The Surprising Role of CO2 in Changes on the African Savanna Africa¹s 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 ³CO2 fertilization effect,² 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. This trend is not confined to Africa. An Australian study released last month, which relied in part on satellite data, concludes that foliage cover in warm, arid areas worldwide has increased by about 11 percent in the last three decades due to higher CO2 levels. Randall Donohue and colleagues at the Australian national science agency, known as CSIRO, and the Australian National University said that the CO2 fertilization effect ³is now a significant land surface process² shaping ecosystems across large parts of the planet.
Posted on: Thu, 13 Jun 2013 23:55:48 +0000
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