes, but they stillmaintain many of their ancient animist traditions.

[Photo: Dieter & Mary Page / Survival Anglia / OxfordScientific Films]

95 The !Kung are San hunter-gatherers, like these two peoplephotographed in the Kalahari Desert. An African people with a culturewell-adapted since ancient times to the hostile desert environment inwhich they live, the !Kung used to live in the western and southernsavannahs of Africa, but since the early twentieth century they havebeen restricted to the Kalahari Desert in Botswana and Namibia. Onlyabout 5,000 of the remaining 50,000 San retain their traditionalhunter-gatherer lifestyle. The women and children go out to find plantsand small invertebrates, while the men are responsible for catchinganimals for extra protein in their diet.

[Photo: Anthony Bannister / NHPA]

96 The great civilizations of ancient Mesopotamia developed in thehot deserts of western Asia between the Tigris and the Euphrates. About12,000 years ago, hunter-gatherer groups in the area took up agricultureand turned part of this arid area into fertile oases that were laterenvied by nomadic groups such as Hurrians, Kassites and Guti. The mostimportant civilizations, the Sumerian, Babylonian, and Assyrian, were attheir height 5,500-2,600 years ago. Other peoples such as the Elamitesor the Semites had a huge influence on the development of thesecultures. The Sumerian civilization is the oldest of all knowncivilizations. It appeared 5,500-5,000 years ago, when several separatesettlements came together in walled cities. In 2340 b.c. the Sumerianswere conquered by the Akkadians arriving from the northwest. TheAkkadians assimilated many Sumerian features into their culture, amongthem the organization of their cities, their laws, and their monumentalarchitecture. Sumer and Akkadia were unified under Babylonian law andhad a highly organized administrative system. During the Babylonianperiod, commerce, art, and science flourished. Later, Babylonian culturespread under the Assyrian empire from the Persian Gulf to theMediterranean. The Urartians from the mountainous regions of Lake Vanwere for a long time the greatest enemies of the Assyrians, but much oftheir culture came from the Assyrians. The Assyrian empire collapsedabout 2,600 years ago due to the pressure of the peoples on theirnortheastern border.

[Drawing: IDEM, based on GEC]

97 On the edge of the Thar Desert, the medieval walled city ofJaisalmer (India) has many beautiful temples and a sophisticated ancientsystem used to extract water and store it in an area where water is veryscarce. Other cities in the area, like Jodhpur, also have similarsystems. The presence of wells, large deposits, and water distributionsystems that are in many cases architecturally stunning and highlybeautiful suggest that the desert peoples planned their use of waterresources very carefully. Unfortunately many of these large deposits(often situated within the city the walls, so the water could not bepoisoned by an enemy) have been converted into garbage dumps and are nolonger cleaned regularly. In the last few decades, due to irrigation andespecially excessive pumping of underground water, the TharDesert's already low water table has fallen alarmingly. This showsthat deposit systems are both cheaper and less damaging than modernpumping and channeling methods.

[Photo: Josep Pedrol]

98 This drawing shows the links between the Afro-Asiatic languagesproper (HamitoSemitic) and Omo-tic languages. Until recently, the Omoticlanguages were considered a subgroup of the Cush*tic languages, but mostlinguists now consider them a separate but closely related branch of theAfro-Asiatic languages. The Afro-Asiatic languages contain five mainfamilies: ancient Egyptian, Semitic, Berber, Cush*tic, and Chadic. It isdifficult to classify the languages in each of these five branches, andthe method proposed here is only one of many possibilities. There arewritten traces of ancient Egyptian more than 6,000 years old; this gaverise to Coptic, which is now used only in the liturgy of the Copticchurch. The Semitic group is perhaps the most widespread, including thewhole of northern Africa and reaching southwest Iran; it is also spokenin the areas where Islam has arrived. In addition to Arabic andHebrew--the best-known Semitic languages--the family also includesAramaic, some Ethiopic languages, and Ge'ez, now used only in theEthiopian church. There is written evidence of Aramaic dating from morethan 3,000 years ago. About 2,000 years ago, Aramaic was the dominantlanguage from Mesopotamia to Palestine, but it was later replaced byArabic. It is still spoken by some peoples in northern Syria, Iraq,Iran, and south of the former Soviet Union, though the number ofAramaic-speakers does not exceed 100,000. The diverse Berber dialectswere spoken in a continuous strip across northern Africa, butBerber-speakers are now divided into separate groups. The differentlanguages of the large Cush*te group, are scattered throughout Somalia,Ethiopia, Kenya, Tanzania, and Sudan, while the Chadic languages, thebest known of which is Hausa, are spoken in Chad, Nigeria, Cameroon, andthe central African Republic.

