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Rising temperatures over the last few decades in Malaysia and Panama may have decelerated the growth of rainforest trees, according to a study.

This could significantly affect the ability of trees to store carbon dioxide, raising the atmospheric concentrations of this greenhouse gas, say the researchers.

The study is the result of 24 years worth of data on tree species from Barro Colorado Island in the Panama Canal and the Pasoh Forest Reserve southeast of Kuala Lumpur, Malaysia.

Lead author Kenneth Feeley, from the US-based Harvard University, presented the research last week (7 August) at the annual meeting of the Ecological Society of America in San Jose, California, United States. The study had been published previously in the June issue of the journal Ecology Letters.  

The researchers found that as many as 71 per cent of plant species in Panama and up to 95 per cent of species in Malaysia showed decreases in growth rates.

During this time, the daily minimum temperatures and cloudiness increased. For example, the minimum nightly temperature on Barro Colorado Island has increased by more than one degree Celsius over the last 20 years.

It is already known that increasing temperatures speed up the process of respiration in plants, causing them to release more carbon dioxide.

Feeley and his colleagues suspect that warmer temperatures also slow down the process of photosynthesis, during which plants take in carbon dioxide — although they emphasise that this is still a theory.

"We are only able to state that the slowing in growth that we observed is consistent with the hypothesis that increases in temperature will cause decreases in tree growth," explained one of the researchers, Joseph Wright, from the Smithsonian Tropical Research Institute in Panama.

If this is the case, in the future tropical forests could emit large amounts of carbon dioxide, write the researchers.

Wright told SciDev.Net that he hopes other researchers will now analyse other tropical regions with the same climate patterns as Malaysia and Panama.

Link to abstract in Ecology Letters

Reference: Ecology Letters 10, 461 (2007)