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The Surprising Role of CO2 in Changes on the African Savanna
Recent studies show that many of the world’s savannas, including famed southern African landscapes, are experiencing significant change as rising levels of carbon dioxide in the atmosphere favor the growth of trees over grasslands.
by Adam Welz
Africa’s savanna ecosystems — which include the thorn tree-studded plains of the Serengeti, the open woodlands of the Kruger National Park, and the dry, red sand savannas of the Kalahari — occupy about 70 percent of the continent south of the Sahara Desert. And evidence is mounting that these iconic and biodiverse landscapes are changing as rising levels of carbon dioxide in the atmosphere fuel the growth of trees at the expense of grasses, leading to an increasingly wooded landscape.
A 2012 survey of experimental plots in South African savannas — where fires, rainfall, and herbivore pressure have remained constant for decades — shows large increases in woody plant mass, which the authors primarily attribute to the so-called “CO2 fertilization effect,” the enhancement of plant growth caused by increasing atmospheric carbon dioxide. A modeling study published in the journal Nature last year describes a recent, rapid shift in extensive areas of African grassland and savanna to more densely vegetated, wooded states, a trend that is expected to accelerate in coming decades as atmospheric concentrations of CO2 rise. Already there are signs that open-country animals like the cheetah are suffering as savanna becomes more wooded.