Deserts and xeric shrublands

Desertic region at the M'Sila Province, Algeria

Extent of deserts and xeric shrublands

Deserts and xeric shrublands are a biome defined by the World Wide Fund for Nature.<ref name=wwf>Template:CC-notice Template:Cite web</ref> Deserts and xeric (Ancient Greek Template:Lang Template:Translit 'dry') shrublands form the largest terrestrial biome, covering 19% of Earth's land surface area.<ref>Template:Cite book</ref> Ecoregions in this habitat type vary greatly in the amount of annual rainfall they receive, usually less than Template:Convert annually except in the margins. Generally evaporation exceeds rainfall in these ecoregions. Temperature variability is also diverse in these lands. Many deserts, such as the Sahara, are hot year-round, but others, such as East Asia's Gobi Desert, become quite cold during the winter.<ref name=wwf/>

Temperature extremes are a characteristic of most deserts. High daytime temperatures give way to cold nights because there is no insulation provided by humidity and cloud cover. The diversity of climatic conditions, though quite harsh, supports a rich array of habitats. Many of these habitats are ephemeral in nature, reflecting the paucity and seasonality of available water.<ref name=wwf/> 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.<ref name=wwf/>

History

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.Template:Cn

Historically, humans have utilized deserts and xeric shrublands for resources like minerals, salt and guano. Its exploitation has sometimes led to conflicts and changes in the landscape. Human settlements in desert regions have often focused on oases or areas with access to water sources. The development of irrigation systems and other infrastructure has impacted the natural environment in these areas.Template:Cn

Degradation

Desertification

The Nama Karoo in South Africa is a xeric shrubland that receives between Template:Convert of rain a year.<ref>Template:Cite web</ref>

The conversion of productive drylands to desert conditions, known as desertification, can occur from a variety of causes. One is human intervention, including intensive agricultural tillage or overgrazing<ref>Template:Cite encyclopedia</ref> in areas that cannot support such exploitation. Climatic shifts such as global warming or the Milankovitch cycle (which drives glacials and interglacials) also affect the pattern of deserts on Earth.

Woody plant encroachment

Xeric shrublands can experience woody plant encroachment, which is the thickening of bushes and shrubs at the expense of grasses.<ref>Template:Cite journal</ref> This process is often caused by unsustainable land management practices, such as overgrazing and fire suppression, but can also be a consequence of climate change. As a result, the shrublands' core ecosystem services are affected, including its biodiversity, productivity, and groundwater recharge.<ref>Template:Citation</ref> Woody plant encroachment can be an expression of land degradation.<ref>Template:Cite journal</ref>

Ecoregions

The World Wide Fund for Nature highlights a number of desert ecoregions that have a high degree of biodiversity and endemism:<ref name=wwf/>

• The Nama Karoo of Namibia has the world's richest desert fauna.<ref>Template:Cite book</ref>
• The Carnarvon xeric shrublands of Australia are a regional center for endemism.<ref name=wwf/>
• The Chihuahuan desert may be the most biodiverse desert ecoregion in the world.<ref>Template:Cite book</ref>
• The Sonoran and Baja deserts of Mexico are unusual desert communities dominated by giant columnar cacti.<ref name=wwf/>
• Madagascar spiny forests
• Atacama Desert

See also

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• Xeriscaping — gardening or landscaping in xeric environments
• Xerocoles — animals adapted to xeric environments
• Xerophytes — plants adapted to xeric environments

External links

• Index to Deserts & Xeric Shrublands at bioimages.vanderbilt.edu
• Xeric World Online community focused on the study of xeric plant species
• Desert Plants: List, Names and Adaptations