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Summary Grasslands are located in areas with precipitation ranging between 150 and 1200 mm yr-1 and temperature between 0 and 25 C (Lieth and Whittaker, 1975). Along a precipitation gradient, in temperate regions, grasslands are located between forests and deserts. Sites with annual precipitation higher than 1200 mm yr-1 usually support forests whereas sites receiving less than 150 mm yr-1 usually are occupied by deserts. Temperature interacts with precipitation, moving the grassland-forest and grassland-desert boundaries to wetter or drier areas. For example, as temperature and potential evapotranspiration decrease, the grassland-forest boundary occurs at lower precipitation. In the Great Plains of North America where isohyets run in a north-south direction, the boundary between the tallgrass prairie and the temperate forest has a clear SE-NW direction (Barbour and Billings, 1988).