URBANA, Ill. (U.S.A.) — All over the world, from Oregon’s old-growth forests to Queensland’s eucalyptus groves, creatures depend on trees for shelter. A new analysis from the University of Illinois Urbana-Champaign suggests that as the climate destabilizes, the world’s trees may become an even more important respite. That’s because, the study finds, trees everywhere buffer their animal tenants from temperature extremes.
“We’ve seen mass mortality events in both birds and bats in recent years due to extreme heat. Our meta-analysis finds that, on average, tree cavities can stay 3-4 degrees Celsius cooler than the outside air, with some larger or deeper cavities staying up to 15 degrees cooler,” said senior study author Joy O’Keefe, associate professor and wildlife Extension specialist in the Department of Natural Resources and Environmental Sciences (NRES) and Illinois Extension, both part of the College of Agricultural, Consumer and Environmental Sciences at Illinois.
Three or four degrees doesn’t sound like a lot, but when the outside air approaches deadly extremes, that difference can keep cavity-dwelling animals alive. And not just on hot days. Tree cavities also provide slightly warmer microclimates when it’s cold, an especially important feature for some animals during gestation or when babies are left alone in the nest.
O’Keefe and her collaborators have spent more than a decade studying natural and artificial roosts for bats, focusing much of their attention on the animals’ ability to thermoregulate in various roost configurations. Among other insights, they’ve shown that natural roosts — tree cavities, peeling bark, and other tree crevices — offer greater protection from temperature extremes than most artificial roosts.
Most of the team’s work has taken place in the eastern half of the U.S., but temperature extremes are a global concern. They wondered: Do tree cavities offer the same thermal protections to arboreal animals everywhere? The answer could guide forest management decisions worldwide.
Conservation scientist and NRES graduate Katrina Cotten worked with O’Keefe to conduct the first global literature review and analysis on the temperature buffering capacity of tree cavities. She extracted data from 36 relevant studies, spanning 65 years and five continents. If the study presented temperature differences inside and outside of tree cavities, it went into Cotten’s meta-analysis.
“This was a rare case where the data showed us exactly what we thought would happen,” O’Keefe said. “Everywhere we looked, trees were great for buffering outside air temperature extremes.”
Cotten notes that her literature search necessarily focused on the Global North, as there were no studies of tree cavity temperatures in South America, Asia, or much of Africa, apart from South Africa.
“There’s good reason to suspect that trees do the same things in those places, but it would be nice to study more types of trees and more types of environments,” she said. “It would be especially great to study trees in biodiversity hotspots, which also happen to be areas that are underrepresented in research.”
Despite these data gaps, the researchers say there’s plenty of evidence to suggest that prioritizing trees, especially large or old ones, is a smart management decision to protect tree-dwelling animals.
“Forest managers should focus on protecting and regenerating natural habitats for animals, especially in areas where you get heat waves that can result in mass mortality events,” said study co-author Reed Crawford, postdoctoral researcher in O’Keefe’s group.
Crawford notes that the study underscores how nest boxes and other artificial roosts fail to replicate tree cavities.
“We know bat boxes almost always exceed outside air temperature, and then they don’t retain that heat at night,” he said. “If people are compelled to use artificial roosts in their conservation plans, we need to improve their design to better replicate what's happening in nature and try to keep those animals safe.”
The study, “A global review of the capacity of tree cavities to buffer temperature extremes,” is published in Forest Ecology and Management [DOI: 10.1016/j.foreco.2026.124180].
Research in the College of ACES is made possible in part by Hatch funding from USDA’s National Institute of Food and Agriculture.