Old-growth forests: A weapon against climate change

The soaring canopy and dense understory of an old-growth forest could provide a buffer for plants and animals in a warming world, according to a new study.

Comparing temperature regimes under the canopy in old-growth and plantation forests in the Oregon Cascades, researchers from Oregon State University found that the characteristics of old growth 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.

Landowners who include biodiversity as a management goal, the scientists said, could advance their aims by fostering stands with closed canopies, high biomass and complex understory vegetation.

Management practices that create these types of "microclimates" for birds, amphibians, insects and even large mammals could promote conservation for temperature-sensitive species, the authors wrote, if temperatures rise as a result of global warming.

"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," said lead author Sarah Frey.

Frey added, "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."

"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," said co-author Matt Betts. "So, the magnitude of the cooling effect of old-growth structure is somewhat surprising."

The researchers found that variations in the landscape, such as elevation and slope, helped to explain temperature differences over short distances of 100 feet or less. However, at broader scales, the characteristics of the forest itself exerted a significant influence.

The study is published in Science Advances.