The Ecohydrology of Desert Environments: What Makes it Distinctive?

The global arid lands, or drylands, can be loosely-defined in terms of precipitation and evapotranspiration, which characteristically result in semi-permanent water scarcity. This manifests itself in low soil moisture availability, ephemeral stream and river flow, and a plant cover that occupies only a part of the landscape. However, microphytic plants occupy many areas of otherwise bare soil where vascular plants are absent, and can confer some resistance to wind and water erosion. Dryland plants have developed some important adaptations to water scarcity, including the ability to capture rain and deliver it as stemflow to the soil around the base of the plant. There are also community-level adaptations that permit more abundant vegetation cover than might be expected in water-scarce environments. These include various kind of patchy vegetation, in which water is shed from bare areas and drains downslope to support localized groves of plants. A striking form of this adaptation that occurs in many parts of the global drylands is known as “tiger bush.” Drylands face ecohydrological change as global and regional climates change. A key issue that remains to be fully resolved is the extent to which dryland ecosystems are vulnerable to the effects of such change. In some ways that are discussed in this article, drylands may be seen as possessing some attributes that may in fact make them somewhat resilient to climate change.