The savanna is a unique global biome, often envisioned as the vast, open plains of Africa, yet it is found on multiple continents. This ecosystem represents a transitional zone situated between tropical forests and deserts. Characterized by a continuous layer of grass interspersed with scattered trees, the savanna is defined by the seasonality of its rainfall, not a lack of rain. This distinct structure and climate support some of the planet’s most iconic wildlife and diverse human cultures, spanning nearly 20% of the Earth’s land area.
Defining the Savanna Ecosystem
The savanna ecosystem is defined by a climate featuring pronounced wet and dry seasons. A typical savanna experiences a wet summer lasting six to eight months, followed by a dry winter persisting for four to six months. This seasonal fluctuation prevents the establishment of a continuous forest canopy, as trees cannot access sufficient water year-round to grow densely. The vegetation structure is dominated by a dense, continuous understory of grasses that thrive during the wet season, while trees, like the baobab or acacia, are scattered and widely spaced, creating an open canopy that allows ample sunlight to reach the ground level. The dry season also makes the environment prone to fires, which regularly clear out woody seedlings and old grass, maintaining the grassland-tree mosaic.
Global Geographic Distribution
Savannas are distributed across the tropics and subtropics, with the largest concentration in Africa. The African savanna covers almost half the continent, extending in a wide band from the Atlantic coast, known as the Sudano-Sahelian belt, across to the Ethiopian Highlands. Major areas include the vast plains of East Africa, such as the Serengeti in Tanzania and the Maasai Mara in Kenya, renowned for their massive migratory herds. Further south, countries like South Africa and Botswana contain extensive savanna landscapes.
South America hosts significant savanna regions that differ in species composition from their African counterparts. The Cerrado in central Brazil represents the world’s most biodiverse savanna, covering over 2 million square kilometers. North of the Amazon, the Llanos—a tropical grassland that floods seasonally—is found primarily in Venezuela and Colombia. In Australia, tropical savannas dominate the northern third of the continent, extending from the Kimberley region to Queensland. These Australian savannas feature sclerophyllous vegetation, like eucalyptus and acacia, adapted to the seasonal monsoonal climate.
Unique Wildlife Adaptations
Survival in the savanna requires specialized adaptations to cope with the dramatic shift between drought and deluge, and the constant threat of fire. Many large herbivores, such as wildebeest and zebra, employ long-distance migration, following seasonal rains to find fresh grass and water. This movement ensures access to resources that would otherwise be depleted during the dry season. Smaller animals often rely on camouflage, like the dusty-beige coat of a lion or the striped pattern of a zebra, which helps them blend into the open landscape.
Plant life exhibits mechanisms for enduring long periods of aridity and frequent grass fires. Many grasses have growth tissue located close to the ground, allowing them to rapidly regrow after being grazed or burned. Their deep, fibrous root systems anchor them and access deep groundwater. Trees like the baobab have developed thick, corky bark that resists fire damage and a massive trunk that stores water for use during the dry months. Other trees, such as the acacia, develop extensive taproots that reach the water table, and some drop their leaves completely during the dry season to minimize water loss.
Human Use and Conservation
Savanna ecosystems have supported human populations for millennia, with traditional activities centered on pastoralism and agriculture tailored to the seasonal climate. Many communities depend on the grasslands for grazing livestock, where nomadic movement historically allowed the land to recover. For example, the collection of Gum Arabic from acacia trees in the Sudan region provides an income source and a global commodity used in pharmaceuticals and food production. The biodiversity also fuels a wildlife tourism industry, contributing substantially to the economies of countries like Kenya and Tanzania.
Modern pressures have introduced conservation challenges to these environments. Expanding human populations lead to habitat loss as savannas are converted to commercial farms for cash crops like corn or soybeans, or fragmented by infrastructure development. Overgrazing by concentrated livestock populations can strip the land of vegetation, accelerating soil degradation and erosion. Changes to the natural fire regime, through either suppression or careless ignition, can disrupt the ecological balance that the savanna’s flora and fauna have evolved to depend on.