Deserts and xeric shrublands

{{short description|Biome with 250 mm of annual rainfall or less}}

{{redirect|Xeric|the comic book grant foundation|Xeric Foundation}}

Deserts and xeric shrublands are a biome defined by the World Wide Fund for Nature.{{CC-notice|bysa3}} {{cite web|archive-url=https://web.archive.org/web/20120425205057/http://wwf.panda.org/about_our_earth/ecoregions/about/habitat_types/selecting_terrestrial_ecoregions/habitat13.cfm|archive-date=2012-04-25|url=http://wwf.panda.org:80/about_our_earth/ecoregions/about/habitat_types/selecting_terrestrial_ecoregions/habitat13.cfm|title=Deserts and Xeric Shrubland Ecoregions|author=World Wide Fund for Nature|access-date=2019-05-29|url-status=dead}} Deserts and xeric (Ancient Greek {{lang|grc|ξηρός}} {{translit|grc|xērós}} 'dry') shrublands form the largest terrestrial biome, covering 19% of Earth's land surface area.{{cite book|last=Lockwood|first=M.|title=Managing Protected Areas: A Global Guide|page=199}} Ecoregions in this habitat type vary greatly in the amount of annual rainfall they receive, usually less than {{convert|10|in|mm|order=flip}} 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.

Degradation

=Desertification=

File:Sengi-landscape Nama Karoo.tif in South Africa is a xeric shrubland that receives between {{convert|100|and|500|mm|in|0}} of rain a year.{{cite web|url=https://www.worldwildlife.org/ecoregions/at1314|title=Nama Karoo|publisher=WWF|access-date=2018-12-19}}]]

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{{cite encyclopedia|first=C. Michael|last=Hogan|year=2009|url=https://editors.eol.org/eoearth/wiki/Overgrazing|title=Overgrazing|encyclopedia=Encyclopedia of Earth|editor-first1=Sidney|editor-last1=Draggan|editor-first2=Cutler J.|editor-last2=Cleveland|publisher=National Council for Science and the Environment|location=Washington, D.C.}} 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.{{Cite journal|last1=Eldridge|first1=David J.|last2=Bowker|first2=Matthew A.|last3=Maestre|first3=Fernando T.|last4=Roger|first4=Erin|last5=Reynolds|first5=James F.|last6=Whitford|first6=Walter G.|date=July 2011|title=Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis: Synthesizing shrub encroachment effects|journal=Ecology Letters|language=en|volume=14|issue=7|pages=709–722|doi=10.1111/j.1461-0248.2011.01630.x|pmc=3563963|pmid=21592276}} 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.{{Citation|last1=Archer|first1=Steven R.|title=Woody Plant Encroachment: Causes and Consequences|date=2017|work=Rangeland Systems|pages=25–84|editor-last=Briske|editor-first=David D.|place=Cham|publisher=Springer International Publishing|language=en|doi=10.1007/978-3-319-46709-2_2|isbn=978-3-319-46707-8|last2=Andersen|first2=Erik M.|last3=Predick|first3=Katharine I.|last4=Schwinning|first4=Susanne|last5=Steidl|first5=Robert J.|last6=Woods|first6=Steven R.|series=Springer Series on Environmental Management |s2cid=133015720 |doi-access=free}} Woody plant encroachment can be an expression of land degradation.{{Cite journal|last1=Schlesinger|first1=William H.|last2=Reynolds|first2=James F.|last3=Cunningham|first3=Gary L.|last4=Huenneke|first4=Laura F.|last5=Jarrell|first5=Wesley M.|last6=Virginia|first6=Ross A.|last7=Whitford|first7=Walter G.|date=1990-03-02|title=Biological Feedbacks in Global Desertification|url=https://www.science.org/doi/10.1126/science.247.4946.1043|journal=Science|language=en|volume=247|issue=4946|pages=1043–1048|doi=10.1126/science.247.4946.1043|pmid=17800060 |bibcode=1990Sci...247.1043S |s2cid=33033125 |issn=0036-8075|url-access=subscription}}

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.{{cite book|last1=Cowling|first1=RM|first2=C|last2=Hilton-Taylor|year=1994|chapter=Patterns of plant diversity and endemism in southern Africa: An overview|pages=31–52|editor-first=BJ|editor-last=Huntley|title=Botanical diversity in southern Africa|publisher=National Botanical Institute|location=Pretoria, South Africa}}
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.{{Cite book|title=Terrestrial ecoregions of North America : a conservation assessment|year=1999|last1=Ricketts|first1=TH|first2=E|last2=Dinerstein|first3=DM|last3=Olson|display-authors=et al|publisher=Island Press|location=Washington, DC|isbn=1-55963-722-6|page=44}}
The Sonoran and Baja deserts of Mexico are unusual desert communities dominated by giant columnar cacti.
Madagascar spiny forests
Atacama Desert

References

External links

[https://web.archive.org/web/20120905010259/http://www.cas.vanderbilt.edu/bioimages/ecoframe-list.htm Index to Deserts & Xeric Shrublands at bioimages.vanderbilt.edu]
[https://web.archive.org/web/20090129105807/http://www.xericworld.com/forums/ Xeric World] Online community focused on the study of xeric plant species
[https://sand-boarding.com/desert-plants/ Desert Plants: List, Names and Adaptations]

Category:Terrestrial biomes

Category:Flora of the California desert regions