They are covered with tall grasses. They may have scattered bushes and trees, but not enough to keep grasses from growing. The most common definition of savanna is the tropical grassland, such as in Africa. They have seasonal rains and dry periods. All savanna plants and trees can survive periods of drought. Most savannas get enough rain to support the forest, but the forest never happens because something keeps the trees from growing. This can be animals that graze and knock over trees (like elephants in Africa), or fires that kill most kinds of trees. Instead there is lots of grasses and other plants that can regrow from the roots.