There are grasslands on nearly every continent. Some are temperate grasslands barren of trees and some are savannas, but all grasslands face some of the same ecological problems. In Africa, these problems come from natural occurrences, human encroachment and the disruption of the natural ecosystems that have been in place on the grasslands for years.
Savanna grasses, and in turn the animals that live in the grassland, are dependent on regular rainfall for survival. Many grasslands have a dry season and a rainy season, which occur with some regularity from year to year. During the dry season, many plants may shrivel and die above ground to be regrown from roots when the rains come. Animals such as zebra and antelope gauge their reproductive cycle around the rains, giving birth at the start of the rainy season to ensure there is enough food for adult animals and, in turn, the young. If the rains do not come, or if they are not as heavy as usual, this can cause food to be scarce and may result in the death of starving young.
The soils of the grasslands are generally fertile, supporting a myriad of different types of plants that in turn feed the animals that live there. Continued soil health relies on nutrients that are replenished by rainfall and by runoff from rivers; in the savanna grasslands of Africa areas are most fertile around these valuable rivers. These are the areas most often turned to farmland, and continued farming can quickly deplete nutrients.
With the development of towns and villages, dams have been built and rivers have been redirected, resulting in additional loss of fertile land. These effects go all the way up the food chain, making the land provide less food for animals and less animals for the people who live there to hunt. This loss of grass and plant life can also make it difficult for those who graze livestock on the land, relying on these creatures for meat, milk, leather and wool.
Around grasslands, there are typically areas that can support tree life. These forests support different ecosystems than the grasslands; for example, there are not wide plains for animals like zebras to roam, or the large, hoofed game that predators like lions and hyenas survive on. The seeds of trees are spread by the elements or by birds and other small animals; as these seeds take root and grow, areas that were previously thin forest become more thickly populated and the lines between grassland and forest begins to move.
Across Africa, tree plantations are being deliberately planted by towns, villages and families who rely on the wood or fruits for survival and income, also reducing the amount of grasslands available. The climate is ideal for trees such as commercially harvested eucalyptus.
Invasive plants can be introduced to an environment in a number of ways, from being planted by people to accidentally having seeds introduced in animal feed. The plant species can often crowd out native plants, which can be a food source for native African herbivores such as antelope, zebras and giraffes. If these invasive plants are hardier than the native types, they can quickly overrun the native population -- doubly problematic if there are only a few native plants that species of birds or animals feed on. For example, the giraffe has adapted to feed primarily on the tall acacia trees; a threat to these trees can impact the giraffe population. Invasive species have been found to grow particularly well in areas that have been disturbed by disasters such as fire and flood, growing back well before other, native species can regain a foothold.