Deserts and xeric shrublands are abiome defined by theWorld Wide Fund for Nature.[1]Deserts and xeric (Ancient Greekξηρόςxērós 'dry')shrublands form the largest terrestrial biome, covering 19% ofEarth's land surface area.[2] Ecoregions in this habitat type vary greatly in the amount of annual rainfall they receive, usually less than 250 millimetres (10 in) annually except in the margins. Generally evaporation exceeds rainfall in these ecoregions. Temperature variability is also diverse in these lands. Many deserts, such as theSahara, are hot year-round, but others, such as East Asia'sGobi Desert, become quite cold during the winter.[1]
Temperature extremes are a characteristic of most deserts. High daytime temperatures give way to cold nights because there is no insulation provided byhumidity and cloud cover. The diversity of climatic conditions, though quite harsh, supports a rich array of habitats. Many of these habitats areephemeral in nature, reflecting the paucity and seasonality of available water.[1] Woody-stemmed shrubs and plants characterize vegetation in these regions. Above all, these plants have evolved to minimize water loss. Animal biodiversity is equally well adapted and quite diverse.[1]
Over millions of years, shifts in Earth's climate, including glacial and interglacial cycles, have caused deserts to expand and contract. Animal and plant life in these regions has evolved unique adaptations to survive in the harsh conditions. These adaptations include drought tolerance, specialized root systems and behaviors that minimize water loss.[citation needed]
Historically, humans have utilized deserts and xeric shrublands for resources likeminerals,salt andguano. Its exploitation has sometimes led to conflicts and changes in the landscape. Human settlements in desert regions have often focused onoases or areas with access to water sources. The development ofirrigation systems and other infrastructure has impacted the natural environment in these areas.[citation needed]
The conversion of productivedrylands to desert conditions, known asdesertification, can occur from a variety of causes. One is human intervention, including intensive agricultural tillage orovergrazing[4] in areas that cannot support such exploitation. Climatic shifts such asglobal warming or theMilankovitch cycle (which drivesglacials andinterglacials) also affect the pattern of deserts on Earth.
Xeric shrublands can experience woody plant encroachment, which is the thickening of bushes and shrubs at the expense of grasses.[5] This process is often caused by unsustainable land management practices, such as overgrazing and fire suppression, but can also be a consequence ofclimate change. As a result, the shrublands' coreecosystem services are affected, including its biodiversity, productivity, and groundwater recharge.[6] Woody plant encroachment can be an expression of land degradation.[7]
The World Wide Fund for Nature highlights a number of desertecoregions that have a high degree ofbiodiversity andendemism:[1]
This article incorporates text available under theCC BY-SA 3.0 license.World Wide Fund for Nature."Deserts and Xeric Shrubland Ecoregions". Archived fromthe original on 2012-04-25. Retrieved2019-05-29.
