Research by the Oregon State University College of Forestry indicates that old-growth forests and managed forests with old-growth characteristics could provide relief from climate change for some bird species.
The study, led by former Oregon doctoral student Hankyu Kim, builds on previous research led by co-author Matt Bates, professor in the Department of Forest Ecosystems and Society, which showed that ancient forests with large trees and a diversity of tree sizes and types can provide sanctuary for some species of climate-threatened birds. warming;
Scientists say the latest findings hold important implications for conservation decisions about mature forests, and are of even greater significance because of the new Inflation Reduction Act, which calls for increased resources to map and protect the remaining ancient forests in the United States.
The research, published today in Global Change Biology, looked at the “microclimes” of forests. Microclimates are local weather conditions, in areas ranging from a few square meters to several square kilometres, that differ from those in the surrounding area.
Microclimates tend to be most pronounced in areas of rugged and varied terrain such as coastal regions, islands, and mountains such as the Cascade Range in Oregon, home to the HJ Andrews Experimental Forest where Kim and Bates conducted their research.
OSU scientists and collaborators from Oregon and the United States Forest Service analyzed eight years of bird breeding abundance information from the HJ Andrews watershed as well as under-canopy temperature readings, on-ground vegetation data and LiDAR. They conclude that in locations with cooler microclimates, some bird species tend to do a better job—a phenomenon they describe as the “buffering effect.”
Some species also fare better in places where the forest has greater compositional diversity, referred to as the “insurance effect” because diversity helps ensure that the insects that birds feed on are present when they need the most nutrition and energy – during the breeding season.
“To my knowledge, this is the first experimental evidence of any climate effect on songbird populations, and the effect of insurance on free-range birds,” said Kim, who is now a postdoctoral researcher at the University of Wisconsin-Madison. “Each species may have a slightly different range of thermal optimum – the range of thermal conditions they are comfortable with – and it could be the same for the interaction between forest and bird ecosystems.”
He explained that under the current warming regime, some birds would interact with the forest ecosystem to their advantage, while others would find it difficult to breed there because the availability of food had changed for the worse.
The scientists found that for five of the 20 bird species they analyzed, abundance trends tended to be either neutral or less negative in colder climates, and the negative effects of warming were reduced for two species at sites with greater forest compositional diversity.
The five species that benefited from the buffering effect were the Swenson’s bird, the chestnut-backed titmouse, the hermit warbler, the variegated thrush and the Wilson’s bird. It was Wilson’s intruder bird and the red tick that had statistical evidence of benefit from the insurance effect.
“If plants germinate early in warm climates, causing arthropods to emerge earlier, there is a risk that migratory birds may mistime their breeding with food at its peak,” Bates said. “Because leaf timing varies across plant species, forests with greater plant diversity often have a longer period of insect availability.”
The other 14 birds in the analyzes were the dark-eyed junky, hermit thrush, McGillivray, Pacific flycatcher, brown creeper, gray black-throated warbler, golden-crowned king, hammond flycatcher, hairy woodpecker, Pacific bird Red-breasted nut-keeper, red-breasted bird, western tanger, yellow-rumped speculator.
Seven of the 20 species showed an overall decrease in abundance during the eight-year study, 2011-18. Nine showed increases and four showed a detectable trend.
“Trends in abundance for five species declined at higher rates in warmer locations than in cooler regions,” Kim said. This suggests that the local climates within the forested landscape provide a haven for these species. Lower species sensitive to warm conditions, such as the Wilson’s rookery, the hermit hermit and the chestnut-backed titmouse, seem to benefit most from the effects of the sanctuary. “
Bates found it intriguing that the study Kim led — whose results Bates said were “independently collected and more rigorous” than those in the research he led in 2017 — showed the same species in decline and the same species benefiting from growing forests. old features.
“The previous paper was of lower quality because we didn’t directly measure the microclimate,” Bates said. “Our hypothesis was that microclimate buffering should work for a high proportion of degraded species. This current paper is the first time it has been shown.”
Brenda McComb and Sarah Fry of the Ohio State University College of Forestry and David Bell of the Forest Service’s Pacific Northwest Research Station participated in this research, which was supported by the National Science Foundation.