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How do savannas form transition zones between rainforests and deserts?

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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.

Savannas function as geographic and environmental transition zones because they exist along a continuum between the rainforests of equatorial regions and the deserts of higher latitudes.1

This transition is primarily driven by gradients in precipitation and seasonal moisture availability. While rainforests receive high, year-round rainfall, savannas are characterized by alternating wet and dry seasons. As one moves away from the equatorial belt toward the subtropics, the duration of the dry season increases, leading to a gradual shift in vegetation.12

In these regions, the climate becomes too dry to support the closed-canopy structure of a rainforest, yet it remains sufficiently moist to prevent the extreme aridity of a desert. The resulting savanna ecosystem is defined by a continuous grass cover with scattered trees and shrubs, a structure maintained by complex interactions between climate, soil conditions, grazing, and wildfire.1234