[Drawing: IDEM, based on Junyent, 1989]

99 Islam is present throughout the Old World's hot deserts, asis shown by their decorative arts and the most common expressions oftheir culture. This house of a Muslim in Luxor in the Valley of theKings (Egypt) is decorated with scenes from his pilgrimage to Mecca,telling the world he has performed the hajj. The details shown includethe sacred spaces, the means of transport, the environment, the animalsand plants, the prayers and the camel transporting the kiswah, and thesacred black brocade cloth that covers the Black Stone (the Al-Kabah orKaaba shrine), which in the past was woven in Egypt. The journey is inthe first 15 days of the month Dhu'l-Hijja, after Ramadan. Over aperiod of four days, several complex rituals must be performed whilewalking around the sacred space of the Kabah, the cubic temple said tohave been built by Abraham. For Muslims, it is the house of God onEarth. Every year Saudi Arabia receives about two and a half millionpilgrims from all over the world who come to fulfill one of the fiveprecepts of Islam. In the times of Muham-mad, Mecca was a stopping pointvisited by caravans from distant regions in search of water from itswell. Once a year, it became a center of trade and exchange.Muham-mad's religious discourses, attacking the huge proliferationof divinities and defending the existence of a single god, came intoconflict with the interests of the city's merchants. In 623 a.d.Muhammad and his followers had to abandon Mecca and take shelter inMedina. This journey, the Hegira, was the beginning of the century thatsaw Islam become a huge empire.

[Photo: Rosa Carvajal]

100 The personal nature of body decoration in Australian Aborigenesis shown by this man's work painting his skin to participate in theButterfly Dance in Arnhem Land. The Aborig-ines developed a very closerelationship with the materials of their surroundings; their highlycomplex totem culture was linked to the land and landscape. The ochrethey adorn themselves with also has a symbolic importance. Obtaining it,grinding it, and using it has become a ritual process, which sometimesforms part of ceremonial acts. The drawings depend on the occasion andon each individual's totemic rights. Good quality ochre used to begreatly appreciated and was a valuable item for barter between differenttribal groups.

[Photo: Jean-Paul Ferrero]

101 The decorated pottery of the Mimbres Indians, with a profusionof shapes and drawings, is one of the most representative elements ofthis former agricultural culture of the southwest United States. Theearliest designs are simple geometric forms decorating the outside ofglobular receptacles such as saucepans, cups, and jars. Descriptivemotifs appeared later, as seen in these black-and-white designs from abowl 2,900-3,500 years old, now in the Maxwell Museum at Taos (NewMexico). In the most southern area, the decoration also included animistrepresentations. The Mimbres Indians adopted pottery late, and for along time objects for personal use were made mainly of wickerwork (theorigin of the Castillian Spanish term mimbre) and were also decorated.

[Photo: John Cancalosi / Auscape International]

102 When the Spanish conquistadors reached the hot deserts of NorthAmerica, there were about 100,000 indigenous inhabitants divided amongabout 40 different peoples. They all lived in a similar aridenvironment, but each people had its own language and culture. TheRancheria Indians lived in small, scattered agricultural settlements,while the Pueblo Indians founded agricultural cities along the RioGrande and on the plateau drained by the Colorado River. Other peoplessuch as the Apache, Ute, and Comanche were nomadic hunter-gatherers. TheSpanish arrived around 1540 in search of the fabulous treasures rumoredto be in possession of the local peoples. They explored the entiresouthwest region of North America in search of gold but returnedempty-handed. Catholic missionaries followed them on the same route insearch of souls to convert. After the missionaries came the colonistswho built farms and cities; colonial authorities installed barracks andcourthouses. Several Indian tribes tried to resist the invaders, butthese uprisings were harshly repressed. In 1680 the Pueblo Indiansmanaged to expel the Spanish from the region of Santa Fe, but 13 yearslater the Spanish destroyed the city and executed 70 Indian chiefs inretaliation. The indige-nous population declined, while that of Spanishcolonists increased. About 20,000 people of Spanish descent lived in thearea by the late eighteenth century, when the Spanish empire began tocollapse in Europe and its overseas possessions became vulnerable.Mexico's independence in 1821 opened the way for theAnglo-Americans, and the Spanish definitively lost the arid areas ofNorth America.

