Droughts slow Amazon carbon uptake

Study shows rainforest resilience

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How much drought can the Amazon withstand? Photo courtesy NASA Earth Observatory.

Staff Report

After studying the impacts of recent droughts in the Amazon, researchers are warning that the rainforest may gradually be losing its ability to remove carbon from the atmosphere. But their study also shows that the ecosystem is resilient and can recover quickly in between droughts.

The study used data from from droughts in 2005 and 2010, finding that tree growth slowed across the vast forests of the Amazon Basin. Long-term measurements from theRAINFOR network spanning nearly a hundred locations across the Amazon Basin helped show how the rainforest temporarily lost biomass. Both droughts killed many trees, but the 2010 drought also had the effect of slowing the growth rates of the survivors, suggesting that many trees were adversely affected but not to the point of death.

“The first large-scale, direct demonstration of tropical drought slowing tree growth is extremely important,” said lead author Dr Ted Feldpausch, senior lecturer in Geography at the University of Exeter. “It tells us that climate changes not only increases the rate of loss of carbon dioxide to the atmosphere, by killing trees, but also slow down the rate of uptake. And yet, the Amazon clearly has resilience, because in the years between the droughts the whole system returned to being a carbon sink, with growth outstripping mortality.”

As the most extensive tropical forest on Earth, the Amazon forest stores 100 billion tonnes of carbon in biomass, so changes here have global consequences. The research provides important new understanding of the impact of climatic change on the behaviour of forests and CO2 levels.

“For more than 20 years the Amazon has been providing a tremendous service, taking up hundreds of millions more tonnes of carbon every year in tree growth than it loses through tree death. But both the 2005 and 2010 droughts eliminated those net gains,” said Co-author Professor Oliver Phillips, from the University of Leeds.

The research represents a large step forward in understanding how forests respond to repeated natural droughts at the scale of the Amazon. However, the researchers caution there is still much to learn. Not only have droughts recurred more frequently, but temperatures in Amazonia are on the rise, and a greater understanding of the effect of the interaction between the two is needed.

Professor Phillips added: “These climate changes are also affecting the exceptional plant and animal diversity of Amazonia. A big challenge now is to discover which species are at risk.”

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