Protecting Species of Birds from Climate Change, According to Science

Protecting Species of Birds from Climate Change, According to Science

New research from the Oregon State University College of Forestry suggests that old-growth forests and managed forests with old-growth characteristics can offer relief from climate change for certain bird species.

This study, led by a former Oregon State doctoral student named Hankyu Kim, expands on the work of co-author Matt Betts, a professor in the Department of Forest Ecosystems and Society, who found that old forests with large trees and a variety of tree sizes and species can provide refuge to some species of birds threatened by a warming climate. Experts say the new findings have crucial relevance for conservation decisions involving old-growth forests, especially in light of the new Inflation Reduction Act’s mandate for more funding to be allocated toward mapping and protecting these forests.

Forest “microclimates” were the focus of today’s study, published in Global Change Biology. Microclimates are distinct local weather patterns, spanning from a few square meters to many square kilometers. Kim and Betts conducted their investigation in the HJ Andrews Experimental Forest in Oregon’s Cascade Range, which is known for its prominent microclimates due to the region’s steep and varied topography.

Researchers from Oregon State University and the United States Forest Service looked at sub-canopy temperature readings, ground and LiDAR-based vegetation data, and eight years’ worth of data on the number of breeding birds in the HJ Andrews watershed. The researchers called this phenomenon the “buffering effect,” and it explained why certain bird species fared better in areas with cooler microclimates.

New research from the Oregon State University College of Forestry suggests that old-growth forests and managed forests with old-growth characteristics can offer relief from climate change for certain bird species. This study, led by a former Oregon State doctoral student named Hankyu Kim, expands on the work of co-author Matt Betts, a professor in the Department of Forest Ecosystems and Society, who found that old forests with large trees and a variety of tree sizes and species can provide refuge to some species of birds threatened by a warming climate. Experts say the new findings have crucial relevance for conservation decisions involving old-growth forests, especially in light of the new Inflation Reduction Act's mandate for more funding to be allocated toward mapping and protecting these forests. Forest "microclimates" were the focus of today's study, published in Global Change Biology. Microclimates are distinct local weather patterns, spanning from a few square metres to many square kilometres. Kim and Betts conducted their investigation in the HJ Andrews Experimental Forest in Oregon's Cascade Range, which is known for its prominent microclimates due to the region's steep and varied topography. Researchers from Oregon State University and the United States Forest Service looked at subcanopy temperature readings, ground and LiDAR-based vegetation data, and eight years' worth of data on the quantity of breeding birds in the HJ Andrews watershed. The researchers called this phenomena the "buffering effect," and it explained why certain bird species fared better in areas with cooler microclimates. Some species also did better in forests with greater compositional variety, a phenomenon known as the "insurance effect" since it increases the likelihood that the insects the birds eat would be present when they need them the most (during breeding season). A postdoctoral researcher at the University of Wisconsin-Madison, Kim, stated that "to my knowledge, this is the first empirical proof of any microclimate effect on songbird populations, and of the insurance effect on free-ranging birds." In terms of how birds and forests interact, "each species may have a somewhat varied range of thermal optima" (the range of temperature conditions within which the species thrives). Some birds gain from interacting with the forest ecosystem under the current warming regime, he said, while others will find it difficult to reproduce there due to changes in the availability of food. Five of the twenty bird species studied showed neutral or less negative abundance trends in colder microclimates, while the negative effects of warming on two species were mitigated in sites with greater forest compositional variety, according to the researchers. The Swainson's thrush, chestnut-backed chickadee, hermit warbler, variable thrush, and Wilson's warbler were the five species that benefited from the buffering effect. Two species, the Wilson's warbler and the red crossbill, were found to have statistically significant insurance effect benefits. Betts warns that migratory birds could get their breeding schedules mixed up if plants leaf out sooner in warm microclimates, leading to the earlier emergence of arthropods. To paraphrase, "because leaf-out timing varies by plant species, forests with more plant diversity frequently have a longer period of insect availability." Other species analysed included the dark-eyed junco, hermit thrush, McGillivray's warbler, Pacific-slope flycatcher, brown creeper, black-throated grey warbler, golden-crowned kinglet, Hammond's flycatcher, hairy woodpecker, Pacific wren, red-breasted nuthatch, red-breasted sapsucker, western tanager, and yellow-rumped warbler. From 2011 to 2018, researchers saw a general fall in abundance for seven of the study's twenty species. There were nine cases of growth, and four cases of discernible trend. Five of the species saw a steeper fall in abundance as temperatures rose, as stated by Kim. That indicates that microclimates in forest cover do serve as refuges for some species. The refugia effect appeared to be most helpful for declining species that are sensitive to warm weather, such as the Wilson's warbler, the hermit warbler, and the chestnut-backed chickadee. Betts found it intriguing that the same species in decline and the same species benefiting from forests with old-growth features were identified in the study headed by Kim, whose data Betts said were "collected independently and more carefully" than those in the research he did in 2017. Because "we didn't assess microclimate directly" in the earlier work, "it was less properly done," Betts added. We hypothesised that microclimate buffering would be effective for many of the species in steep decline. This paper presents the first evidence of this phenomenon. The OSU College of Forestry's Brenda McComb and Sarah Frey, together with the Forest Service's David Bell of the Pacific Northwest Research Station, all contributed to this NSF-funded study.

