UA study shows rain forest resilient in drought

2007-09-20T00:00:00Z UA study shows rain forest resilient in droughtBy Dan Sorenson Arizona Daily Star Arizona Daily Star
September 20, 2007 12:00 am  • 

It doesn’t sound right, but the Amazon jungle responded to a 2005 drought by turning greener rather than brown, and a University of Arizona-led study of the surprise may lead to a reworking of gloomy forecasts for the world’s largest rain forest.

Rain forest trees, it would seem, used water picked up by deep roots and the added sunlight of cloudless drought skies to turn up the photosynthesis, according to Scott Saleska, a UA assistant professor of ecology and evolutionary biology.

Saleska is the lead author on the piece just published in the online version of the American Association for the Advancement of Science’s Journal “Science.”

Using images from NASA’s Terra satellite, Saleska said the team looked at the changes in the rain forest canopy during the 2005 drought.

The group was made up of Saleska and the UA’s Kamel Didan and Alfredo Huete, along with Humberto R. da Rocha, of the University of Sao Paulo, Brazil. Didan is an associate research scientist in soil, water and environmental science. Huete is a professor of soil, water and environmental science. Da Rocha is in the Brazilian university’s Department of Atmospheric Science.

“If you anthropomorphize a little bit,” Saleska said, “these trees are not dumb. They’ve been living here tens of millions of years. If you’re designing trees to live, make sure that they could survive. Make them take advantage of that sunlight.”

He said modeling of the rain forest’s reaction to drought has been based mostly on what is known about temperate forests.

Still, he said, it doesn’t mean global climate change won’t affect the rain forest.

“You take away enough water for a long enough time, the trees are going to die,” says Saleska.

The good news is that the trees are, at least temporarily, able to survive — even thrive — during short periods of drought.

The research will likely force a reworking of computer models that predict global warming-induced drought will kill the world’s largest rain forest by the middle of the century and turn it into savannah, according to UA global climate modeler Joellen Russell, a UA assistant professor of geosciences.

“This is a great piece of work,” Russell said, because the huge rain forest has implications for the entire planet’s health.

In particular, she said the predictions that global warming-induced drought would turn the forest into grasslands has far-reaching impacts because of all the carbon that would be released into the atmosphere if the huge biomass were to die and decompose.

“It’s just one piece of the climate system, but it’s an important one,” Russell said of the Amazon rain forest.

Saleska says the work is not done, that more needs to be learned about exactly what is going on with the trees, soil, groundwater and atmosphere at ground level during fluctuations in rainfall.

He hopes to answer questions about drought reaction using a five-year, $2.5 million National Science Foundation grant.

The study will look at the amount of water available to trees, and use instruments mounted in towers to measure the carbon dioxide, water vapor and determine whether trees are growing or dying over longer periods.

Related work will be done at the UA’s recently acquired Biosphere 2, the 3-acre, glass-enclosed habitat near Oracle.

Contact reporter Dan Sorenson at 573-4185 or

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