[Drawing: IDEM, from several sources]

103 The extremely realistic pottery of the Mochica people, much ofwhich still survives, has made it possible to reconstruct the lifestyleof this agricultural and warrior people who settled the deserts betweenthe Andes and the Pacific Ocean. Each piece of pottery shows a person ora scene from Mochica daily life; the pot in the picture (2,800-2,200years old) represents a woman kneeling. The documentary importance ofMochica pottery is even greater because the pre-Columbian populations ofSouth America did not develop any system of writing; thus, the mainfeatures of their culture can only be reconstructed from archeologicalmaterial.

[Photo: Museo del Oro, Lima / Giraudon]

104 The clothing of desert dwellers is especially important inpreventing dehydration. The Tuareg in the photo are wearing clothes thatcover almost their entire bodies, protecting them from the desert sunand sand. Air can circulate in the space bet-ween the clothes and theskin, thus preventing excessive water loss through transpiration. Whenthey have to perform heavy physical exercise, they take off theoutermost layer of clothing so that they are cooled by the sweatevaporating from their skin. Their clothing is usually dark, becausedark colors provide better insulation and the dust of the desert is lessobvious than on light colors. Women in nomadic groups do not usuallywear a veil, but most men of the nomadic groups of Arabia and northernAfrica wear something to cover their head, especially the Tuareg men.The veil covering the man's face (see photo 93) protects it fromthe desert wind and from the evil spirits that live in dark lonelyplaces. The Tuaregs' blue clothing is the origin of the name bluemen, though the Tuareg call themselves kel tagilmust, which means thepeople of the veil.

[Photo: Charlie Nairn / The Hutchison Library]

105 The classic tents of desert nomads, such as the ones in thisBedouin camp in Jordan, consist of thick goat or camel leather raisedabove the ground on four posts. Sometimes this cover is of a materialfiner than cotton or of sewn goat skins (10-100 animals are needed tomake a single tent). Other tents similar to those of sedentary peoplesare built with blinds covering a wooden framework. Inside, the ground isalways covered with a carpet. Some tents are rectangular, while othersare circular or relatively elongated, and the largest are 33- 39 ft(10-12 m) wide.

[Photo: Tony Morrison / South American Pictures]

106 Kwashiorkor is a condition caused by an unbalanced diet thatmainly affects children between six months and three years of age. It isdue to a diet deficient in protein but rich in starches, which providesufficient calories. Bacterial and parasitic illnesses may aggravate theproblem. A protein deficiency might suggest that children affected bykwashiorkor would be very thin, but in fact they are rather distended,like this Somali boy. The deficiency takes many other forms, includingmajor behavioral disturbances and general listlessness. Attempts tosupply the protein needed through milk powder have been a waste of timeand money--in many regions of the Third World children who aremalnourished cannot tolerate lactose.

[Photo: Christine Osborne Pictures]

107 The collection of fruit and other succulent plant materialscontaining abundant water is of great importance for the San tribes ofthe Kalahari Desert, as in such a dry habitat the limiting factor is notfood intake but water intake. Wild squashes (Cucur-bitaceae), such asthis Gems-bok cucumber (Acanthosicyos naudinianus) about to be harvestedby a woman, are very important (see figure 55). Though the rain fallingin the Kalahari is not enough to maintain a minimum grass, shrub, oreven tree cover, permanent bodies of water are extremely scarce, and therains dry up quickly. For the San, it is thus essential to know therhythms of the seasons and to keep track of water sources, includingplants that can provide water.

[Photo: John Downer / Planet Earth Pictures]

108 The small desert trees known as incense trees (Boswelliacarteri, upper photo) and myrrh trees (Commiphora myrrha, lower photo)played, and still play, an important role in many religions. Theyproduce gum resins (incense and myrrh, respectively) burned to spreadtheir essential oils in the air and perfume their environment. Thereligious use of these two products began in funeral ceremonies todisguise the smell of the body and later acquired a purificatory,liturgical, and sacrificial meaning. As incense and myrrh were alsoclosely associated, the plants that produced them were also confused.Both belong to the family Burseraceae but are different from each other,as shown by these plates from the first volume of Medicinal plants by R.Bentley and H. Trimen, published in 1880. Myrrh and incense are stillused for similar purposes in the cosmetics industry, perfumery, and thepharmaceutical industry, and also as fumigants.

