The savanna is a grassland ecosystem characterized by expansive grassy plains interspersed with scattered trees and shrubs. This environment is found across tropical and subtropical regions on every continent except Antarctica.
The Savanna Environment
The savanna environment is shaped by distinct climatic patterns, primarily pronounced wet and dry seasons. Annual precipitation typically ranges from 50 to 150 centimeters, with the dry season often extending longer than the wet period. Temperatures remain consistently warm to hot throughout the year, usually fluctuating between 20°C and 30°C (68°F and 86°F).
Frequent wildfires are a natural and integral component of savanna ecosystems. These fires, often ignited by lightning during the dry season, are fueled by the abundant dry grasses. They play a significant role in preventing dense forest growth, thus maintaining the open, grassy landscape. The soils in savannas are generally low in fertility, often being sandy or loamy with a thin layer of humus.
How Savanna Trees Survive
Trees in the savanna have developed specific features to endure the harsh conditions, particularly prolonged dry periods and frequent fires. Many species possess extensive root systems that can reach deep underground water sources, allowing them to access moisture even when surface soils are dry.
Another common adaptation is thick, fire-resistant bark, which protects the tree’s inner tissues from the intense heat of savanna fires. This protective layer enables trees to survive burns and regenerate. Many savanna trees are also deciduous, shedding their leaves during the dry season to minimize water loss.
Some savanna trees feature small leaves or thorns to reduce water evaporation from their surface. Certain species, like the baobab, store large volumes of water in their swollen trunks, providing essential hydration during extended droughts.
Identifying Savanna Trees
Various iconic tree species have adapted to thrive across the world’s savannas. The Baobab tree ( Adansonia digitata ) is prominent in African and Australian savannas, recognized by its massive, often bottle-shaped trunk that stores water. These long-lived trees can reach thousands of years old.
Acacia species, including Vachellia and Senegalia, are widespread in African savannas, known for their flat-topped canopies and protective thorns. These trees often have deep taproots to reach groundwater, and some exhibit chemical defenses against herbivores. In Southern Africa, the Mopane tree ( Colophospermum mopane ) is identifiable by its distinctive butterfly-shaped leaves and its prevalence in hot, low-lying areas. Mopane wood is dense and resistant to termites, making it valuable for construction.
The Marula tree ( Sclerocarya birrea ) is another notable species in Southern African savannas, valued for its nutritious, vitamin C-rich fruit. This deciduous tree sheds its leaves during the dry season and is resilient to drought. In Australian savannas, Eucalyptus species are dominant, characterized by their evergreen nature and adaptations to fire.