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The Fate of Amazonian Forests in a CO2-Enriched and Warmer World
Lapola, D.M., Oyama, M.D. and Nobre, C.A. 2009. Exploring the range of climate biome projections for tropical South America: The role of CO2 fertilization and seasonality. Global Biogeochemical Cycles 23: 10.1029/2008GB003357.

Many are the studies that have evaluated the impacts of greenhouse-gas-induced global warming on forest dynamics in tropical South America, the results of which generally portend, in the words of the authors, "long-term replacement by drier biomes such as tropical savanna, C4 grasslands or even desert."

What was done
Lapola et al. expand this somewhat myopic view by using a potential vegetation model (CPTEC-PVM2) "to analyze biome distribution in tropical South America under a range of climate projections," while taking into consideration the aerial fertilization effect of atmospheric CO2 enrichment, as well as its transpiration-reducing effect.

What was learned
The Brazilian and German researchers say their modeling work reveals that "if the CO2 'fertilization effect' indeed takes place and is maintained in the long term in tropical forests, then it will avoid biome shifts in Amazonia in most of the climate scenarios, even if the effect of CO2 fertilization is halved [italics added]." In fact, they say that the CO2 fertilization effect, "when fully or half considered, overwhelms [italics added] the impacts arising from temperature (in agreement with Lloyd and Farquhar, 2008) and even some of the precipitation changes projected by most of the global climate models, resulting in higher net primary production by the end of the century."

What it means
Without the biological benefits provided by the ongoing rise in the air's CO2 content, Lapola et al. conclude "there must be substantial biome shifts in the region, including substitution of the Amazonian forest by savanna," but that with these benefits, "most of Amazonia would remain the same" as it is today.

Lloyd, J. and Farquhar, G.D. 2008. Effects of rising temperatures and [CO2] on the physiology of tropical forest trees. Philosophical Transactions of the Royal Society Series B 363: 1811-1817.

Reviewed 11 November 2009