A sizeable share of minerals and fossil energy used globally is exported from deserts Given their low productivity and harsh climate, deserts are only expected to support a relatively small human population. Yet, the conditions of deserts make them rich in a few non-renewable mineral resources, in quantities much larger than are required to satisfy the local population. These resources are often exported to nondesert regions. Water-soluble salts, which readily accumulate in desert deposits due to the ambient dryness, such as gypsum, borates, table salt, and sodium and potassium nitrates, have been historically a product of deserts (Walker 1997). Before the widespread use of industrially-fixed atmospheric nitrogen, nitrates used as fertilizers and explosives were mainly obtained from the Atacama Desert, whose saltpetre and salt beds also contain 40 per cent of the world's reserves of lithium, used in medicine and technology (Crawford 1990).

Several minerals, highly significant in the global economy, are mined in deserts, where they occur not because of current aridity but rather due to geological history. While the low vegetation cover in deserts may have facilitated mineral deposit discovery, heat and the lack of infrastructure make mining and transportation difficult. Thirty-eight percent of the global supply of bauxite (an aluminium source) is mined in Australian drylands (Venkatesh 2003). Fifty-two percent of the world's copper extraction in 2004 was mined from deserts in Chile, Australia and Mexico; 33 per cent of the world's diamonds were extracted in the drylands of Botswana and Namibia; and the deserts of South Africa, northwest China, Australia, Uzbekistan, and Mali accounted for at least 35 per cent of the world's production of gold. Twenty percent of global iron ore production and 35 per cent of its exports came from Australia, where many mines are located in the desert. Phosphate rock is mined in the deserts of Morocco (16 per cent of world production), Senegal (9%), Tunisia (6%), Jordan (5%), Australia (4%), and Israel (3%), adding up to 43 per cent of global production. Finally, half the world's uranium ores are mined in deserts (Kazakhstan, Niger, Namibia, Uzbekistan, South Africa; BGS 2006). The most important contribution of deserts to mineral wealth is their deposits of evaporite minerals - soda, boron, and nitrates (e.g. Chile saltpetre), which are not found in other ecosystems.

More than for their mineral exports, deserts are renowned for the provision of biologically-derived but non-renewable energy resources, which dramatically boost the political standing and the per capita GDP of several desert countries. Thus, deserts contribute slightly above 50 per cent of world oil production and contain 75 per cent of i ts reserves, while 28 per cent of the world's natural gas reserves are found in the West Asia, North Africa and Central Asia (IEA 2005).

Deserts also export biological products to the rest of the world

Renewable resources - agricultural and other biological products - are also exported from deserts to non-desert areas. This may sound surprising, since usually the low biological productivity of deserts hardly even provides for the needs of desert inhabitants. Yet, some desert countries, such as Turkmenistan and Uzbekistan, practice irrigation agriculture and export much of their produce, like cotton. Also, due to the mild winter temperatures of many deserts, it pays to invest in water resource development for the intensive production of vegetables, fruits and cut flowers, which fetch high prices when exported to non-desert areas, where and when temperatures are significantly lower and inappropriate for the production of these crops. Thus, dates, vegetables and cut flowers cultivated in the Negev Desert of Israel are exported to Israel's non-desert markets serving 90 per cent of its population, and part of this production is also exported to European markets.

Another type of non-conventional desert export is derived from aquaculture practiced in Arizona and Israel. This includes crustaceans and fish that, when raised in closed systems that reduce evaporation, are paradoxically more efficient in water use than desert plants, and cheaper to cultivate due to mild winter temperatures and the low cost of land. Also, biologically-derived valuable chemicals, produced by micro-algae, are manufactured in deserts by capitalizing on their year-round high solar radiation, and exported to global markets (see Box 5.5).

Many countries with large deserts, such as China and India, export herbal and medicinal plants (Koocheki and Nadjafi 2003). Germany, for example, imports some 1 500 plant species for medicinal purposes, fewer than 100 of which are cultivated on a large scale, while the others are collected from the wild (Plant Talk On-Line 1997). Since deserts harbour large numbers of medicinal and herbal plants traditionally used by desert and non-desert people - for example, 95 per cent of disease treatments of the Thar Desert are provided through the use of 85 desert plant species (Ahmad and others 2004) - it is likely that in this export desert plants play a significant role.

Deserts hold a potential for bioprospecting

Besides exporting wild or cultivated herbal and medicinal plants from deserts to non-deserts, desert plants can be expected to catalyse the global pharmaceutical industry. The assertion that desert flora can be bioprospected for chemicals derived or extracted for medicinal use is rooted in findings that many evolved adaptations to the stressful desert conditions are chemically-based, such as compounds of anti-oxidative or of antiherbivory action extracted from desert plants. Indeed, recent screening of plants in the Negev Desert led to the identification of a few species with cytotoxic and antimalarial activities (Golan- Goldhirsh and others 2000), and some plant species from deserts in Argentina and Arizona and arid regions in Morocco have demonstrated activity against human diseases (for example, uterine cancer and infectious microbes), while their activity against a non-cancerous cell line was much lower, thereby indicating that disease-specificity may be prevalent (Donaldson and Cates 2004). It was also found that essential oils from two plants of Morocco's deserts, active against certain cancer cell lines and microbes, enhance poultry growth, reduce mortality, and increase the efficiency of feed conversion. They can be therefore used to replace antibiotics in poultry feeds, thereby reducing the evolution of antibiotic resistance (Donaldson and others 2005).

Yet, none of the known active compounds of desert plants have yet worked up to the level of a certified pharmaceutical in worldwide clinical use, though there are several patented claims for medicinal properties of such compounds, and a dryland plantderived dietary supplement (the Kalahari Desert Hoodia gordonii, alleged to control appetite) is commercially marketed. Thus, the pharmaceutical potential of desert plants has yet to be tapped.