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How did cooler climates and reduced rainfall help savannas spread during the Miocene Epoch?
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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.
During the Miocene Epoch, global climates became progressively cooler, which played a critical role in the expansion of savannas.
The cooling of ocean surface temperatures reduced the rate of water evaporation, which in turn slowed the global hydrologic cycle. This reduction in the cycle led to decreased cloud formation and precipitation. As rainfall lessened, particularly in the edges of the tropics, the environment shifted toward more seasonally dry conditions. These changes significantly affected the vegetation of midlatitude regions, allowing grasses—the dominant plants of the savanna—to thrive and spread into these newly created habitats.1