The effects of the 2005 drought have been debated since 2007, when researchers reported in Science that photosynthesis within the canopy had increased, leading the Amazon basin to ‘green up’ during the dry period. But in 2010 another group reported that they were unable to reproduce the results using the same data3.
“The ‘green-up’ is a short-term response and a bit of a red herring,” says Oliver Phillips, a tropical ecologist at the University of Leeds, UK. But the latest study “transcends that debate”, he says. “The question of the underlying health of the forest is much deeper than the instantaneous response.”
A drawback of the method used in the earlier studies — which used satellite measurements to estimate forest greenness using reflected solar radiation — is that the data can be muddied by clouds and atmospheric aerosols. So for the latest study, Sassan Saatchi, a remote-sensing expert at the California Institute of Technology Jet Propulsion Laboratory in Pasadena, California, studied the forest’s microwave ‘silhouette’, showing its contours instead of its greenness. To look at canopy structure, he and his colleagues used microwave satellite data, which are unaffected by clouds, from a NASA probe. When it passed over lush canopy, the satellite sensor recorded a smooth signal. Bare branches, thinned leaves and missing trees showed more roughness.
The researchers found that more than 70 million hectares of rainforest in the western Amazon — an area nearly twice the size of California — were hit by the drought. And the canopy’s recovery dragged on long after the drought ended, with its biomass and fullness still below pre-drought levels in 2009 when the satellite suffered a mechanical failure. In 2010, an even stronger drought hit a larger swathe of the Amazon....
Aerial view of the Amazon, shot by lubasi, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license
No comments:
Post a Comment