Savannahs are a planned biome.
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of grasses. Some classification systems[which?] also recognize a grassland savanna from which trees are absent. This article deals only with savanna under the common definition of a grassy woodland with a significant woody plant component. It is often believed that savannas feature widely spaced, scattered trees. However, in many savannas, tree densities are higher and trees are more regularly spaced than in forest. Savannas are also characterized by seasonal water availability, with the majority of rainfall confined to one season. Savannas are associated with several types of biomes. Savannas are frequently in a transitional zone between forest and desert or grassland. Savanna covers approximately 20% of the Earth's land area.
This article was taken from wikipedia.