Lead author and ecologist Matt Betts tracked songbird populations in different kinds of forests – including old growth and mature tree plantations.
“We asked whether or not those declines could be mediated by what forest type is out there. And the old growth-associated landscapes tended to show reduced declines in the face of warming,” he said.
The birds, the Wilson’s and hermit warblers, have been in steady decline over the past three decades, especially in areas where average summertime temperatures have risen.
Researchers know that old-growth forests are cooler in the summer than tree plantations, even mature ones. The difference can be about 5 degrees Fahrenheit.
The canopy cover of these forests may appear similar, but study co-author Sarah Frey says the difference may be in the layers.
“Way up at the tippy-top, you’ll have these big old-growth Doug firs with most of their branches and needles up there, and then there’s going to be shorter trees, which would have their canopies lower. Then there’s shrubs. So there just a lot more variability,” she said.
The sheer volume of tree and plant mass in old-growth forests could also serve as a heat sink.
The researchers say cooler forests act as thermal refuge that may provide more food for the birds.
The research suggests that encouraging and preserving older complex forests could help songbirds weather warming conditions in the region.
The paper is published in the journal Diversity and Distributions.