The primary factors that influence the formation of these biomes are climatic, like precipitation, temperature, seasonal extremes and winds. However, topography and light are also important factors. Of all these, precipitation is the chief limiting factor that determines whether a biome would be a forest or a desert or a grassland. If the average annual precipitation in the region is less than 25 cm the place would be a desert containing little vegetation. This would be true regardless of average temperature, light and quality of soil. If a region has moderate average precipitation, around 25-75 cm a year, grasslands would be formed. A region would be a forest if the average annual precipitation is more than 75 cm. The combination of average temperature and average precipitation, however, decides the type of desert, forest or grassland present in a region.