[Photos: Board of Trustees of the Royal Botanic Gardens, Kew]

109 Body decoration with henna (Lawsonia inermis) paste. Henna isone of the oldest known dyes for skin and hair. According to tradition,the prophet Muhammad (570-632) used it to dye his beard red, and it haslong been a popular natural dye. Women use it to color their cheeks,hands, and feet and paint their nails, and in India the custom is forthe bride's hands to be painted with complicated designs usinghenna. Berbers also use henna in marriage ceremonies because theybelieve it has seductive properties. For the Berbers, henna has a mysticand religious significance as well, and they feel it strengthens thelink between mankind and nature. The coloring agent is a symbol ofyouth; they paint their entire bodies with it.

[Photo: The Hutchinson Library]

110 The manipulation of sisal fibers in a Mexican workshop. Sisalfibers are extracted from the leaves of Agave, dried, and used to makerope. Several species of Agave, all of them from the arid and semiaridregions of the Western Hemisphere, produce good fibers. One of the mostimportant is sisal (A. sisalana), originally from Mexico, the name ofwhich is taken from the port of Sisal in Yucatan, the first port toexport the fiber in the nineteenth century. It is now mainly cultivatedin Brazil (annual production is about 20,000 tons) and in some countriesin eastern Africa such as Kenya, Tanzania, and Madagascar. Sisalcultivation and processing the fiber require a great deal of labor and alot of water. The leaves are cut, their tips are removed by hand andthen mechanically washed (consuming 38,041-47,551 qt [36,000-45,000 l]of water per hour), meaning the future does not look very good for thesisal industry.

[Photo: Edward Parker / Still Pictures]

111 The woody structure of some columnar cacti is a good source ofwood for building purposes. These include the saguaro Carnegieagigantea, upper photo, which has large cylindrical rods running frombottom to top (see also photo 39). This is very different from theprickly pear Opuntia fulgida (see middle photo), whose woody structureis reticulate. The best trunks are those of the pasacana (Tri-chocereuspasacana), used as planks for all sorts of purposes, including this doorto the bell tower in Tocanao in the Atacama (Chile).

[Photos: Ramon Folch / ERF]

112 Changes in the area of esparto grass in northern Africa and theesparto plant biomass in the arid areas of Algeria under a grazingregime. The industrial use of the leaves of esparto grass (Stipatenacissima) to make high-quality paper has led to overexploitation ofthe areas of esparto grass in northern Africa (upper diagram). In lessthan 100 years, the area occupied by esparto grass has declined by 62.5%and is still declining at a rate of 1.2% per year. The biomass of thisplant has decreased, as shown by the changes in the biomass of espartograss in Algeria from 1976-1986 (lower graph). Esparto production hasbeen seriously affected. In the early twentieth century, annual tradewas almost one million tons a year. This declined to 400,000 tons by the1950s and to about 100,000 tons in 1995. Therefore, the esparto tradehas declined by about 90% in this century.

[Drawing: IDEM, from data provided by the author]

113 Goats browsing in the treetops are a typical image of tropicalarid and semiarid grazing areas, shown by the goats in the photo takenin southwest Morocco. (They have clim-bed up an argan [Argania spinosa,Sapo-taceae].) In desert zones, the vegetation is so poor thatherbivores are forced to browse on woody plants. Their great ability tobrowse has made goats one of the main causes of the spread of deserts inNorth Africa and Asia. One remedy might be to replace them with camels,which would be mo-re productive and would allow for more rational use ofgrazing.

[Photo: Daniel Heuclin / NHPA]

114 The number of stems of woody plants is inversely proportionalto the diameter of their crowns, as shown by this graph of thegrasslands in the Sahel in Africa. The greater the density of trees andshrubs, the less space they have, so that the percentage plant covercorresponding to each tree is also lower. Note that in arid regions, theappearance of each plant and of the woody cover in general is not onlydetermined by the area's microclimate but also by the intensity ofgrazing and the livestock's type of food. Large herds of browsinganimals such as goats and camels can considerably reduce the woody coverby eliminating all the young shoots. If browsing is intense andcontinuous, it can lead to desertification in the long term.

[Drawing: IDEM, from data provided by the author]

115 The grassy scrubland of southern Africa that forms on sandysubstrates contains other plants as well as grasses. This photo of theKaroo shows a flowering specimen of Hoodia bainii, (Asclepiadaceae), aperennial plant whose succulent stems are protected by rows of spines.The spines are very useful, protecting it from herbivores and reducingwater loss due to evaporation by creating a thick layer of air saturatedwith water vapor next to the plant's surface. Spines also reflectand disperse the sun's rays. This plant stores its seeds, which arelike parachutes, within pods that only explode and release the seedsunder certain conditions. Once released, the seeds are dispersed by thewind.

