Protecting forests at the forefront of the battle against climate change

Forests remove about a third of greenhouse gas emissions caused by human activities. Credit: Steven Kamenar via Unsplash

Forests help combat global warming, but they are also threatened by it. Many tree species struggled last summer as much of Europe was hit by heatwaves and severe drought, considered the worst in the last 500 years.

Olive trees, known for their ability to resist aridity, have also suffered. Spain is the world’s leading producer of olive oil, but many Spanish farmers expect their olive oil yields to decline by up to 50% this year.

In this context, Horizon researchers are trying to understand more about how trees respond to drought as part of the fight against climate change.

Carbon sinks

Existing forests already remove about a third of greenhouse gas emissions caused by human activities. A worldwide reforestation program could do the same for nearly a third of the discharges that remain in the atmosphere.

“If you look back over the past 10 years or so, there have been a number of events where a severe drought has resulted in the large-scale death of trees in the forests.” said Dr Jaideep Joshi, of the Plant-FATE project, who is studying plant traits to protect forests from climate change.

Planting billions of trees is a relatively inexpensive way to tackle the climate crisis, according to a study on the potential of global forest cover to mitigate climate change.

But as drought spreads, forests around the world are at risk. In Europe, between 1987 and 2016, 500,000 hectares of forest were cleared due to drought.

Joshi led the Horizon-funded Plant-FATE project, which broke new ground when it comes to predicting the impact of drought on trees of all kinds.

Resilience of the tree

A major limitation of current models is that they rarely consider trees’ ability to adapt to drought conditions and how resilience can differ between species. This leads to inconsistencies in the projection of how forests will respond to future climate scenarios.

“This is where the greatest uncertainty currently lies,” said Dr. Joshi. “You have this whole ecosystem of mixed species – we tried to bring all of this together in a simple but complete modeling framework.”

A model serves as a tool to simulate the results, and she believes her team’s model will be particularly useful when it comes to planning tree planting programs. This is because it can signal the carbon capture and storage potential of different species over the next 50-100 years, when climatic conditions will be different from what they are today.

“It could help make the right choice of which species to plant or where to plant them,” said Dr. Joshi. “It is the most promising conservation application of our model.”

In their model, the Plant-FATE researchers incorporated the ability of trees to adapt to climate change and examined a range of time scales.

In shorter periods of weeks or months, for example, trees exposed to drought can lose their leaves to conserve water (because water evaporates through pores on the surface of the leaves) in what is known as a “false autumn.” “.

New wood

But over longer times, trees can grow new wood with different properties more suited to drought conditions.

Dr. Joshi and his team also took the size into account. For example, some responses occur in specific parts of a tree such as roots and leaves, while others occur at the level of an entire species.

Protecting forests at the forefront of the battle against climate change

Tree mortality in a coniferous forest in the western United States. Credit: Laura Fernández de Uña, 2020

To test their comprehensive model, Dr. Joshi and his colleagues used data from an Amazon rainforest site containing about 400 species in an area of ​​5,000 square meters. They found that their model predictions closely matched what happened in real life at the site.

It marks the first time that a vegetation model has worked realistically on different time scales using very few parameters, according to Dr. Joshi, a researcher at the International Institute for Applied Systems Analysis in Laxenburg, Austria.

“It gives you the ability to predict forest performance under unknown conditions,” he said. “This makes it much more useful to predict the response of global forests to future climate scenarios.”

Tall trees

While tall trees are often considered more vulnerable to drought conditions than shorter ones, much remains to be discovered as to why and to what extent a tree’s height affects its drought resistance.

Dr Laura Fernández de Uña leads the Horizon-funded DISTRESS project, which is examining how a tree’s ability to carry water changes with height and how this could affect responses to drought.

She and her colleagues are ready to shake some conventional wisdom in the field.

“We see some differences between individual trees and also between species types,” said Dr Fernández de Uña, a postdoctoral fellow at CREAF public research center in Barcelona, ​​Spain.

Unsurprisingly, research confirms that it is more difficult for water to reach the heights of taller trees. Even under normal conditions, gravity is a fundamental impediment.

Air bubbles

During a drought, it is more difficult for trees to draw water from dry soil and pull it upwards. This increases the risk of water-carrying ducts sucking in air bubbles, which can block the flow (similar to embolisms in human blood vessels). If bubbles occur, parts of a tree may be denied water and die.

Additionally, tall trees in a forest are exposed to more heat and wind and less humidity. “The condition of the canopy itself is drier than for a smaller tree in the undergrowth,” said Dr Fernández de Uña. “All of this is bad for tall trees during a drought.”

However, past research indicates that tall trees can adapt to heat and water stress or even cope better than small trees. For example, they are able to expand their water-conducting pipes to get more flow along their long trunks.

Well rooted

Additionally, larger trees have more roots reaching greater depths, allowing access to water even when levels in the raised ground are low.

They also tend to have thicker trunks, which allow larger trees to store more carbohydrates and water.

For Dr Fernández de Uña, this all shows that, contrary to common assumptions, tall trees have a fighting chance when temperatures rise and water is scarce for prolonged periods.

“They are able to adapt and push their limits,” he said. ‘We need to be more open about how they might react to drought. If it wasn’t worth being tall, the trees wouldn’t grow tall.’

The research in this article was funded through the EU’s Marie Skłodowska-Curie Actions (MSCAs). The article was originally published in Horizonthe EU journal on research and innovation.


Research shows that some trees overheat in warmer rainforests


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Citation: Protecting forests at the forefront of the battle on climate change (2022, October 16) retrieved October 16, 2022 from https://phys.org/news/2022-10-forests-front-line-climate-change.html

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