A savanna is a warm, grassy landscape dotted with scattered trees, covering more than one-fifth of Earth’s land surface. What sets it apart from a pure grassland or a dense forest is the mix: grasses dominate the ground, but trees are spaced widely enough that sunlight reaches the soil, typically with canopy cover ranging from about 5% to 80%. This coexistence of trees and grasses, shaped by seasonal rainfall, fire, and grazing animals, is what defines the savanna.
Where Savannas Are Found
The most famous savannas stretch across sub-Saharan Africa, from the Serengeti in East Africa to the vast bushveld of southern Africa. But savannas exist on nearly every continent. South America has the Brazilian cerrado and the Venezuelan and Colombian llanos. Australia’s tropical north is largely savanna. Parts of India and Southeast Asia support savanna-like landscapes, and even small pockets exist in the southern United States.
What all these regions share is warmth and a strongly seasonal climate. Savannas receive roughly 50 to 127 centimeters (20 to 50 inches) of rain per year, but that rain is packed into a wet season lasting about six to eight months, followed by a long, dry stretch. This cycle of flood and drought is central to how savannas work.
Climate and Seasons
Tropical savannas, the most widespread type, stay warm year-round and receive between 76 and 100 centimeters of rain annually. A pronounced wet season alternates with a long dry season, and this rhythm shapes everything from plant structure to animal behavior. Grasses explode with growth during the rains, then go brown and dormant when the water stops.
Temperate grasslands sometimes overlap with savanna characteristics but tend to have more extreme temperature swings, with summers above 38°C and winters that can plunge to negative 40°C. Their rainfall is lower, typically 30 to 50 centimeters a year, falling mostly in late spring and early summer. These harsh winters and dry summers are what keep trees from taking over.
Why Fire Is Essential
Fire is not a disaster in a savanna. It is one of the forces that keeps the ecosystem alive. Natural and human-set fires have expanded grassy landscapes at the expense of forests for thousands of years. Without regular burning, shrubs and young trees would eventually crowd out the grasses and convert the landscape into woodland or forest.
The process works like this: during the dry season, dead grass becomes fuel. When fire sweeps through, it kills saplings and shrubs with thin bark but leaves mature trees standing, their thick bark and elevated canopies protecting them. Grasses, meanwhile, regrow quickly from their deep root systems once the rains return. The result is a landscape that resets itself, maintaining that signature open, tree-studded appearance.
Grazing pressure matters too. When large herbivores eat down the grass, fires burn cooler and shorter, which allows shrubs to survive and spread. When grazers are removed, grass accumulates, fires burn hotter, and even large trees can be killed. It is the balance between fire frequency and grazing that determines whether a savanna stays open or shifts toward dense bush.
How Plants Survive Drought and Fire
Savanna plants have evolved remarkable strategies for dealing with months without rain and regular burning. Many grasses and shrubs grow deep root systems that reach water far below the surface. Those same roots survive fires unharmed, allowing the plant to resprout even after everything aboveground has been scorched. Grasses can go completely dormant during dry spells and then grow rapidly once the rains arrive.
Trees have their own tricks. The baobab, one of the savanna’s most iconic species, grows up to 30 meters tall and stores water inside its massive trunk, drawing on that reserve to survive the dry season. Its thick, corky bark resists fire and slows water loss through evaporation. Acacia trees take a different approach to survival: when a grazer starts eating their leaves, they flood the foliage with bitter-tasting chemicals within minutes, limiting how much any one animal can consume. They also release airborne signals that prompt nearby acacias to do the same. One species, the whistling thorn acacia, hosts four species of aggressive ants that live inside its swollen thorns and swarm out to sting any animal that tries to browse.
Other plants store water underground in bulbs or swollen stems called corms. Many flower only during part of the year to conserve moisture, and some develop thick coverings or spines to deter animals from eating them.
Wildlife of the Savanna
Savannas harbor most of the world’s large mammal diversity. The open landscape and abundant grass support enormous populations of herbivores, from wildebeest and zebra to elephants and giraffes. These animals are not just residents of the savanna; they actively shape it. Elephants, which can weigh over 1,000 kilograms, are considered ecological engineers capable of altering vegetation on a landscape scale. They knock down trees, strip bark, and open up dense thickets, maintaining the mosaic of grass and woodland that other species depend on.
Large carnivores, including lions, leopards, and hyenas, regulate herbivore populations both by killing prey and by creating what ecologists call “landscapes of fear.” Herbivores avoid areas where predators are likely to ambush them, which means certain patches of vegetation get heavy grazing while others are left alone. This uneven pressure creates the patchy, varied habitat that supports so many different species.
This rich web of large animals is a relatively recent inheritance. During the Late Pleistocene, savannas supported at least 50 species of land animals weighing over 1,000 kilograms, including multiple species of elephants, rhinoceroses, and giant sloths in the Americas. Most of those giants are gone now, lost to extinction over the past tens of thousands of years. Africa retains the greatest concentration of surviving large mammals, which is one reason its savannas look so different from those on other continents.
Savanna Soils
The soils beneath savannas tend to be nutrient-poor, a consequence of prolonged weathering over millions of years. Phosphorus is often in short supply, and the soil is frequently acidic with high aluminum concentrations that lock up what little phosphorus exists. Regular dry-season fires make things worse by releasing nitrogen and sulfur into the smoke, removing those nutrients from the system entirely.
Savanna soils are often brownish and clay-rich. In Africa, landscapes commonly feature a predictable sequence from hilltop to valley: sandy, leached soils on the ridges give way to finer-grained soils on slopes, and deep, dark clays collect in the valleys. These valley clays, rich in a mineral called montmorillonite, crack open when dry and become extremely sticky when wet, sometimes trapping vehicles during the rainy season. In South America’s llanos, soils are generally young and better-drained but still tend to be low in nutrients.
Human Pressures on Savannas
Land-use change is one of the greatest threats to savanna ecosystems today, and tropical savannas are expected to be disproportionately affected in the coming decades. Agriculture, livestock grazing, and fuel-wood harvesting are the primary drivers. In southern Africa, communal lands and intensive farming surrounding remnant savannas are dramatically reducing the number of large trees, which provide critical ecological functions like shade, food for wildlife, and soil stabilization. Knobthorn trees, for example, are being drastically thinned by harvesting for fuel wood in areas adjacent to human settlements.
Rising atmospheric carbon dioxide is adding another layer of change. Higher CO2 levels can favor woody plants over grasses, potentially pushing savannas toward denser tree and shrub cover in a process called woody thickening. This shift could fundamentally alter the character of savanna landscapes, reducing the open grassland that supports grazing animals and the fire cycles that maintain the ecosystem’s balance.