Small trees offer hope for rainforests

Small trees that grow up in drought conditions could form the basis of more drought-resistant rainforests, says new research. Severe and long-lasting droughts are becoming more common in the Amazon, often killing large trees that form the forest canopy.

A new study led by the University of Exeter suggests small trees adapt better to droughts and could grow into a new generation to help the rainforest survive.

Using data from a long-running drought experiment in Brazil, the scientists discovered small trees respond positively to the extra light they get when larger trees die, managing to increase their capacity for photosynthesis and their growth despite the lack of water.

“Conditions in the Amazon are shifting due to climate change, and trees will have to adapt if they are to survive,” said lead author David Bartholomew in a statement. “Our findings show that small trees are more capable of changing their physiology in response to environmental changes than their larger neighbours.”

He added that having grown in up in drought conditions, “these trees might develop traits that will help them cope with future droughts – even once they are fully grown.”

The study examined trees in a 15-year Amazonian drought experiment, in which clear plastic panels catch 50per cent of rainfall. Researchers sampled 66 small trees (1-10 cm diameter at a height of 1.3m from the ground) and 61 large trees (more than 20cm in diameter) in the drought experiment area and a nearby control area with no rainfall exclusion.

Small trees in the drought area showed increased capacity for photosynthesis (Jmax 71%, Vcmax 29%), 32% more leaf respiration and 15% more leaf mass per area compared to small trees in the control area.

The responses of tree species in the study varied, with some showing a strong ability to adapt and some showing very little. More research is needed to understand how this might change the makeup of the famously diverse Amazon rainforest in the future.

Photo credit: Flickr Creative Commons

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