A savannah is a tropical or subtropical grassland with scattered trees, defined by distinct wet and dry seasons and warm temperatures year-round. Savannahs cover roughly one-fifth of Earth’s land surface, making them one of the planet’s most widespread biomes. They exist on every continent except Antarctica, with the largest stretches found across sub-Saharan Africa, central Brazil, and northern Australia.
Climate That Shapes the Landscape
Savannahs are defined more by their warm climate than by their vegetation. Temperatures rarely drop below 60°F (15°C), and for most of the year daytime highs range between 80 and 100°F (27 to 37°C). What truly sets savannahs apart from other grasslands is the sharp division between a wet season and a dry season, each lasting roughly six months.
During the wet season, a savannah can receive anywhere from 20 to 50 inches (500 to 1,200 mm) of rain. During the dry season, that number drops to about 4 inches (100 mm) or less, and months may pass with no rainfall at all. This cycle of flood and drought is the engine behind everything else in the ecosystem: which plants survive, where animals travel, and how the soil develops.
Where Savannahs Are Found
Africa holds the most iconic savannahs, stretching across East Africa’s Serengeti and Masai Mara, down through southern Africa’s Kruger region, and across the vast Sahel belt south of the Sahara. In South America, Brazil’s cerrado is the world’s most biodiverse savannah, covering an area larger than Alaska. Australia’s tropical savannahs blanket much of the continent’s northern coast. Smaller pockets also exist in India and Southeast Asia, wherever seasonal rainfall and warm temperatures create the right conditions.
What Grows There
The classic savannah look, tall grass dotted with widely spaced trees, is a product of water scarcity. Trees can’t grow close together because there isn’t enough moisture to support dense forest canopy. The grasses that dominate the ground layer use a specialized form of photosynthesis (called C4) that lets them thrive in hot, dry conditions and grow rapidly when the rains arrive. These grasses are also highly flammable once they dry out, which plays a critical role in keeping the ecosystem open.
Savannah soils vary widely. In parts of southern Africa, for example, nutrient-poor sandy soils support broad-leafed trees, while richer clay-based soils in drier zones support fine-leafed species like acacias. Trees that do grow in savannahs tend to concentrate carbon and nitrogen in the soil beneath their canopies, creating small patches of enriched ground. This uneven distribution of nutrients helps explain why savannah vegetation looks patchy rather than uniform.
The Role of Fire
Fire is not a disaster in a savannah. It’s a maintenance tool. Lightning strikes during the transition between dry and wet seasons regularly ignite the dead grass layer, and these burns prevent the landscape from slowly converting into woodland or forest. Research in temperate oak savannahs in Minnesota found that burning at least three times per decade prevented new tree saplings from filling in the canopy. When fires occurred fewer than twice per decade, dense thickets of young trees took over, and the open grassland character disappeared.
Fires also recycle nutrients locked in dead plant material back into the soil, and the fresh green regrowth that follows a burn is nutritionally rich. Smaller herbivores in African savannahs are strongly drawn to recently burned patches for exactly this reason, taking advantage of the tender, high-quality forage.
Animals and the Food Web
African savannahs support the most diverse large-mammal communities left on Earth, and the interactions between those animals shape the landscape as much as climate and fire do. The food web has a clear structure: a grassy base, a large and varied group of herbivores, and a predator community topped by lions.
Body size determines how herbivores use the landscape. Mega-herbivores like elephants and giraffes are too large for most predators to threaten, so they roam widely through woodlands and along rivers, tolerating lower-quality food. Mid-sized migratory species like wildebeest and zebra follow the rains across vast distances, tracking seasonal flushes of grass. Smaller, resident species like impala and steenbok stick to compact territories where forage quality is consistently high, relying on cover and vigilance to avoid predators.
Lions tend to associate positively with migratory herds, following their movements, while smaller resident herbivores often avoid the same areas. This predator-prey dynamic spreads grazing pressure across the landscape rather than concentrating it, which helps prevent overgrazing in any single area. When top predators disappear from a savannah, the cascading effects can dramatically reshape vegetation structure and species distribution.
Water as a Seasonal Resource
Water availability shifts dramatically between seasons, and animals have adapted their movement patterns accordingly. During the wet season, temporary pools and seasonal streams appear across the landscape, allowing animals to spread out. As the dry season progresses, those ephemeral sources dry up and animals contract toward permanent water, like rivers and large waterholes.
A study tracking savannah elephants in Botswana’s Okavango region found that their daily distance to the nearest temporary water source increased significantly during the dry season, as those sources disappeared and the elephants shifted toward permanent rivers. This seasonal compression around water creates intense competition and concentrates predator-prey encounters, making the dry season the most ecologically dramatic period of the year.
Why Savannahs Matter
Savannahs store enormous amounts of carbon in their soils and root systems, often more below ground than above. Because grasses regrow quickly after fire or grazing, savannahs cycle carbon rapidly, making them important players in the global climate system. They also support the livelihoods of hundreds of millions of people through cattle grazing, agriculture, and tourism.
The biggest threats to savannahs today are conversion to cropland, disruption of natural fire cycles, and climate shifts that alter rainfall timing. When fires are suppressed, trees gradually encroach and the grassland disappears. When rainfall patterns shift, the delicate balance between grass and woodland tips in one direction or the other. The savannah’s open, sun-drenched simplicity is deceptive; it’s maintained by a precise set of interacting forces that are surprisingly easy to disrupt.