The Savanna Grassland Biome

What is a savanna?

A savanna is a warm grassland scattered with trees. Picture wide, golden plains of grass stretching to the horizon, broken up by the occasional flat-topped acacia tree — that is the classic African savanna. Savannas sit between two other biomes: the wet tropical rainforests near the equator and the dry deserts further away. They get more rain than a desert but not enough to grow a dense forest, which is why grass, rather than trees, rules the land.

The biggest savannas are in Africa, including the famous Serengeti, but they are also found in South America, India and northern Australia.

A land of two seasons

Unlike places with four seasons, a savanna has just two main ones, both warm:

• The wet season. Rains arrive, the dry grass turns green and grows fast, water holes fill, and animals have plenty to eat.
• The dry season. For many months little or no rain falls. The grass dries to gold, rivers and water holes shrink, and food and water become scarce.

This strong rhythm of plenty and scarcity shapes everything that lives there. To compare it with a place that has milder seasons, see the four seasons.

Grass: the foundation of life

Grasses are the producers at the base of the savanna's food web. They capture sunlight through photosynthesis and turn it into food. What makes savanna grasses so tough is where they grow from: their growing point sits at the base of the plant, near the soil. So when an animal bites off the top, or a fire sweeps through, the grass can quickly grow new blades. This is why grass survives constant grazing that would kill many other plants.

That endless supply of grass feeds enormous herds of grazing animals — zebras, wildebeest, antelope and buffalo. These in turn feed some of the world's most famous predators: lions, cheetahs, leopards and hyenas. When animals die, scavengers like vultures and decomposers clean up, returning nutrients to the soil.

Built to survive

Life on the savanna must cope with drought, fire and being eaten. Plants and animals have clever adaptations:

• Acacia trees have deep roots to reach water far underground, small waxy leaves to reduce water loss, and sharp thorns to protect themselves from hungry browsers like giraffes.
• Grazing herds migrate long distances, following the rains to find fresh grass and water. The wildebeest migration in East Africa, over a million animals strong, is one of the greatest wildlife spectacles on Earth.
• Many animals are built for speed — both predators chasing prey and prey escaping across the open plains, where there is nowhere to hide.
• Some animals store water or fat, or stay still during the hottest hours and feed in the cool of dawn and dusk.

The role of fire

It may seem strange, but fire is a natural and healthy part of the savanna. During the dry season, lightning can set the dead grass alight. These fires burn off old, dry growth and kill many young tree seedlings before they can grow tall. This keeps the savanna open and grassy — without regular fire, trees would gradually take over and turn it into woodland. After the rains return, the grass grows back greener than before, refreshed by nutrients in the ash.

Savannas and people

Savannas are home to many people and their livestock, and they hold some of the planet's most treasured wildlife. But they face threats from farming, overgrazing and climate change. Protecting savanna national parks and reserves helps safeguard the herds, predators and grasses that make this biome so remarkable. You can read more about protecting wild places in biodiversity and conservation.

Try it yourself: a savanna seasons diary

Get a feel for how the wet and dry seasons drive savanna life.

1. Draw two large boxes on a page, labelled "Wet Season" and "Dry Season."
2. In the wet season box, draw green grass, full water holes, and animals spread out feeding.
3. In the dry season box, draw golden dry grass, a shrinking water hole, and a herd crowding around it.
4. Around each picture, write three things an animal must do to survive that season — for example, "store fat," "migrate to find water," or "stay near the shrinking pool."

Comparing your two pictures shows why savanna animals are constantly on the move and so well adapted to a world that swings between feast and drought.