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How does increasing rainfall affect the number of trees in a savanna?
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Savanna
A savanna marked with acacia trees in Serengeti National Park, Tanzania. Africa's Serengeti Plain is commonly used as an example of the savanna biome—a hot, seasonally dry ecological region characterized by an open tree canopy (i.e., scattered trees) above an understory of continuous grasses.
In the context of the savanna, the tree component generally becomes more significant as rainfall increases. Because trees require consistent access to water, higher precipitation levels can facilitate a shift in vegetation structure, potentially causing dry savannas to transition toward increased shrub and tree coverage. Under these conditions, a savanna may eventually transform into forest or scrubland.123
However, this relationship is complex and influenced by several other environmental factors. While rainfall is a primary driver, the density of trees is also shaped by:
- Soil characteristics: Factors such as depth, texture, and the ability to hold water influence whether an area can support a closed forest or remains an open savanna.13
- Fire regimes: Dry-season fires, which are fueled by grass, can kill young tree saplings and limit tree density. Increased tree cover can sometimes reduce the intensity of these fires, further favoring woody plant growth.13
- Grazing pressure: The presence of herbivores can either promote or reduce tree density depending on their feeding habits and population levels.3