[Photo: Peter Steyn / Ardea London]

116 The mulga (Acacia aneura) has very diverse applications. Thisspecies, represented here by a specimen in western Australia, is plantedto stabilize soils and as an ornamental; it also provides timber,firewood, fodder, and food. The timber, with a narrow light band ofsoftwood and a darker heartwood, is celebrated for being tough, heavy,and resistant. It is used for carvings, to make fencing and props, andas a fuel. The large succulent galls, known as mulga apples, are a goodway to quench thirst, and the pods contain small seeds with a highprotein content (23.3%), which are consumed in large quantities. Theseseeds could be used to make bread, and the food industry could surelyfind some use for the proteins from the seeds. Other mulga productsconsumed by Australian Aborig-ines include its gum and lerp, a sweetsubstance secreted by the honey ant (Austrotat-achardia acaciae). Thesmoke of burning mulga leaves is also used as a therapy after childbirthor to induce sweating in the sick.

[Photo: Jan Taylor / Bruce Coleman Limited]

117 The system known as qanat, falaj, or foggara--an ancient systemfor obtaining water and channeling it--is still widely used in thedesert regions of the Old World. The engineering and final purpose arealmost identical in the karez in the Turpan Basin, Xinjiang (China; seephoto 229). The system consists of a series of underground galleriessloping gently onward and bringing water from the mountain slopes to thevalleys, where springs are scarce or excessively salty. The engineeringis simple: a few vertical wells are drilled down to the water table, andfrom there a tunnel with a slight slope that goes down to the plain isexcavated. Along the route of these galleries, every 33-66 ft (10-50 m),are other vertical wells that give access to the water in the qanat,ventilate it, and make cleaning and maintenance easier. Its crater-likeform is due to the piling of the earth removed when the well is dug; theshape protects the opening from the solid objects that might fall in.The system of underground aqueducts reaches the surface near thecultivated fields, and the water is divided and flows along irrigationchannels to a large area. Qanat are usually a few hundred meters long,but some are several kilometers long. The system of channels does notrequire pumping and reduces losses by evaporation. Qanat are cheap andsafe, and they are widespread in Iran (which has 200 active ones), butthere are also many in other arid areas from western China to theMaghreb. The Spanish introduced them to South America, and in theAtacama Desert (Chile) there are about 15 (known as socavones) that arestill in use and collect water from the foothills of the Andes.

[Drawing: Jordi Ballonga, bas-ed on several sources]

118 Most oases have been turned into irrigated vegetable gardens,with a very wide range of herbaceous crops. This oasis is in Tinerhir inthe High Atlas (Morocco). It is dominated by palms, which are put tomany uses. Palms provide protection from the heat of the sun and thedesert winds. Some fruit trees can be planted under palms, among themfigs (Ficus carica), pomegranates (Punica granatum), apricots (Prunusarmeniaca), peaches (P. persica), oranges (Citrus sinensis), and lemons(C. limon). The ground left free under these trees is used to growvegetables. Palms have many other uses. Date palms (Phoenix dactylifera)not only provide dates but also material for construction and for makingfurniture; the leaves yield fibers to make rope and twine and the juiceof the shoots is used to make a sweet, milky, alcoholic drink.

[Photo: Cyril Ruos / Bios / Still Pictures]

119 There are many different varieties of dates on the market. Themost appreciated is the degla date, which is grown, for example, in theTaghit Oasis in the Great Western Erg (Algeria). This variety isexported and is an important source of wealth. The degla palm requireswater that is not very salty, but other varieties, such as thoseproducing ghar dates, grow where the water is salty. Ghar dates arestored in baskets as a long-term food reserve, but they are notexported. Dates are an essential component of the diet of oasisdwellers, as this nutritious fruit meets many of the body's foodrequirements, and date palms produce large amounts of dates. A date palmcan grow to a height of 98 ft (30 m) and live for 200 years. It reachesmaturity at an age of about 15 years and then produces about 198 lb (90kg) of dates a year.

