From: ScienceDaily
Published June 29, 2012 06:43 AM

Africa's Savannas May Become Forests

A new study published today in Nature by authors from the Biodiversity and Climate Research Centre and the Goethe University Frankfurt suggests that large parts of Africa's savannas may well be forests by 2100. The study suggests that fertilization by atmospheric carbon dioxide is forcing increases in tree cover throughout Africa. A switch from savanna to forest occurs once a critical threshold of CO2 concentration is exceeded, yet each site has its own critical threshold. The implication is that each savanna will switch at different points in time, thereby reducing the risk that a synchronous shock to the earth system will emanate from savannas.

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Tropical grasslands, savannas and forests, areas the authors call the savanna complex, are expected to respond sensitively to climate and atmospheric changes. This is because the main players, grasses and trees, differ fundamentally in their response to temperature, carbon dioxide supply and fire and are in an unrelenting struggle for the dominance of the savanna complex. The outcome of this struggle determines whether vast portions of the globe’s tropical and sub-tropical regions are covered with grasslands, savannas or forests. In the past such shifts in dominance have played out in slow motion, but the current wave of atmospheric changes has accelerated the potential rate of change. 

Experimental studies have generally shown that plants do not show a large response to CO2 fertilization.  "However, most of these studies were conducted in northern ecosystems or on commercially important species" explains Steven Higgins, lead author of the study from the Biodiodversity and Climate Reseach Centre and Goethe-University. "In fact, only one experimental study has investigated how savanna plants will respond to changing CO2 concentrations and this study showed that savanna trees were essentially CO2 starved under pre-industrial CO2 concentrations, and that their growth really starts taking off at the CO2 concentrations we are currently experiencing."

African Savannah via Shutterstock.

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