August 25, 2010

Amazon tolerates extreme weather

A recent study, published in the Proceedings of the National Academy of Sciences, suggests that the relatively undisturbed areas of the Amazon rainforest may be more tolerant of seasonal droughts than previously thought.

“Many scientists predict that droughts will become more common in the Amazon as global warming continues to rise, so the forest’s response is an issue of critical importance to conservationists and anyone trying to mitigate climate change by maintaining forest carbon stocks”, suggests Matthew Owen of Cool Earth Action.

In 2005, the Amazon experienced a “once in a lifetime” drought when rainfall was reduced by up to 75% in some areas. Once again, in 2010, the Amazon is experiencing low river levels because of an unusually dry “dry season” in the river’s headwaters located along the western edge of the Amazon Basin.

“Data gathered by NASA’s Terra satellite shows that the canopy of the Amazon rainforest actually grew and turned greener during and after the 2005 drought”, says Owen.

The explanation may well lie in a combination of factors. Cloud cover is less during drought, enabling more sunlight to reach the forest for photosynthesis; but, the forest also responds to rising levels of atmospheric carbon dioxide. More readily available carbon dioxide helps trees grow faster, absorb more carbon and also reduce water loss during photosynthesis.

Taken together, these factors may help improve forest resilience to drought. Other studies suggest that the availability of nutrients such as nitrogen may be a limiting factor to this general resilience.



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