[Photo: Josep Pedrol]

120 The seeds of the jojoba (Simmondsia chinensis, Simmondsiaceae)yield a liquid wax that is used to make shampoo and soap, lubricants formachinery, and many other uses. Jojoba oil is similar to sperm oil andmay well replace it, which would help whale conservation. It is alsothought that jojoba oil could replace most of the fuels derived frompetroleum. Jojoba is now cultivated commercially in large areas ofdeserts, since it can grow with very little irrigation water. These arenot, however, the only uses of jojoba seeds. The Indians of the SonoranDesert have long used them for medicinal purposes, and in Mexico theyare used as a good substitute for coffee.

[Photo: P. Morris / Ardea London]

121 Falconry is still very important in Arab culture, and falconmarkets, such as this one in Riyadh (Saudi Arabia). The Bedouin of theSahara Desert and the Moroccan kaid (high officials) use these birds ofprey to catch hares and thus take great care of their peregrine falcons(Falco peregrinus). They are kept in the owner's house or within atent, their heads covered by black hoods, and they are caressed and fedby hand. When the hunter sets out on horseback, the falcon is borne onhis shoulder or turban with its hood still on. As many as 30 riders mayhunt together, each with his own bird. When they see the prey, thefalcon's hood is removed and it is freed to hunt the prey. Thefalcon's hunting abilities are extraordinary. Its eyesight isincredibly good, and these daring birds can fly very fast and forrelatively long periods. They can kill creatures almost as large asthemselves, swooping down on their prey at speeds of up to 155 mph (250km/h); most prey die immediately in their talons before having a chanceto react.

[Photo: Erik Bjurstrom / Bruce Coleman Limited]

122 The fishermen of the inland delta of the Niger River usedifferent types of net, depending on the time of year and thecharacteristics of the waters they are fishing. Traps consist of aframework of branches, varying greatly in size and shape, covered by anet of nylon or some other material. The ones in this photo of a stretchof bank in Mali are known as durankoro and were introduced in the 1980s.Durankoro are traps that are left in position all year-round in singlefile, perpendicular to the flow of the current, in shallow water(usually in channels and on river arms). Normally, the women areresponsible for setting them up.

[Photo: Chris Dodwell / The Hutchison Library]

123 The Somali ass (Equus asinus somalicus) is one of the twosubspecies of wild African asses still found in scattered areas insouthern Sudan, Ethiopia, and Somalia. The original habitat of thisanimal was the rough stony desertland of northern Africa, but once itwas domesticated, the Somali ass was introduced into many of theworld's other hot biomes. Asses are surefooted, with strong hoovesthat are well adapted to rocky terrain. They are able to resistdehydration and have been a great help to the inhabitants of aridregions. An ass can carry a load of hundreds of kilos for several dayswith very little food, and can work in asphyxiating heat. In aridregions, only camels are better than asses as beasts of burden andmounts.

[Photo: Jean-Paul Ferrero / Auscape International]

124 The increase in the number of Tropical Live-stock Units and thearea under cereals matches the growth of the human population in thecountries of the Sahel between 19501990 (and shows estimates for theyear 2000 based on different hypothesis proposed in the 1990s). Thecensuses used to draw up this graph were from Burkina Faso, Chad, Mali,Mauritania, Niger, Senegal, and Sudan. The increasing growth oflivestock in the Sahel since 1950 has been the result of, among otherthings, a reduction in livestock mortality by a veterinary program thateliminated many diseases. In 1961 and 1962, laws were passed to preventfarmers from occupying grazing land. The increase in the number of headof cattle is not inconsistent with an increase in dry farming, as thecereals are grown for use in animal feeds. During the droughts in theSahel since 1968, the fodder available for the herds was greatly reducedand many animals died. The survivors concentrated around the wells,where they exerted excessive pressure on the scarce productive grazing.Yet these droughts did not have much effect on the long-term trendtoward the increasing number of livestock.

[Drawing: IDEM, based on data provided by the author]

125 The number of sheep in Algeria over the last hundred years hasbeen irregular. Until the 1920s, despite the large fluctuations, therewas an average of seven or eight million head of sheep; that decreasedto about five million between 1920-1970. In the 1970s, changes infeeding sheep, together with a vaccination program, caused a steepincrease; by the mid-1980s, there were about 10 million sheep.

[Drawing: IDEM, based on data provided by the author]

126 Sedentary stockraising is the main activity of the Hazara tribeof the central plateau of Afghanistan. The region they occupy is rich innatural grazing, and there is no shortage of places with water for theanimals to drink; as a result, their land has always been coveted byother Afghan peoples, and there are still rivalries between them. TheHazara are of Mongol origin and, according to tradition, are directdescendants of Genghis Khan (1167-1227). They zealously defended theirpastures, and for a long time no nomadic herders dared to enter theirterritories. By the late nineteenth century, the Hazara were dominatedby the terrible ruler 'Abd ar-Rahman, and during his time in powertheir livestock economy was impoverished. They still follow theirtraditional lifestyle, and their herds of goats can often be seengrazing below their villages, as in this valley of the southeasternHindu Kush.

