Extent of deserts and xeric shrublands
Extent of deserts and xeric shrublands

Deserts and xeric shrublands are a biome defined by the World Wide Fund for Nature.[1] Deserts and xeric (ancient Greek xērós, “dry") shrublands form the largest terrestrial biome, covering 19% of Earth'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 the Sahara, are hot year-round, but others, such as East Asia's Gobi, become quite cold in winter.[1]

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.[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]

Degradation

Desertification

Main article: Desertification

The Nama Karoo in South Africa is a xeric shrubland that receives between 100 and 500 millimetres (4 and 20 in) of rain a year.[3]
The Nama Karoo in South Africa is a xeric shrubland that receives between 100 and 500 millimetres (4 and 20 in) of rain a year.[3]

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[4] 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.[5] This process is often caused by unsustainable land management practices, such as overgrazing and fire suppression, but also a consequence of climate change. As a result, core ecosystem services of the shrublands are affected, including its biodiversity, productivity and groundwater recharge.[6] Woody plant encroachment can be an expression of land degradation.[7]

Ecoregions

See also: List of desert and xeric shrubland ecoregions

The World Wide Fund for Nature highlights a number of desert ecoregions that have a high degree of biodiversity and endemism:[1]

See also

References

  1. ^ a b c d e f g  This article incorporates text available under the CC BY-SA 3.0 license. World Wide Fund for Nature. "Deserts and Xeric Shrubland Ecoregions". Archived from the original on 2012-04-25. Retrieved 2019-05-29.
  2. ^ Lockwood, M. Managing Protected Areas: A Global Guide. p. 199.
  3. ^ "Nama Karoo". WWF. Retrieved 2018-12-19.
  4. ^ Hogan, C. Michael (2009). "Overgrazing". In Draggan, Sidney; Cleveland, Cutler J. (eds.). Encyclopedia of Earth. Washington, D.C.: National council for Science and the Environment.
  5. ^ Eldridge, David J.; Bowker, Matthew A.; Maestre, Fernando T.; Roger, Erin; Reynolds, James F.; Whitford, Walter G. (July 2011). "Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis: Synthesizing shrub encroachment effects". Ecology Letters. 14 (7): 709–722. doi:10.1111/j.1461-0248.2011.01630.x. PMC 3563963. PMID 21592276.
  6. ^ Archer, Steven R.; Andersen, Erik M.; Predick, Katharine I.; Schwinning, Susanne; Steidl, Robert J.; Woods, Steven R. (2017), Briske, David D. (ed.), "Woody Plant Encroachment: Causes and Consequences", Rangeland Systems, Cham: Springer International Publishing, pp. 25–84, doi:10.1007/978-3-319-46709-2_2, ISBN 978-3-319-46707-8, S2CID 133015720, retrieved 2021-12-10
  7. ^ Schlesinger, William H.; Reynolds, James F.; Cunningham, Gary L.; Huenneke, Laura F.; Jarrell, Wesley M.; Virginia, Ross A.; Whitford, Walter G. (1990-03-02). "Biological Feedbacks in Global Desertification". Science. 247 (4946): 1043–1048. Bibcode:1990Sci...247.1043S. doi:10.1126/science.247.4946.1043. ISSN 0036-8075. PMID 17800060. S2CID 33033125.
  8. ^ Cowling, RM; Hilton-Taylor, C (1994). "Patterns of plant diversity and endemism in southern Africa: An overview". In Huntley, BJ (ed.). Botanical diversity in southern Africa. Pretoria, South Africa: National Botanical Institute. pp. 31–52.
  9. ^ Hernandez, HM; Barcenas, RT (1995). "Endangered cacti in the Chihuahuan Desert: I. Distribution patterns". Conservation Biology. 9 (5): 1176–1188. doi:10.1046/j.1523-1739.1995.9051169.x-i1. PMID 34261239.