Some species also did better in forests with greater compositional variety, a phenomenon known as the “insurance effect” since it increases the likelihood that the insects the birds eat would be present when they need them the most (during breeding season).

A postdoctoral researcher at the University of Wisconsin-Madison, Kim, stated that “to my knowledge, this is the first empirical proof of any microclimate effect on songbird populations, and of the insurance effect on free-ranging birds.” In terms of how birds and forests interact, “each species may have a somewhat varied range of thermal optima” (the range of temperature conditions within which the species thrives).

Some birds gain from interacting with the forest ecosystem under the current warming regime, he said, while others will find it difficult to reproduce there due to changes in the availability of food. Five of the twenty bird species studied showed neutral or less negative abundance trends in colder microclimates, while the negative effects of warming on two species were mitigated in sites with greater forest compositional variety, according to the researchers.

The Swainson’s thrush, chestnut-backed chickadee, hermit warbler, variable thrush, and Wilson’s warbler were the five species that benefited from the buffering effect. Two species, Wilson’s warbler, and the red crossbill were found to have statistically significant insurance affect benefits.

Climate Change Buffer: Research shows protection for certain birds

Betts warns that migratory birds could get their breeding schedules mixed up if plants leaf out sooner in warm microclimates, leading to the earlier emergence of arthropods. To paraphrase, “because leaf-out timing varies by plant species, forests with more plant diversity frequently have a longer period of insect availability.” Other species analyzed included the dark-eyed junco, hermit thrush, McGillivray’s warbler, Pacific-slope flycatcher, brown creeper, black-throated grey warbler, golden-crowned kinglet, Hammond’s flycatcher, hairy woodpecker, Pacific wren, red-breasted nuthatch, red-breasted sapsucker, western tanager, and yellow-rumped warbler.

From 2011 to 2018, researchers saw a general fall in abundance for seven of the study’s twenty species. There were nine cases of growth, and four cases of discernible trend. Five of the species saw a steeper fall in abundance as temperatures rose, as stated by Kim. That indicates that microclimates in forest cover do serve as refuges for some species. The refugia effect appeared to be most helpful for declining species that are sensitive to warm weather, such as Wilson’s warbler, the hermit warbler, and the chestnut-backed chickadee.

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Betts found it intriguing that the same species in decline and the same species benefiting from forests with old-growth features were identified in the study headed by Kim, whose data Betts said were “collected independently and more carefully” than those in the research he did in 2017. Because “we didn’t assess microclimate directly” in the earlier work, “it was less properly done,” Betts added. We hypothesized that microclimate buffering would be effective for many of the species in steep decline. This paper presents the first evidence of this phenomenon.

The OSU College of Forestry’s Brenda McComb and Sarah Frey, together with the Forest Service’s David Bell of the Pacific Northwest Research Station, all contributed to this NSF-funded study.