[Photo: Richard Waller / Ardea London]

127 Raising sheep is the main stockraising activity in the drierareas of southern Africa. The first farms in this area were almostself-sufficient, and the shepherds bartered livestock for the productsthey needed. During the nineteenth century, the industrial revolutionled to increased demand for animal products, especially wool, and theformer subsistence stockraising spread to meet demand from foreignmarkets. Demand for wool increased greatly after 1830, and in the next20 years exports of this raw material increased two hundred-fold. Duringthis period the number of sheep increased fourfold. The arid pastureshad to support greatly increased grazing pressure, which led to majordegradation and soil erosion. Despite this, stockraising is stillconsidered a good way to make a living, and large herds--such as thesekarakul sheep in the southwestern Kalahari in Botswana--can still beseen searching for grazing.

[Photo: Anthony Bannister / NHPA]

128 Riyadh, the capital of Saudi Arabia, is in the Hanifah wadi, inan area where several drainage systems meet. This geographical locationhas made it possible to build this modern city in the middle of thedesert. West of Riyadh, there is a highly eroded sandy plain, and thereare similar outcrops to the east. To the northeast is the railwayjoining the city with Damman, the center of the oil industry. The growthof the oil industry has boosted rapid improvements in transportthroughout the country's eastern province, where there arecommunication links to Kuwait, Qatar, and the United Arab Emirates.

[Photo: Bernard Gerard / The Hutchison Library]

129 Motor rallies through the desert, such as the Paris-DakarRally, the Rally of the Pharaohs, and other smaller ones, areincreasingly common, and though they are localized they have a greatenvironmental impact. The problem with this and other leisure-relatedactivities lies in the visitors' lack of respect for the desertenvironment, which they often consider to be empty, ano-man's-land, and thus not deserving special care. The risk ofpollution in the rest areas is particularly high, especially whenseveral hundred people gather to watch the end of a race. Because therest sites are at the water points, there are only a few and they arealways the same on all the different routes. These competitions have aneven greater social impact, due to scandalous waste of fuel and moneyconcentrated for a few days in an area of extreme poverty.

[Photo: Denize-Francolon / Gamma]

130 The cities and housing developments that have grown up in thedeserts of the United States, like this one in the Coachella Valley insouthern California, have caused major environmental disturbances.Bringing water to these centers of population is expensive; it has to beextracted from aquifers, which then become exhausted, or from theneighboring agricultural areas. The water reserves needed for thefarmers' crops are then used to irrigate luxurious green spaces. Inthe complex United States economy, many different types of settlementshave grown up in the desert, ranging from industrial and agriculturalcities (Phoenix, Arizona) to large sports or recreational centers (LasVegas, Nevada) to residential developments for retired people.

[Photo: Stephen Krasermann / NHPA]

131 Small urban vegetable gardens around a well in Tombouktou(Mali), on the edge of the Sahara. The gardens are watered by hand withwater that is hauled up the stairs. Humans have not always respected theworld's arid and semiarid zones and have often degraded them so farthey cannot be recovered. Yet when people manage water supplies well,they can make these areas much more productive than would be expected onthe basis of the climatic conditions. Unfortunately, use of surface orunderground water in the desert has often been irrational, and in thelong term this has made the land cultivated even more unproductive.

[Photo: Timothy Beddow / The Hutchison Library]

132 The retreating isohyets and decrease of the flooded areas ofthe inland delta of the Niger. These floodable areas are of greatbiological richness and have been retreating little by little since thelate 1950s, especially after the major drought that began in 1969(clearly shown on the map by the difference between the isohyets beforeand after 1969). During the same period, the population increasenecessitated an increase in cultivated ground and a reduction in fallowperiods, which caused the soil's production to decline greatly andencouraged desertification. In order to preserve natural resources, lawspassed in the early 1960s banned agriculture where average annualrainfall was less than 16 in (400 mm; the 400 mm isohyet). The areasnorth of this line were intended to be used for stockraising, which wasto be thoroughly regulated. These laws, however, were never enforced,and crops spread as far as the areas with annual average rainfall below8 in (200 mm). In the central delta of the Niger, like many other aridareas, the climate normally shows large variations in rainfall, so goodlong-term planning is the only way to deal with these changes withoutgreatly diminishing the land's productivity.

