Previous, present, and future climate regimes structure desert ecosystems in a way that requires a physical and behavioral adaptation to the patch dynamics of primary production, water, and nutrient cycling in space and time. During pulses of bounty, the fragile seedlings of desert plants can germinate, establish, and prepare for long droughts, burying their roots deep into the desert soils and, to a large extent, it is this heterogeneity of pulses that drives the high biodiversity of desert ecosystems. Many organisms in the deserts already are near their tolerance limits. Desert biodiversity is likely to be vulnerable to climate change, especially in biodiversity "hotspots," such as in the succulent Karoo biome of South Africa, where 2,800 plant species face potential extinction as bioclimatically suitable habitat is reduced by 80 percent with a global warming of 2.7-4.9 degrees F (1.5-2.7 degrees C).
Deserts support about 10 people per sq. km. Humans in deserts undergo considerable dehydration, and therefore, have to cope with the dry environment for their survival with a panoply of behavioral, cultural, and technological adaptations. Traditionally, desert-dwellers were of three types: hunter-gatherers, pasto-ralists, and farmers, whose livelihoods are adapted to the spatial and temporal patchiness of their environment. The movements of pastoralists, for instance, mimic the variability and unpredictability of the landscape and range reserves. Desert agriculture occurs mostly around oases and desert rivers, which often provide silt and nutrients through flooding cycles.
Finally, the specific aesthetic features and atmospheres of deserts, their silence, wideness, beauty, bare-
ness, and emptiness has always created an intimate, spiritual relationship between humans and the desert landscape, leading to the creation of all three monotheistic religions in desert regions. They still remain places of spiritual inspiration and meditation today.
SEE ALSO: Agriculture; Deforestation; Desertification; Rain; Rainfall Patterns.
BIBLIOGRAPHY. A. Monem Balba, Management of Problem Soils in Arid Ecosystems (CRC Press, 1995); S.W. Breckle, Sustainable Land Use in Deserts (Springer, 2001); IPCC 2007, CLIMATE Change 2007—The Physical Science Basis. Contributions of Working Group I to the Fourth Assessment Report of the IPCC, www.ipcc.ch (cited November 2007); D. Jasper, The Sacred Desert: Religion, Literature, Art, and Culture (Oxford, 2004); Maryam Niamir-Fuller, ed., Man aging Mobility in African Rangelands. The Legitimization of Transhumance (Intermediate Technology Publications Ltd., 1999); J. Skuijns, Semiarid Lands and Deserts: Soil Resource and Reclamation (Marcel Dekker, 1991); United Nations Environment Programme, www.unep.org (cited November 2007); Walter Whitford, Ecology of Desert Systems (Elsevier, 2002).
Ingrid Hartmann Independent Scholar
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