Tree diversity may help forests better withstand climate extremes
A study of more than 88,000 U.S. forest plots linked greater tree diversity to stronger resistance and recovery, especially during drought.
Trees in California’s Sierra Nevada forest are “cheating death” and longer matching their climate. Veuer’s Maria Mercedes Galuppo has the story.
Forests that have a greater diversity of trees might be more protected against climate extremes, evidence from a recent study suggests.
Forest ecosystems are threatened by "compound extremes," which means extreme heat occurred during the same year as either drought or excessive moisture. These combined threats result in lower forest recovery, how closely productivity returns to normal the following year, and resistance, how well they withstand a disturbance, as opposed to a single danger.
Published in Nature Communications, the study covered 88,116 forest plots spanning 22 ecoregions across the contiguous United States, using data from the U.S. Forest Service’s Forest Inventory and Analysis program and "satellite-based stability estimates."
The analysis also measured recovery one year after an extreme event. Between 2001 and 2020, compound heat and moisture extremes were detected at least once across all the plots.
In this Tuesday, Sept. 29, 2009 photo, colorful aspen trees stand straight into the blue sky during the autumn season change near Buena Vista, Colo. (AP Photo/Nathan Bilow)
Combined climate extremes amplify threats to forests
The researchers found that higher tree diversity was associated with greater resistance and recovery under both individual and compound extremes.
“Tree species diversity consistently enhances forest ecosystem resistance to various types of climate extremes, with more diverse communities generally experiencing smaller proportional productivity changes under both individual and compound extremes,” the authors said.
Early morning autumn light near Killington, Vermont.(Getty Images/DenisTangneyJr)
The findings also suggest that focusing only on individual climate extremes will likely underestimate the impacts of compound extremes. Tree diversity may play a vital role in reducing these threats under future climate conditions.
Out of the two compound extremes, heat and drought were the more damaging combination, producing slightly lower resistance and weaker recovery than heat paired with excessive moisture. This could be because extreme drought directly impacts ecosystem functions by restricting growth and photosynthesis, reducing water supply and causing "oxidative stress and plant death." These impacts are more harmful than those of excessive moisture, which mainly acts through oxygen deficiency.
The effects of the compound extremes, specifically heat and drought, on forest ecosystem functioning were also determined to be "synergistic." This means the combined effects were often worse than the effects of each extreme added together. Among the relevant plots, heat and drought had synergistic effects in 72 percent during the extreme year, compared with 53 percent for heat and excessive moisture.
Diverse forests may gain 'biological insurance' against extremes
Biodiversity’s apparent benefit was strongest during drought alone and compound heat and drought, according to the results. The relationship between tree species richness and forest recovery remained positive after researchers accounted for factors including soil properties, average climate conditions, elevation and stand age.
“In this study, stand age for each plot represents the approximate age of the dominant age class and thus captures broad contrasts between young and older forests,” the authors explained.
An aerial view shows fall foliage at its peak, with vibrant red, orange and yellow leaves transforming the landscape into a colorful autumn scene in Westmore, Vermont, USA, on Oct. 3, 2026. (Photo by Lokman Vural Elibol/Anadolu via Getty Images)
In addition to biodiversity, temperature, precipitation, soil properties, stand age and topography were associated with forests’ resistance to and recovery from climate extremes. Although tree species diversity had relatively low explanatory power for both measures, the researchers said it remains an important management objective because it can be supported through conservation and forestry practices.
"Confronted with more harmful compound extremes, tree species diversity may continue to provide biological insurance effects that buffer ecosystems against the adverse impacts of extreme events," the study's authors said. "Our work underlines the crucial role of biodiversity in maintaining ecosystem resistance, highlighting the fact that diverse forests are better equipped to withstand and recover from the increasing severity of compound extremes under future climate scenarios."
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