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Deserts and xeric shrublands also called xerófila are a biome characterized by, relating to, or requiring only a small amount of moisture,〔(Merriam-Webster.com ) Merriam-Webster Dictionary definition of xeric〕 usually defined as less than 250 mm of annual precipitation. It is the largest terrestrial biome, covering 19% of the earth's land surface area. They may be further characterized as hyperxerófila (very dry) and hypoxerófila (less dry). ==Character of the biome== (詳細はendemism in some regions. ''Minimum resources'': Many species track seasonally variable and patchy resources and require large natural landscapes to persist. Available water sources and riparian habitats are critical for the persistence of many species. ''Poor soils'': Because biomass productivity is low, the litter layer is almost nonexistent and the organic content of surface soil layers is very low. Also, evaporation tends to concentrate salts at the soil surface. ''Sensitivity to disturbance'': As the desert is highly sensitive to grazing, soil disturbance, burning, plowing, and other cover alteration; restoration potential can be very low and regeneration very slow. The introduction of exotic species may be a serious problem. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Deserts and xeric shrublands」の詳細全文を読む スポンサード リンク
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