Small Drought-Resilient Trees May be the Future of the Amazon Rainforest

According to a new study, small trees growing in conditions of drought may be the future of an Amazon rainforest that is drought-resistant.

Severe Droughts Are Becoming More Common

The Amazon rainforest has been experiencing prolonged and severe droughts more and more. These droughts usually kill the large canopy trees of the forest.

A new study by the University of Exeter researchers has found that small trees may better adapt to these droughts and possibly help sustain the rainforest. The study was published in Plant, Cell, and Environment.

The scientists used the data of a Brazilian long-term drought experiment. They discovered that small trees positively respond to additional light that they receive when larger, higher trees disappear. It increases their capacity to photosynthesize and enables them to grow better despite less water being available.

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Global Systems Institute, University of Exeter NERC GW4+ DTP or Doctoral Training Partnership Ph.D. student and lead study author David Bartholomew says that rainforest conditions are changing as global warming progresses. Because of these shifting conditions, trees must adapt to the changes for them to survive.

According to Bartholomew, the long-term experiment showed that large trees are vulnerable to drought conditions, and most probably will not survive if the droughts are prolonged, increase their severity, and occur more often.

Before, little was known regarding small trees' responses in the understorey that could be critical in ensuring that tropical rainforests have a future. The understorey area of a rainforest is often humid and dark. Since the trees found here are always in conditions of lower light, they typically downgrade their capability to photosynthesize to conserve more resources.

Study Methodology

Bartholomew's research team examined the trees from the fifteen-year drought experiment. In it, the researchers used panels of clear plastic to catch half of all the rain falling in the experimental area. A control area nearby was not deprived of rainfall.

The researchers took a sample of 66 small trees, a 1- to 10-centimeter (a maximum of 4 inches) diameter, and a height of 1.3 meters (4 1/4 feet). Out of the large trees measuring 20 centimeters (8 inches) in diameter, 61 were sampled. 

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Results of the Study

Bartholomew says that their findings reveal the adaptability of small trees compared to giant trees. These smaller trees change their physiological response to changes in the environment. Because they grew up in drought conditions, they could have capabilities that could help them adapt to future droughts. This could ultimately let them succeed the older trees and take over as canopy trees, creating a more resilient forest.

The small trees in the experimental drought area exhibited an increase in their capacity to photosynthesize. They also had a 32 percent increase in leaf respiration and an increase of 15 percent in leaf mass compared to the control area's trees.

Implications for the Future

According to Bartholomew, if droughts can kill more giant trees, smaller trees should be able to adapt to less water availability and an increase in light. As their study found, they may have a remarkable capacity to do just that. However, some tree species also showed minimal adaptability.

More research is to be conducted to determine how this will shape the future of the incredibly diverse Amazon.

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