6.2.13. Deserts and xeric shrublands

the_desert_-climateWorldwide, Deserts and Xeric Shrublands vary greatly in the amount of annual rainfall they receive; generally, however, evaporation exceeds rainfall in these ecoregions, usually less than 10 inches annually. Temperature variability is also extremely diverse in these remarkable lands. Many deserts, such as the Sahara, are hot year-round but others, such as Asia’s Gobi, become quite cold in winter.

desert_9 desertTemperature extremes are a characteristic of most deserts. Searing daytime heat gives way to cold nights because there is no insulation provided by humidity and cloud cover. Not surprisingly, 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.

The Namib-Karoo deserts of southwestern Africa support the world’s richest desert floras, while the Chihuahuan Desert and central Mexican deserts are a close second and are the richest Neotropical deserts. Australian deserts support the richest reptile faunas. The Carnavon Xeric Scrub of western Australia is a regional center of endemism for a range of taxa.

Unusual desert communities dominated by giant columnar cacti occur in the Sonoran and Baja deserts of North America, while the spiny deserts and shrublands of southwestern Madagascar are globally unique in terms of structure and taxa (although some Baja California communities are partially convergent in structure).

The Atacama Desert ecoregion of western South America (as well as the adjacent transition area of the Monte / Puna / Yungas) and the Horn of Africa deserts were recognized as some of the more outstanding regional centers of richness and endemism. The Central Asian deserts, while not nearly as rich as Afrotropical or Neotropical deserts, are representative of the region’s deserts.

Biodiversity Patterns
Deserts and xeric shrublands may have extraordinarily rich floras with very high alpha and beta diversity; reptile faunas may also be very diverse; local endemism may be quite pronounced in some regions.

Minimum Requirements
Many species track seasonally variable and patchy resources and require large natural landscapes to persist; water sources and riparian habitats are critical for the persistence of many species.

Sensitivity to Disturbance
Highly sensitive to grazing, soil disturbance, burning, plowing, and other cover alteration; restoration potential can be very low and regeneration very slow; exotic species may be a serious problem.

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