ABSTRACT
Deserts occupy about 30% of the global ice-free landmass. Potential evapotranspiration exceeds precipitation during most days of the year, and the biome shows the greatest contrast in temperature, both diurnal and seasonal. Desert vegetation is very sparse with a few isolated shrubs dominated by succulents and annuals. Grasses and forbs become more dominant at the margins. The tropics occupy about 27% of the landmass and are characterized by only a small variation in temperature during the year. The soil moisture conditions range from semiarid to humid. The availability of soil moisture determines the biota. The temperate grassland and forest biome occupies about 15%. The cold biomes, the boreal and polar, are mainly in the northern latitudes with small areas in South America. The low temperatures control the fl ora and fauna, and vegetation is scarce to nonexistent in the extreme cold polar regions. Each of these areas has specifi c kinds of soils that have developed as a response to the specifi c soil moisture and temperature conditions. The diversity in vegetation has its equivalent in fauna with animal species adapting to the specifi c bio-climatic conditions. Within each of the biomes, there are specifi c conditions that promote unique fl ora and fauna. Examples of such localized systems are volcanic hot springs, wetlands, and oases.
