As climate warms, old-growth forests could give birds refuge

With temperatures expected to rise over the coming decades, some bird species could find it difficult to cope and suffer declines. But researchers in the Pacific Northwest found that old-growth forest may serve as a sanctuary for birds sensitive to climate change, and they suggested that protecting these areas could benefit these species in danger of decline.

“Old-growth stands could buffer populations against warming and dampen declines,” said Matthew Betts, lead author on the study published in the journal Diversity and Distributions.

In 2015, Betts — a professor at Oregon State University’s College of Forestry — and his fellow researchers began examining temperature, Breeding Bird Survey population counts and satellite imagery of forest cover spanning the Pacific Northwest for the past 30 years. They focused on 13 species associated with the region’s older forests, including the hermit warbler (Setophaga occidentalis) and Wilson’s warbler (Cardellina pusilla).

Those two birds showed strong negative responses to climate warming, Betts said, but their populations declined less in old growth.

“It seems to be buffering the effects of climate on these birds,” Betts said, possibly because the old-growth stands tend to be cooler during the summer than younger forests. “That’s made for better habitat for birds in landscapes that have warmed a lot.”

Given the difficulty of reducing greenhouse emissions to curb global warming, Betts said, old-growth forests could help some species that are climate sensitive.

He and his colleagues are gathering detailed data at Andrews Forest in Oregon to verify their landscape-scale findings and delving into why old-growth stands are cooler and how birds adapt to hotter temperatures by moving to these areas.

“Maybe old-growth has more cool nooks and crannies where birds buffer themselves against warming temperatures,” Betts said.