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The fate of our forests: New tool predicts tree survival amidst drought

The survival of forests amidst increasing droughts due to climate change is a growing concern worldwide. Researchers at the University of California, Davis have developed a new method that can help predict which forests are likely to survive future droughts. 

This innovative approach links precipitation to tree growth, aiding in crucial decision-making about resource allocation as climate change alters snow and rainfall patterns, subsequently affecting forest health.

Significance of the study

Jessie Au, a postdoctoral scholar in the Department of Plant Sciences at UC Davis, explained the significance of this development. 

“If a forest is doing OK, but in the future we know it’s likely to get only half the average rainfall it used to get, we can calculate the likelihood it will die.” 

Au worked with Professor Troy Magney and their team to develop this tool. The goal is to assist forest managers as well as companies using forests for carbon offsetting, an increasingly popular practice to counteract greenhouse gas emissions.

Focus of the study 

Forests play a crucial role in carbon sequestration, as they absorb carbon dioxide from the atmosphere and convert it into food, storing the carbon in their trunks, roots, and leaves. 

However, adequate water supply is essential for trees to absorb carbon dioxide. In times of water scarcity, trees can temporarily rely on their reserves of stored carbon, similar to how humans survive on stored fat and muscle in times of starvation. 

Tipping point identified

This survival strategy can only sustain trees for a limited period, after which they reach a tipping point. If the drought persists beyond this point, the forest will eventually succumb.

This critical tipping point was identified by Au and her team during a study of a forest in California’s southern Sierra Nevada, which was severely impacted by the record-breaking drought from 2012 to 2015. 

Millions of trees across the American West perished during this period. The researchers correlated changes in precipitation during the drought with the life processes inside the trees and analyzed the lag time between the onset of drought stress and the trees’ response. 

How the research was conducted 

For their study, the team monitored precipitation, soil moisture, and temperature in the forest and measured the amount of carbon dioxide absorbed by the trees. 

Using a novel methodology called CARDAMOM (Carbon Data Assimilation with a Model of Model of carbon Allocation), the researchers linked this data to ascertain how much carbon the trees stored in their reserves, such as wood, roots, and leaves, and tracked how these reserves diminished as the drought progressed.

What the researchers discovered 

Remarkably, the trees appeared healthy and continued to survive on their reserves for several years after the onset of the drought in 2012. 

However, by 2015, a tipping point was reached: the trees had exhausted their reserves, and 80 percent of them were functionally dead, unable to convert carbon dioxide into food.

Future droughts 

The ongoing development of the CARDAMOM methodology promises to provide even more insights into tree physiology during droughts and other stressors, enabling predictions about how forests will fare in future droughts. 

“With this new methodology, we can now link drought to tree death later on, and we can assign a number to that risk,” said Au. “It’s helping us identify vulnerable spots and whether we can save them.”

By identifying forests at risk and understanding the mechanisms underlying their vulnerability, it may be possible to develop strategies to enhance their resilience and ensure their survival in a changing climate.

The study is published in the journal Global Change Biology.

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