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How does grazing change the balance between woody plants and grasses 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 a savanna, grazing animals can shift the balance between woody plants and grasses in either direction, depending on their specific feeding habits and population levels.1
- Shifting toward woody plants: When grass-eating mammals overgraze an area, they can push grasses toward local extinction. Because the upper branches of many woody plants are out of reach for these herbivores, the trees and shrubs are not consumed. This allows them to regenerate and become denser, potentially transforming the landscape from a savanna into a forest.1
- Shifting toward grasses: Conversely, if populations of herbivores that consume woody vegetation increase, they can destroy trees and shrubs, effectively converting a wooded savanna into a grass-dominated landscape.1
It is important to note that overgrazing by livestock is a significant threat to these ecosystems. Beyond altering plant composition, it can lead to soil compaction, erosion, and desertification, which degrades the overall health of the rangeland. Sustainable management, such as rotational grazing, is essential to prevent the depletion of native grasses and maintain the ecological balance.23