Recent study challenges previous beliefs about forest resilience

Scientists have flipped the script and revealed that trees in humid regions are more sensitive to drought.

This holiday season brings some surprising news about Christmas trees. Scientists have found that globally, trees that grow in wetter regions are more sensitive to drought. This means that if your tree was grown in a humid climate, it has likely been damaged over generations.

Debate over drought tolerance of trees

Scientists have long debated whether arid environments make trees more or less tolerant of drought. It seems intuitive that trees living at the biological margin are most vulnerable to climate change. Because even the slightest bit of extra stress can send a tree over the brink. On the other hand, these populations may be better able to withstand drought because they are adapted to harsher environments.

The trees of this lush temperate forest in the Cascade Mountains of Washington state may be less drought tolerant than trees in drier regions of the South.Credit: Joan Dudney

Insights from new research

According to a new study published in the journal science Increased water availability could “kill” trees by reducing their ability to adapt to drought, according to researchers from the University of California, Santa Barbara and the University of California, Davis. “And that’s really important to understand when we think about the global vulnerability of forest carbon stocks and forest health.” said Joan Dudney, an assistant professor and ecologist. “You don’t want to be a ‘spoiled’ tree when faced with a major drought.”

Dudney and his co-authors predicted that trees growing in the driest regions would be more sensitive to drought because they were already living on the edge of their limits. Furthermore, climate change models predict that these regions will dry out more rapidly than wetter regions. This change in climate can expose trees to conditions beyond their ability to adapt.

Methodology: Tree ring analysis

To measure drought sensitivity, the authors analyzed 6.6 million tree ring samples from 122 trees. seed World wide. They measured whether a tree was growing faster or slower than average based on the width of its growth rings. They correlated these trends with historical climate data such as precipitation and temperature.

The team then compared different regions’ responses to drought. “As you move to the drier edge of a species’ range, trees become less and less sensitive to drought,” said lead author Robert Heilmeyer, an environmental economist with the Environmental Research Program and the Bren School. he said. “Those trees are actually very resilient.”

Dudney, Heilmeyer, and their co-author Frances Moore were partially inspired by UCSB professor Tamma Carleton’s research on the effects of climate change on humanity. “This paper highlights the value of interdisciplinary scientific research,” added Moore, an associate professor at the University of California, Davis. “We applied economics methods originally developed to study how people and businesses adapt to changing climate, and applied them to ecological contexts to study the sensitivity of forests to drought. could be applied to.”

“A heat wave is likely to kill more people in a cool place like Seattle than in a hot city like Phoenix,” Heilmeyer said. It’s already quite hot in the Southwest, with a scorching heatwave occurring. But cities in the region are adapted to extreme climates, he points out. We now know that forests exhibit similar trends.

Impact on warm regions

Unfortunately, temperate regions are expected to become disproportionately drier in the coming decades. “Significant parts of the species’ ranges will be faced with entirely new climates, a phenomenon that these species do not find anywhere else in their ranges today,” Heilmeyer explained. The authors found that in 2100, 11% of the average species’ range will be drier than the driest part of its historical range. For some species, this increases to 50% or more.

“Broadly speaking, our study highlights that very few forests will be immune to the effects of climate change,” Dudney said. “Even wet forests are under more threat than we realize.”

But there’s also the other side of the coin. This species stores drought-tolerant resources in drier parts of its range and has the potential to strengthen forests in wetter regions. Previous research UCSB researchers have revealed that many species have the ability to adapt to environmental changes. But these researchers also discovered that trees move slowly from one generation to the next. This means that human intervention, such as assisted migration, may be required to take advantage of this genetic diversity.

Christmas tree and the fate of the forest

Whether the Christmas tree lives in a dry or humid region, its growth may decrease in the future. But understanding how trees respond to climate change can help secure the future of Tannenbaum and its wild trees.

Reference: “Drought sensitivity of mesic forests increases vulnerability to climate change” by Robert Heilmeyer, Joan Dudney, and Frances C. Moore, December 7, 2023. science.
DOI: 10.1126/science.adi1071