[Drawing: Jordi Corbera, bas-ed on Quensiere, 1994]

133 The flow regime of many of the large rivers that cross desertshas been greatly altered by human activities since the mid-twentiethcentury. The construction of large dams and reservoirs, such as the manyregulating the variable waters of the Nile (upper diagram), has madecrop irrigation possible, while providing water supplies to the largecities. Huge amounts of hydroelectric power are also generated, butthere is a great reduction in the amount of water in the lower stretchesof the river. The Colorado River in the United States is another veryclear example, as its flow has declined drastically since the beginningof the twentieth century (lower left diagram). The low flow from1935-1939 was due to the construction of the Hoover Dam in 1935. Thisreduction became especially severe after 1960, and since then almostevery drop in the Colorado has been used, so that very little reachesthe river's mouth. In 1979-1980, exceptional flooding in the lowerstretches caused the volume of flow to increase, but floods like thisare very uncommon. Logically, the quantity of sediment in suspensionborne by the river has declined proportionately with the decline in thevolume of flow (lower right diagram). These sediments are of greatimportance for the cycling of nutrients and biological productivity inthe estuary ecosystem. Before 1930, the Colorado carried about 125-150million tons of suspended sediments a year to its delta in the Gulf ofCalifornia. When the Hoover Dam was completed, the sediment inputdeclined to 100,000 tons per year. Something similar is happening to theNile, which used to bear 100 million tons a year of sediment to theMediterranean, now reduced to 30 million tons.

[Drawing: Jordi Corbera, bas-ed on several sources]

134 Experimental crops in the middle of the Sahara Desert, inKufrah (Libya), where irrigation allows cereals and alfalfa (Medicagosativa) to be cultivated. The climate is favorable to plant growth allyear-round, and these fields may produce 14 harvests of alfalfa a year.Irrigation functions even with salty water; the soil has to be suitable,the drainage system adequate, and excess water has to be used to washaway the saline deposits. This project is not very cost effective,though. The water has to be pumped from very deep deposits and at greatexpense from fossil aquifers; eventually they will be exhausted becausethey are not replenished with new water. In the late 1980s, theseprojects seeking to transform the desert sands into croplands werecomplemented with other more effective projects.

[Photo: Derek Bayes / Aspect Picture Library]

135 The construction of artificial drinking troughs for livestockreduces pressure on former water holes. This means more animals can beraised. These new drinking points are normally constructed by diggingwells and hafirs, artificial lakes to store rainwater. Around each waterpoint, herds of goats, sheep, and camels anxiously await their turn todrink, as shown by the herds in the picture, taken in Kordofan, southernSudan. But as there is more water, the number of animals can increaseconsiderably, and the resulting overgrazing contributes to erosion andthe spread of deserts. If there are too many animals, complications willarise when the rains become scarce: grazing will be insufficient andmany animals may die. In such cases, grazing, not water, limits thenumber of head of livestock.

[Photo: Mark Edwards / Still Pictures]

136 The immense areas of salt in the Danakil Desert, at the bottomof the basin of the Ethiopian subsidence (see also figure 36), have beenmined since prehistoric times. These open-air mines produce about 20,000tons of salt a year. The mining techniques are sometimes very simple andhave little environmental impact. Some-times, however, large-scale saltextraction has great environmental impact. The salt mined in Danakil istransported to the mountain areas of Ethiopia in very long caravans ofcamels, mules, and asses of up to 20,000 animals.

[Photo: Mary Plage / Bruce Coleman Limited]

137 Oil wells have only been present in deserts for a short time,but their future may be equally short. By the middle of the twenty-firstcentury, most of the oil reserves of the world's desert regionswill be exhausted. Only the oil fields in Saudi Arabia, Iran, Iraq, andKuwait have a long-term future. The industry's short history is instark contrast to its huge ecological impact. The oil industry hascontributed to the development of very poor regions, replacing smallvillages of herders and hunter-gatherers with fast-growing modern citiesthat have filled the deserts with garbage. The Gulf War (1990-1991) andother disasters have often led to the release of huge quantities of oilon land or sea that polluted large areas. For many years natural gas, aby-product of oil extraction, was simply burned, as in the Bu Hasa oilfield (Abu Dhabi, United Arab Emirates) shown in the photo, whichgenerates large amounts of air pollution.

[Photo: Jacques Burlot / Gamma]