Endangered Species Handbook

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Grasslands, Shrublands, Deserts

Destruction of Drylands

     Humans began adversely affecting natural grasslands some 50,000 years ago with the introduction of livestock.  Herders set fires to grassland to maintain it for grazing, but frequent fires caused deterioration of these ecosystems and eliminated many native species of wildlife that could not adapt.   To protect their livestock, herders killed off competing wild ungulates and persecuted predators and rodents, contributing to the decline of natural grassland ecosystems.
     As livestock gradually replaced wild ungulates, grasslands around the world turned to shrub and desert.  Millions of cattle, sheep, goats, domestic camels and yaks have come to dominate the ecology of grasslands wherever they exist, often eliminating native species of wild perennial grasses that anchored the soil with their extensive root systems.  In their place, annual plants and exotic species of grasses now dominate many grassland environments.  Domestic goats may be the worst offenders; they pull grass out by the roots, damage shrubs and trees by stripping them of all vegetation and climb low trees to graze.  Once the vegetation has been stripped and the roots are removed, wind blows the topsoil away or rain carries it off.
     When livestock is removed, grasslands may be able to recover if the damage is not too severe.  But plowing, especially by modern deep plows, obliterates all vegetation, including dormant seeds, and wildlife.      Natural grassland and shrubland are fast disappearing under the plow, endangering a growing number of plants and animals.   Chemical fertilizers do not nourish the soil as well as natural invertebrates, decayed vegetation and animal dung.  Unlike the soil in natural grasslands, chemically fertilized soil easily becomes hard and impermeable. The result is less productive soil that requires the use of more and more synthetic fertilizers each year to produce the same size crop.  Because artificial fertilizers do not contain natural micronutrients, crops grown using them may be nutritionally deficient.  Moreover, fertilizer nitrates that enter the water have produced algal growths in rivers and coastal regions that are so dense they choke out all forms of life, leaving "dead zones." 
     Many agricultural crops, especially those grown in arid regions, require artificial irrigation.  Sources include underground reservoirs, fed by rainwater that fell thousands of years ago, that underlie many deserts and shrublands.  Known as fossil aquifers, they have recently been exploited through deep wells and are rapidly becoming depleted in portions of the Sahara, Namibia, Saudi Arabia and the United States.  The aquifer beneath the Great Sand Desert of Iran has been pumped out, leaving only a low flow of brackish water (Allan and Warren 1993).  In Saudi Arabia, aquifers are being depleted by water used in wasteful forms of irrigation that cause salinization of the soil.  Heavy applications of water bring natural salts in the soils to the surface, resulting in a surface soil covered with salt crystals that renders the soil sterile unless the crystals are removed (Allan and Warren 1993).  Salinization is destroying land in many parts of the world, affecting more than 30 percent of all irrigated deserts (Allan and Warren 1993). 
     Grassland and dryland areas are among the most threatened of all habitats, according to an appraisal of ecosystems and centers of biodiversity that has designated 200 ecoregions in the world (Grove 1999).  These include temperate grasslands and Mediterranean-type shrublands, which are also rich in diversity (Grove 1999, Mittermeier et al. 1999).  Conservation plans for preserving many of these areas become ever more important as they disappear or are degraded.
     The misuse and overuse of grasslands has already turned millions of square miles into shrub and desert.  With the rise in human populations around the world, the process is accelerating. Each year, an area the size of Texas turns to desert.  The spread of deserts is threatening the livelihood of the 650 million people who live in these arid regions (Ponting 1991). The global warming climatic pattern may be accelerating this process.  Studies in the early 1990s by the United Nations Environment Programme (UNEP) estimated an area equal to North and South America combined ‒ about 8 billion acres of grassland and cropland ‒ was in danger of desertification worldwide
(Pitt 1993).  Since then, the problem has worsened.  An estimated 75 percent of Africa is already considered degraded (Simons 1994).  Desertification has claimed 39 percent of the 76 million hectares (188 million acres) of once productive grassland in Mediterranean Europe and 82 percent of the 142 million hectares (351 million acres) of Western Asia's productive steppe land (Goriup 1988).
     UNEP reported in 1986 that rangelands are turning to desert at an increasing rate:  85 percent of rangelands in North Africa, 30 percent in Mediterranean Europe and 85 percent in Western Asia (Goriup 1988).  Some studies have projected that should present trends continue, within 30 to 40 years, over half of the African continent, much of Central Asia, the majority of southern and eastern South America, most of central and western North America and about 90 percent of Australia will become desert (Allan and Warren 1993).

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