Climate change is expected to have a dire impact on global biodiversity, but these predictions are derived from models applied at global scales that can miss some important nuances, according to a study published in the journal Science Advances last month.

A team comprised of researchers from Oregon State University and the Pacific Northwest Research Station of the U.S. Forest Service conducted the study at the H.J. Andrews Experimental Forest in the Oregon Cascades east of Eugene.

By comparing temperatures under the canopy in old-growth and plantation forests, the researchers found that the characteristics of old-growth forests reduce maximum spring and summer air temperatures as much as 2.5 degrees Celsius (4.5 degrees Fahrenheit) compared to those recorded in younger, second-growth forests.

The towering canopies and dense understories of old-growth forests might be able to help protect biodiversity as global temperatures continue to rise, according to new research.

Climate change is expected to have a dire impact on global biodiversity, but these predictions are derived from models applied at global scales that can miss some important nuances, according to a study published in the journal Science Advances last month.

“Such models lack the capacity to incorporate microclimate variability, which is critical to biodiversity microrefugia,” the authors write. “In forested montane regions, microclimate is thought to be influenced by combined effects of elevation, microtopography, and vegetation, but their relative effects at fine spatial scales are poorly known.”

A team comprised of researchers from Oregon State University (OSU) and the Pacific Northwest Research Station of the U.S. Forest Service (USFS) conducted the study at the H.J. Andrews Experimental Forest in the Oregon Cascades east of Eugene.

By comparing temperatures under the canopy in old-growth and plantation forests, the researchers found that the characteristics of old-growth forests reduce maximum spring and summer air temperatures as much as 2.5 degrees Celsius (4.5 degrees Fahrenheit) compared to those recorded in younger, second-growth forests.

“Though it is well-known that closed-canopy forests tend to be cooler than open areas, little is known about more subtle temperature differences between mature forest types,” Sarah Frey, a postdoctoral scholar in the OSU College of Forestry and the lead author of the study, said in a statement. “We found that the subtle but important gradient in structure from forest plantations to old growth can have a marked effect on temperatures in these forests.”

Frey and team say that variations in the landscape like elevation and slope can account for temperature differences over short distances of 100 feet or less. But at broader scales, the characteristics of the forest itself have a much more significant influence than has previously been ackowledged.

“As expected, elevation strongly predicted temperatures, but vegetation and microtopography also exerted critical effects,” they wrote. “Old-growth vegetation characteristics, measured using LiDAR (light detection and ranging), appeared to have an insulating effect… These cooling effects across a gradient in forest structure are of similar magnitude to 50-year forecasts of the Intergovernmental Panel on Climate Change and therefore have the potential to mitigate climate warming at local scales.”

The researchers conclude that conservation strategies should focus on preserving old-growth characteristics such as closed canopies, high biomass, and complex understory. In other words, the way forests are managed is crucial, as curbing current rates of primary forest loss can help maintain these “microclimates” and therefore enhance the survivability of amphibians, birds, insects, and even large mammals in mountainous systems, despite global warming.

“To the untrained eye, plantations might look similar to old-growth forest in terms of the aspects that are well known to influence temperature, particularly canopy cover,” Matt Betts, Oregon State professor and co-author of the study, said in a statement. “So, the magnitude of the cooling effect of old-growth structure is somewhat surprising.”

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