Earth: Savannah

Maria is travelling in Africa. Today she is going on a day trip with a guide. As they're driving through the dry grassy landscape dotted with occasional trees, the guide tells her this is the savannah. The savannah covers vast areas of land around the equator - in a tropical or subtropical climate. These areas are typically a transition zone between hot, humid rainforests and deserts.

The biggest savannahs are found in Africa, but there are smaller ones in South and Central America, Southeast Asia and northern Australia as well. In total, savannah covers about 20% of the Earth’s land surface. Although the savannah on different continents has different typical plants and animals, there are some elements that all these regions have in common. Being close to the equator, the savannah stays quite warm all year round, but we can distinguish between two seasons. Most of the year is the dry season, during which there is very little or no rain, and the temperature is about ten to twenty degrees Celsius.

In the dry season, grasses and leaves dry out, making the landscape yellow and bare. As soon as rain falls, all vegetation grows back again, turning the savannah into green plains bursting with life again. This happens south of the equator between October and March, and north of the equator between April and September. This is the rainy season. Practically all yearly rainfall falls during this time.

The average temperature during the rainy season is twenty to thirty degrees Celsius. Only plants that can survive long periods of drought can grow in these conditions. Grasses, trees and bushes here are adapted to make the best use of seasonally available water. For example, acacia trees have roots that grow very deep in the ground and can draw water from groundwater sources, and baobab trees can store water in their massive trunks. Plentiful grass and other plants are a great source of food for all kinds of herbivores.

Maria can see herds of zebras and antelopes, grazing on the grass. She’s hoping to see elephants and giraffes too. All these animals can exist and thrive together in the same area, because they have different food preferences. They find food at different heights, or during a different time of day or year. Herbivores shape the open landscape by limiting the spread and growth of bushes and trees.

Such landscape makes it easier for birds of prey, such as hawks or eagles, to spot their prey. The landscape also allowed predators of the savannah - lions or cheetahs, to evolve into some of the fastest animals on Earth. The animals they hunt: gazelles, ostriches, and wildebeests, need to run really fast too, to avoid being eaten. Dead animals and their remains are often eaten by scavengers, such as hyenas or vultures. And whatever is left over is quickly broken down into nutrients by insects, worms, fungi and bacteria - the decomposers.

These nutrients end up in the soil, allowing plants to grow back. Unfortunately, farmers use the savannah to grow crops, or as a grazing area for cattle. Farming takes away space and food from the organisms that naturally live here, forcing them to move, or even causing them to die. Overgrazing and crops often destroy the natural grass cover. This causes soil to be washed away by rain, or be stripped away by wind.

The land becomes bare and desert-like. Savannas are some of the most diverse and interesting ecosystems on the planet. Maria can’t wait to show pictures from the trip to her friends.