September 20, 2010

Amazon Rainforest Resiliency

Filed under: Adaptation, Plants

Do a search on “Global Warming and Amazon Rainforest” and enjoy over 200,000 sites mostly proclaiming that “Amazon rainforest may become a desert” or “large portion of the rainforest will be lost” or you name it. Throw in the 200 indigenous cultures in the forest, add in some clever phrases like “lungs of the planet,” argue that the rainforest is being destroyed faster than anyone expected, and then claim “incalculable damages” all because of global warming. The cure for everything and anything is surely hidden in the rainforest of the Amazon, and the loss of that ecosystem could spell the end of us all.

Three recent papers appearing in leading scientific journals spell trouble for the alarmists’ claims about global warming and the precious and delicate Amazon rainforest.

The first paper appeared in Science magazine and was written by four scientists from the University of Arizona and Brazil’s University of São Paulo. Saleska et al. begin reminding us that “Large-scale numerical models that simulate the interactions between changing global climate and terrestrial vegetation predict substantial carbon loss from tropical ecosystems, including the drought-induced collapse of the Amazon forest and conversion to savanna.” They further explain that “Model-simulated forest collapse is a consequence not only of climate change–induced drought but also of amplification by the physiological response of the forest: Water-limited vegetation responds promptly to initial drought by reducing transpiration (and photosynthesis), which in turn exacerbates the drought by interrupting the supply of water that would otherwise contribute to the recycled component of precipitation. This physiological feedback mechanism should be observable as short-term reductions in transpiration and photosynthesis in response to drought under current climates.”

In 2005, Mother Nature conducted an experiment for us by producing a substantial drought in the Amazon; the drought peaked in intensity during July to September of that year with the hardest hit part of the Amazon occurring in the central and southwestern portions of Amazonia. Saleska et al. used satellite-based measurements and much to their surprise, they found that forest canopy “greenness” over the drought-stricken areas increased at a highly significant rate. They conclude that “These observations suggest that intact Amazon forests may be more resilient than many ecosystem models assume, at least in response to short-term climatic anomalies.”

Next up is an article in a recent issue of the Journal of Vegetation Science by seven scientists from Panama, Brazil, and California; the piece is entitled “Long-term variation in Amazon forest dynamics” and therefore must contain horrible news about the state of the rainforest, right? Wrong! Laurance and her team conducted five different surveys of the forest in a protected area 50 miles north of Manaus in the central Amazon; they made these measurements between 1981 and 2003. Getting right to the bottom line, they report that “Forest biomass also increased over time, with the basal area of trees in our plots, which correlate strongly with tree biomass, rising by 4% on average.” They then add “The suite of changes we observed—accelerating tree growth and forest dynamism, and rising biomass—largely accords with findings from other long-term, comparative studies of forest dynamics across the Amazon Basin.” They state “One of the most frequent explanations for such findings is that forest productivity is rising, possibly in response to increasing CO2 fertilization or some other regional or global driver(s), such as increasing irradiance or rainfall variability.” We are partial to the increasing CO2 explanation, and it is worth noting that the first sentence in the “Conclusions” section in their abstract clearly states “The increasing forest dynamics, growth, and basal area observed are broadly consistent with the CO2 fertilization hypothesis.”

Our third recent article was written by three scientists from Brazil and Germany and it appeared in Global Biogeochemical Cycles. Lapola et al. begin noting that “Tropical South America vegetation cover projections for the end of the century differ considerably depending on climate scenario and also on how physiological processes are considered in vegetation models.” To investigate the future of the vegetation of the Amazon, the team created a numerical “Potential Vegetation Model” that could be coupled with global climate models. As seen in their figure below (Figure 1), the vegetation model appears to accurately replicate the current vegetation in the region. When they simulated climate change in the future and they included the CO2 fertilization effect, the vegetation was largely unchanged. Without the CO2 fertilization effect, the rainforest all but disappears under their expected change in climate. And if the climate does not change much and the CO2 fertilization effect is realized, the rainforest expands considerably.

In their own words, Lapola et al. conclude “Biome projections for the end of the century in tropical South America are quite variable, depending not only on the climate scenario, but also on the effect of CO2 fertilization on photosynthesis.” Furthermore “Our simulations show that if, in the future, CO2 fertilization effect does not play any role in tropical ecosystems then there must be substantial biome shifts in the region, including substitution of the Amazonian forest by savanna.” If the CO2 fertilization does in fact occur (and 1,000s of experiments suggest it is occurring and will occur in the future), “most of Amazonia would remain the same.”


Figure 1. (a) Natural vegetation reference map; (b) potential vegetation simulated by the Potential Vegetation Model under 1961–1990 climate; (c) predicted vegetation with climate change and CO2 fertilization; (d) predicted vegetation with climate change and no CO2 fertilization (white grid points denote nonconsensus); and (e) 1961–1990 climate and atmospheric CO2 of 730 ppm (from Lapola et al., 2009).

These three as well as many other recent articles lead us to the conclusion that the Amazon rainforest is doing fine when it comes to the climate, and it will probably be even better off in the future thanks to elevated levels of atmospheric CO2. Alarmists’ claims to the contrary are not supported by observations in the forest or the modeling studies that include the effects of higher levels of CO2.

References:

Lapola, D.M., M.D. Oyama, and C.A. Nobre. 2009. Exploring the range of climate biome projections for tropical South America: The role of CO2 fertilization and seasonality. Global Biogeochemical Cycles, 23, GB3003, doi:10.1029/2008GB003357.

Laurance, S.G.W., W.F. Laurance, H.E.M. Nascimento, A. Andrade, P.M. Fearnside, E.R.G. Rebello, and R. Condit. 2009. Long-term variation in Amazon forest dynamics. Journal of Vegetation Science, 20, 323–333.

Saleska, S.R., K. Didan, A.R. Huete, H.R. da Rocha. 2007. Amazon forests green-up during 2005 drought. Science, 318, 612.




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