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Why do protected areas of African savanna sometimes grow back into deciduous forest?

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Flat savanna plain with scattered acacia trees under a partly cloudy sky in Serengeti National Park, Tanzania. — 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.

Protected areas of African savanna often revert to deciduous forest when they are shielded from wildfire and grazing pressure.1

In a typical savanna ecosystem, fire acts as a critical disturbance that consumes grasses and leaf litter, which helps maintain the open landscape by killing or suppressing young, fire-sensitive woody plants. When these areas are protected from burning, the natural suppression of woody vegetation is removed, allowing trees and shrubs to regenerate and become denser.123

This transition is further influenced by the absence of large herbivores that would otherwise browse on woody plants. Without the combined impact of fire and grazing to keep the woody component in check, the vegetation profile shifts from an open, grass-dominated savanna toward a closed-canopy deciduous forest. This process demonstrates that the savanna is a dynamic environment whose structure is heavily dependent on ongoing disturbances.132