Old growth forest in the Oregon Cascades

Old growth forest in the Oregon Cascades

Matt Betts/Oregon State University

Old-growth forests in the Northwest have the potential to make the extremes of climate change less damaging for wildlife. New research out of Oregon State University shows complex forests do a surprisingly good job of regulating temperature on the ground – even compared to fully mature tree plantations.  

“On a sunny day, if you were sitting underneath them, you’d get a similar amount of shade,” says study co-author Matt Betts, an Ecologist at OSU.  

But the kind of forest makes a big difference on temperature.  

“The more structurally complex the forest, the more big trees, the more vertical layers - the cooler it was,” he says.  

The research showed differences as much as 4.5 degrees on warm days. Old growth forests also held in heat during cold weather. Overall, these forests have a moderating effect on temperature extremes.  

One reason, researchers suspect, is that tree plantations, even mature ones, don’t have nearly the understory material – small trees, shrubs, ground cover – as more complex stands. Nor do these single-age plantations have a lot of big trees – unlike old growth stands.  

“We think one of the mechanisms causing this is thermal inertia,” Betts says. “That takes these trees longer to warm up and longer to cool down. And that could be providing some of the buffering capacity of these older forests.”  

Betts says these stands of old growth could provide refuges for temperature-sensitive wildlife in the face of climate change.  

“It gives us some hope that how we actually manage our forest, can influence positively those species that are declining,” he says.  

The study was published Friday in Science Advances.