AFROTROPIC DESERTS

AUSTRALASIAN DESERTS

INDO-MALAY DESERTS

NEARCTIC DESERTS

NEOTROPIC DESERTS

PALEARCTIC DESERTS

True deserts are not the final stage of a process of desertification; they are unique, highly-adapted natural ecosystems. The desert biome includes arid and hyper-arid drylands, providing ecosystem services and supporting human populations that may degrade the land resources in much the same ways as in other ecosystems. The deserts of the world occur in six biogeographic realms. A summary of the main traits of the desert ecoregions within those realms is given in Appendices I and II, including desert type, area, area converted and under protection, species richness for various taxa, human density, and human footprint. A more detailed description of each ecoregion can be found at the National Geographic "Wild World" website (http://www.nationalgeographic.com/ wildworld/terrestrial.html) and at the World Wildlife Fund terrestrial ecoregions website (http://www. worldwildlife.org/science/ecoregions/biomes.cfm, see also Olson and others 2001). A short narrative description is given below, while a short description on the evolutionary origin of desert biodiversity is given in Box 4.1.