Old-growth forests and managed forests with old-growth features may provide climate change relief for some bird species, research from the Oregon State University College of Forestry suggests.
The study, led by former Oregon State doctoral student Hankyu Kim, builds on previous research led by co-author Matt Betts, a professor in the Department of Forest Ecosystems and Society, which showed that old-growth forests with large trees and a diversity of tree sizes and species. it can provide refuge for some types of birds threatened by hot weather.
The latest findings have important implications for conservation decisions in mature forests, scientists say, and are even more relevant because of the new Inflation Reduction Act, which calls for increased resources to map and protect forests former remains of the United States.
The research, published today in Global Change Biology, looked at forest “microclimates”. Microclimates are local atmospheric conditions, in areas ranging from a few square meters to many square kilometers, that differ from those of the environment.
Microclimates tend to be more pronounced in areas of rugged and varied topography, such as coastal areas, islands, and mountains such as the Oregon Falls Range, home of the HJ Andrews Experimental Forest where Kim and Betts did their research .
Scientists and collaborators from Oregon State OSU and the US Forest Service analyzed eight years of breeding bird abundance information from a HJ Andrews watershed, as such as subcanopy temperature readings and ground-based vegetation data and LiDAR. They concluded that in places with colder microclimates, some bird species tend to do better, a phenomenon they describe as a “buffering effect”.
Some species also fared better in places where the forest had more compositional diversity, called the “insurance effect,” because diversity helps ensure the presence of the insects that birds feed on when they need nutrition and energy the most, during the season of reproduction
“To my knowledge, this is the first empirical evidence of any effect of microclimate on songbird populations and of the insurance effect on free-ranging birds,” said Kim, now a postdoctoral researcher at the University of Wisconsin-Madison. Madison. “Each species may have a slightly different range of thermal optima, the range of thermal conditions they are comfortable with, and it could be the same for the interaction between forest ecosystems and birds.”
Under the current warming regime, he explained, some birds interact with the forest ecosystem for their own benefit, while others will struggle to breed there because food availability has changed for the worse.
The scientists found that for five of the 20 bird species they analyzed, trends in abundance tended to be neutral or less negative in colder microclimates, and the negative effects of warming on two species were reduced in places with greater diversity of forest composition.
The five species that benefited from the buffering effect were Swainson’s thrush, chestnut-backed grouse, hermit thrush, variegated thrush, and Wilson’s thrush. Wilson’s warbler and red crossbill were the two with statistical evidence of benefiting from the insurance effect.
“If plants emerge earlier in warm microclimates, causing arthropods to emerge earlier, there is a danger that migratory birds will not approach their breeding grounds with maximum food availability,” Betts said. “Since the timing of leaf emergence varies among plant species, forests with greater plant diversity often have a longer period of insect availability.”
The other 14 birds in the analyzes were dark-eyed junco, hermit thrush, McGillivray’s warbler, Pacific slope flycatcher, brown creeper, black-throated gray warbler, golden-crowned kinglet, Hammond’s flycatcher, hairy woodpecker, Pacific robin, red robin. Red-breasted Woodpecker, Red-breasted Sucker, Western Tanager and Yellow Warbler.
Seven of the 20 species showed overall declines in abundance over the eight-year study, 2011-18. Nine showed increases and four showed a detectable trend.
“Abundance trends for five species declined at a greater rate in warmer locations than in cooler areas,” Kim said. “This suggests that microclimates within forested landscapes provide refuge for these species. Declining species that are sensitive to warm conditions, such as Wilson’s warbler, hermit warbler and chestnut-backed grouse, appeared benefit more from the effects of shelters.”
Betts found it interesting that the Kim-led study — the results of which Betts said were “independently collected and more rigorous” than the research he led in 2017 — showed the same species in decline and the same species that benefit from old-growth forests. characteristics.
“The previous paper was less well done because we didn’t measure the microclimate directly,” Betts said. “Our hypothesis was that microclimate buffering should work for a large proportion of species in decline. This current paper is the first time this has been shown.”
Brenda McComb and Sarah Frey of the OSU College of Forestry and David Bell of the Forest Service’s Pacific Northwest Research Station also participated in this research, which was supported by the National Science Foundation.
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