Swiss Forest Study Shows Some Deciduous Species May Be Able To Adapt To Extreme Heat, But Heat + Drought Deadly
EDIT
Recent hot and dry summers have damaged forests on a scale visible from space. Leaves dried, scorched, faded and even died weeks or months ahead of schedule, and in a new study published Monday, scientists identified climate thresholds beyond which leaves are irreversibly damaged. The researchers closely examined how individual leaves of beech and oak trees respond to warming. The findings suggest some fundamental limits to how some deciduous trees and leaves cope with climate stress, said lead author Alyssa T. Kullberg, a postdoctoral researcher in the plant ecology research lab of the Swiss Federal Institute for Forest, Snow and Landscape Research. Many important tree species may be able to adapt to the additional 4 to 5 degrees Fahrenheit heating expected by 2100—if they have enough water. “But when heat and drought come together, that’s when the system breaks down,” Kullberg said.
The researchers used an open-air forest lab near Zürich, Switzerland, to grow young trees in rows of glass chambers. Both oak and beech are economically and culturally valuable in Europe. Conditions in some containers tracked the natural environment, while others were warmed by about 5 degrees Celsius, with water regulated to simulate drought or normal conditions. Sensors and cameras mounted above tracked leaf temperatures all summer while the scientists moved from tree to tree, measuring how water flows through the leaves and how much strain they could tolerate. Custom-built cameras zoomed in on small patches of leaf surface to capture the exact moment they “scorched,” when green tissue suddenly turns brown.
Kullberg said the scientists wanted to track every aspect of leaf responses to the controlled heating, from how leaves cool themselves to the point at which visible damage begins. One of the goals was to determine whether early exposure to extreme heat and drought might help young trees toughen up over time. And in some ways, they did. The beech and oak adjusted their physiology and even raised the maximum temperatures their leaves could survive, Kullberg said. “They increased their thermal tolerance, but it was still not enough,” Kullberg said. The combination of heat and drought in the warmed chambers still pushed leaf temperatures well beyond those new limits, she added.
The study shows that even moderate water shortages can trigger a “downward spiral” in how leaves and trees respond to heat, said plant physiologist Kevin Hultine, director of research in the Department of Research, Conservation and Collections at the Desert Botanical Garden in Phoenix. When drought and heat coincide, he said, trees can quickly lose their ability to regulate temperature, reducing growth and increasing the risk of dieback. “Unfortunately, these results tell us that in the short-term, forest ecosystems will likely fall into an altered state with climate change,” said Hultine, who was not an author of the new paper. “That will result in reduced biodiversity, reduced carbon sequestration and increased risk of megafires.”
EDIT
https://insideclimatenews.org/news/06042026/europe-forests-heat-emissions-study/