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Study: Heavy Rainfall Favors Grass Over Trees

FILE - Lioness walks through the tall grass in the Phinda Private Game Reserve, near Hluhluwe, South Africa, April 2012.

Rain should be good for trees, scientists thought. But African savannas — rolling grasslands with heavy rainfalls and spells of drought — do not have many trees.

Princeton University researchers have an explanation: the way grasses absorb and use water gives them a competitive edge over trees.

In a study published in the Proceedings of the National Academy of Sciences, they point out grasses can quickly absorb water to support photosynthesis and rapid growth, but trees, with tougher leaves and roots, are not as efficient in taking advantage of abundant water.

Trees withstand droughts better than grasses, but in a future that is predicted to be warmer and much wetter, the authors predict even fewer trees on the savanna. That could be good for grazers and other herbivores, but worse for birds and other wildlife that depend on trees. It could also reduce the amount of CO2 pulled from the atmosphere.

The Princeton researchers developed a mathematical model to mimic how trees and grasses photosynthesize and absorb water, and factored in rainfall numbers from observations across the savanna to come up with their conclusions. First author Xiangtao Xu said the model could help communities make better policies and decisions to adapt to climate change.

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