Deserts Deserts are places where there is less than 250 mm annual precipitation. Plant cover is sparse, and characterized by drought tolerant brushes, succulent and annual plants. The soil is very poor in nutrients, and the humus layer is absent or only weakly developed. There is 900-1500 mm of rain each year, with a pronounced wet or rainy, and an almost equally long dry season. The temperatures are high year long, which results in droughts during the dry season, when most plants die or dry out.
Soils are relatively nutrient poor due to leaching out during the rainy seasons.
Trees are widely spaced, and the majority of the vegetation is different species of grasses. Fire is important in the maintenance of the savanna, and many plant species are fire tolerant, or even require fire for growth and germination. Tropical rainforests Tropical rainforests occur close to the Equator, where temperature fluctuates only little, and the precipitation is more or less evenly distributed throughout a year. Due to the excess rainfall and rapid decomposition, the soils are very devoid of nutrients. The vegetation is lush with many layers in the canopy that support an incredible diversity of life.