The savanna is a woodland-grassland biome found across Africa, Australia, South America, and India, covering approximately 20% of Earth’s land surface. This environment is characterized by consistently warm temperatures and a distinct seasonality of precipitation, featuring a long dry season followed by a wet season. The landscape’s defining feature is an open canopy, where trees are sufficiently scattered to allow sunlight to reach the ground below. This structure supports an unbroken layer of non-woody plants, distinguishing the savanna from denser forests and arid deserts.
The Foundation: Grasses and Herbaceous Plants
The flora of the savanna is dominated by grasses, which form the primary layer of vegetation beneath the scattered trees. These grasses are typically coarse and grow in dense tufts or patches, with areas of bare ground visible between them.
Many savanna grasses are perennial, allowing them to survive the annual dry season and regenerate quickly when the rains return. Species like Rhodes grass, red oat grass (Themeda triandra), star grass, and lemon grass are common across different savanna regions. In wetter savanna areas, giant grasses such as elephant grass (Pennisetum purpureum) can grow impressively tall, sometimes reaching heights of up to 10 feet.
The ground layer also includes various herbaceous plants, often called forbs, which grow interspersed among the grasses. These non-grass flowering plants contribute to the overall biodiversity of the understory. In Australian savannas, species like kangaroo grass (Themeda) and the prickly spinifex grasses (Plectrachne) are prominent.
Woody Plants: Trees and Shrubs
While grasses dominate the ground, the savanna is also home to a variety of woody plants, including trees and shrubs. These trees often feature a distinctive umbrella-shaped canopy, which maximizes the exposure of their small leaves to solar radiation while minimizing water loss through transpiration. Their wide spacing is primarily attributed to the limited seasonal rainfall.
The Acacia species are the most iconic trees of the African savanna, recognized by their flat-topped crowns and long, sharp thorns. Examples include the Umbrella Thorn Acacia (Acacia tortilis) and the Whistling Thorn (Vachellia drepanolobium). The Baobab (Adansonia genus) is another savanna tree, known for its massive, bulbous trunk that gives it an “upside-down” appearance.
Other notable woody species include the Combretum (bushwillows) and Brachystegia trees, which form the dense canopy of the Miombo woodlands found in central and southern African savannas. Succulent trees, such as the Candelabra Tree (Euphorbia candelabrum), are also present. Shrub species like the raisin bush and buffalo thorn contribute to the lower woody layer, especially in drier regions.
Survival Strategies: Adaptations to Fire and Drought
Savanna plants have evolved specialized mechanisms to endure the two major environmental pressures: drought and frequent wildfires. A primary strategy for drought survival is the development of deep taproot systems. These roots can penetrate the soil, allowing plants, such as the Acacia, to access deep groundwater reserves during the dry season.
Many plants employ xerophytic adaptations to conserve water. This includes shedding leaves during the dry period, like the Baobab and Miombo trees, to minimize water loss through transpiration. The Baobab tree further utilizes its immense trunk to store large volumes of water, which it draws upon during the arid months. Some grasses and trees also develop waxy or small leaves to reduce surface area for evaporation.
Adaptations to fire, known as pyriscence, are important for survival in this fire-prone ecosystem. Trees like the Baobab and certain Acacias possess thick, corky bark that acts as an insulator, protecting the living tissue beneath from the heat of fast-moving grass fires. Grasses survive due to underground storage organs like rhizomes or bulbs, which contain the plant’s growth tissues. These protected organs allow for rapid regrowth of the grass shoot shortly after a fire has passed, quickly utilizing the nutrient-rich ash left behind.