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Small trees give hope for rainforests

Small trees give hope for rainforests

Droughts in the Amazon affect larger trees more severely because they are more likely to die from hydraulic failure. Credit: David Bartholomew

Small trees that grow up in drought conditions can form the basis for more drought-resistant rainforests, new research suggests.

Severe and prolonged droughts are becoming more common in the Amazon and often kill large trees that form the forest roof.

But a new study, led by the University of Exeter, suggests small trees adapt better to drought and can grow into a new generation to help the rainforest survive.

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

“Conditions in the Amazon are changing due to climate change, and trees will have to adapt to survive,”

; said lead author David Bartholomew, Exeter’s Global Systems Institute.

“Our results show that small trees are more capable of changing their physiology in response to environmental changes than their larger neighbors.

“Once they have grown up in drought, these trees can develop properties that help them cope with future droughts – even when they are fully grown.

Small trees give hope for rainforests

Under prolonged drought conditions, the dense roof becomes more open and more light reaches the lower layers of the forest. Credit: David Bartholomew

“Ultimately, this could enable them to form the next generation of tree roofs, which could lead to increased total resilience in the forest.”

The study examined trees in a 15-year-old Amazon drought experiment, where clear plastic panels capture 50% of the precipitation.

Researchers sampled 66 small trees (1-10 cm in diameter at a height of 1.3 m from the ground) and 61 large trees (more than 20 cm in diameter) in the drought experiment area and a nearby control area without rain 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.

“This long-term experiment has shown that large trees are quite vulnerable to drought and probably will not survive if drought continues to become more common and more severe,” said Bartholomew, a Ph.D. student at NERC GW4 + doctoral student partnership.

However, relatively little is known about the response of small understorey trees that may be crucial in determining the future of tropical forests.

Small trees give hope for rainforests

The drought experiment stops 50% of the water that reaches the ground. Credit: David Bartholomew

“The support of an intact rainforest is usually a dark and humid environment.

“Trees found in low light will normally regulate their photosynthetic ability to conserve resources.

“But if drought causes larger trees to die, these trees must be adapted to both declining availability and increased light.

“Our study suggests that they have a remarkable ability to do this.”

The responses from 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 could change the design of the famous diverse rainforest in the Amazon in the future.

The essay was published in the journal Plant, cell and environment, is entitled: “Small tropical forest trees have a greater capacity to adapt carbon metabolism to prolonged drought than large tree roofs.”

Some tree species retain stored water, limiting root growth to survive three months without water

More information:
David C. Bartholomew et al., Small tropical forest trees have a greater capacity to adapt carbon metabolism to prolonged drought than large chapel trees, Plant, cell & environment (2020). DOI: 10.1111 / pce.13838

Provided by the University of Exeter

Quote: Small trees give hope for rainforests (2020 5 August) retrieved 6 August 2020 from https://phys.org/news/2020-08-small-trees-rainforests.html

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