A savanna is a landscape defined by open grassland with scattered trees, where tree canopy covers roughly 10% to 50% of the ground. That mix of grass and sparse tree cover sets savannas apart from both dense forests and treeless plains. They exist on every continent except Antarctica, covering half the surface of Africa and large stretches of Australia, South America, and India. Globally, savannas rank among the most widespread terrestrial ecosystems on Earth.
What Makes a Savanna Different From a Forest or Grassland
The simplest way to picture a savanna is to imagine standing in a wide field of tall grasses where you can see the horizon, but individual trees or small clusters of trees dot the landscape at irregular intervals. In a forest, the tree canopy closes overhead and blocks most sunlight from reaching the ground. In a pure grassland, trees are essentially absent. A savanna sits between these two extremes, with tree cover of at least 10% but no more than 50%.
This open structure shapes everything about the ecosystem. Sunlight reaches the ground easily, fueling thick grass growth. The grasses, in turn, provide fuel for fire, which keeps tree populations in check. It’s a self-reinforcing cycle: enough trees to provide shade and food for animals, enough open space for grasses to dominate, and enough fire to prevent the landscape from becoming forest.
Climate and Rainfall Patterns
Savannas form in tropical and subtropical regions with strongly seasonal rainfall. Annual precipitation typically falls between 300 and 1,500 millimeters (about 12 to 60 inches), which places savannas in the zone between deserts and tropical rainforests. The defining feature isn’t total rainfall but how unevenly it arrives. In some savannas, an entire year’s worth of rain can fall within just a few weeks.
For at least five months of the year, during the dry season, rainfall drops below about 100 millimeters (4 inches) per month. This prolonged dry period is what prevents most tree species from taking over. Grasses can go dormant during drought and bounce back quickly when rains return. Most tree species can’t handle that cycle as well, which is one reason the landscape stays open rather than filling in with forest.
Soils That Favor Grass Over Trees
Savanna soils play a surprisingly large role in keeping the landscape open. In tropical savannas, the dominant soil-forming process creates laterite, a type of soil that hardens into a brick-like layer when exposed to cycles of wetting and drying. During the rainy season, water pools above this hardened layer, waterlogging the ground for months and drowning tree roots. During the dry season, the same layer blocks roots from reaching deeper moisture.
These soils tend to be acidic, often with a pH between 4 and 5, and relatively low in key nutrients like nitrogen and phosphorus. Potassium is usually the most abundant nutrient. Sandy or volcanic substrates in some regions create similarly dry, nutrient-poor conditions that grasses tolerate far better than trees do. The result is a landscape where soil chemistry and structure actively work against forest development.
Fire as an Ecosystem Engine
Fire is not a disaster in a savanna. It is one of the forces that creates and maintains the ecosystem. Dry grasses ignite easily, and periodic burns sweep across the landscape during the dry season, killing young tree seedlings before they can grow tall enough to survive. Mature savanna trees have evolved thick, insulating bark that protects them from these low-intensity fires, so established trees survive while new ones struggle to gain a foothold.
Long-term studies from the U.S. Forest Service show that frequent fire use stimulates growth and development of the rich understory plant community, reduces competing vegetation, and maintains the biological diversity characteristic of savanna-type ecosystems. Without fire, many savannas would gradually transition into closed-canopy woodland or forest. This is why land managers around the world use controlled burns to preserve savanna habitats.
How Plants Survive Drought and Grazing
Savanna plants have evolved a toolkit of strategies to handle the constant stress of drought, fire, and grazing. Perennial grasses develop deep root systems that reach water in lower soil layers, while annual grasses concentrate their roots near the surface to quickly capture rainfall before it evaporates. Dense perennial grass cover also protects topsoil from heat-driven water loss and erosion, benefiting the entire plant community.
When drought intensifies or grazing pressure increases, the mix of grass species shifts. Drought-resistant and grazing-tolerant species become more dominant, replacing less hardy varieties. This built-in flexibility makes savannas remarkably resilient. Research shows that savannas with a diverse mix of plant types and a healthy population of both grazing and browsing animals are the most resistant to drought, because different species fill different ecological roles and buffer the system against stress.
Wildlife and Keystone Species
Savannas support some of the most iconic wildlife concentrations on Earth. The African savanna is home to large herds of zebras, wildebeest, and gazelles, along with predators like lions, cheetahs, and hyenas. South American savannas (called the cerrado and llanos) host capybaras, jaguars, and giant anteaters. Australian savannas support kangaroos, wallabies, and a wide range of reptiles and birds.
African savanna elephants are a prime example of what ecologists call ecosystem engineers. Rather than simply living in the savanna, elephants actively reshape it. They knock down trees, keeping the landscape open. They dig for water during dry periods, creating pools that other animals depend on. Through their dung, they spread plant seeds across vast distances, and some plant species have evolved seeds that actually germinate more easily after passing through an elephant’s digestive system. The loss of elephants to poaching doesn’t just reduce one species; it changes the physical structure of the entire landscape.
Carbon Storage Below the Surface
Savannas store carbon differently than forests do. In a forest, most carbon sits in the trunks, branches, and leaves of trees. In a savanna, the vast majority of carbon is locked underground in the soil. Research in Sudanese woodland savanna found that soil organic carbon averaged about 5,453 grams of carbon per square meter in the top meter of soil, while above-ground tree biomass held only about 112 grams per square meter. That means the soil stored roughly 50 times more carbon than the visible vegetation above it.
This matters for conservation. When savannas are plowed for agriculture or overgrazed to the point of soil degradation, the carbon released comes primarily from the soil, a reservoir that took centuries to build. Protecting savanna soils is, in carbon terms, far more important than protecting the scattered trees above them.
Threats From Agriculture and Land Conversion
Savannas are under significant pressure worldwide. In southern Africa’s grassland and savanna biome, roughly 39% of the landscape has been permanently modified, primarily by agriculture. Cultivated land accounts for about 27% of the converted area, with forest plantations and human settlements making up the rest. Between 1986 and 2020, sparse natural vegetation (equivalent to indigenous grassland) lost 31.5% of its cover.
At the same time, areas that were once open savanna are experiencing bush encroachment, where woody shrubs and dense vegetation spread into formerly grassy landscapes. Dense vegetation cover increased by nearly 25% over that same period. Bush encroachment is driven by a combination of factors: overgrazing that removes grasses, fire suppression that allows woody plants to establish, and changes in rainfall patterns. The result is a landscape that looks superficially “greener” but has lost the open structure, biodiversity, and ecological function of a true savanna.
Where the Major Savannas Are
Africa holds the largest savanna systems on the planet, covering roughly half the continent. The Serengeti in East Africa is the most famous, but vast savannas stretch across West Africa’s Sahel region, southern Africa, and Madagascar. In South America, the Brazilian cerrado is one of the world’s most biodiverse savannas, while the llanos of Venezuela and Colombia flood seasonally to create a unique wetland-savanna hybrid. Australia’s tropical savannas span the northern third of the continent, forming one of the largest intact savanna landscapes remaining on Earth. India’s savannas, while less well known, cover significant areas of the Deccan Plateau and central regions, supporting species like the Indian bison and blackbuck.