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Deserts and xeric shrublands

Biome with 250 mm of annual rainfall or less

Extent of deserts and xeric shrublands

Deserts and xeric shrublands are a biome defined by the World Wide Fund for Nature. Deserts and xeric (Ancient Greek ξηρός 'dry') shrublands form the largest terrestrial biome, covering 19% of Earth's land surface area. Ecoregions in this habitat type vary greatly in the amount of annual rainfall they receive, usually less than 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 the Sahara, are hot year-round, but others, such as East Asia's Gobi Desert, become quite cold during the winter.

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. 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.

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.

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.

Degradation

Desertification

Main article: Desertification

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 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

Main article: Woody plant encroachment

Xeric shrublands can experience woody plant encroachment, which is the thickening of bushes and shrubs at the expense of grasses. 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. Woody plant encroachment can be an expression of land degradation.

Ecoregions

The World Wide Fund for Nature highlights a number of desert ecoregions that have a high degree of biodiversity and endemism:

The Nama Karoo of Namibia has the world's richest desert fauna.
The Carnarvon xeric shrublands of Australia are a regional center for endemism.
The Chihuahuan desert may be the most biodiverse desert ecoregion in the world.
The Sonoran and Baja deserts of Mexico and the United States are unusual desert communities dominated by giant columnar cacti.
Madagascar spiny forests
Atacama Desert

References

World Wide Fund for Nature. "Deserts and Xeric Shrubland Ecoregions".
Lockwood, M.. "Managing Protected Areas: A Global Guide".
"Nama Karoo". WWF.
Hogan, C. Michael. (2009). "Overgrazing". National Council for Science and the Environment.
(July 2011). "Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis: Synthesizing shrub encroachment effects". Ecology Letters.
(2017). "Woody Plant Encroachment: Causes and Consequences". Springer International Publishing.
(1990-03-02). "Biological Feedbacks in Global Desertification". Science.
(1994). "Botanical diversity in southern Africa". National Botanical Institute.
(1999). "Terrestrial ecoregions of North America : a conservation assessment". Island Press.

Info: Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

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