Oregon study finds wildfire smoke comes with ‘unanticipated’ benefit for trees
PORTLAND, Ore. (KOIN) – As researchers look for ways to help forests become more resilient to hotter, more extreme climates, a new study from Oregon State University discovered an unexpected way to protect trees: Wildfire smoke.
During the summer of 2021, scientists worked to determine the effect forest canopy has on summer temperatures near ground level when they made the discovery.
While heat stress can harm tree seedlings, the researchers learned wildfire smoke can act as a barrier to warmer temps.
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“Our results show that while overstory canopy cover may help buffer temperature stress experienced by seedlings, extreme heat events and climate change still pose significant challenges – and that wildfire smoke can actually be beneficial,” said OSU Faculty Research Assistant Amanda Brackett.
Scientists studied 11 different stands of recently thinned, 50-year-old Douglas Fir in the Upper Blue River Watershed in western Oregon’s Willamette National Forest and measured temperatures at two centimeters above ground on south-facing slopes.
The study area was heavily affected by wildfire smoke in August 2021 from the Middle Fork Complex and Washington Ponds fires.
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Researchers used established heat stress responses of seedlings from lab studies to look at temperature-induced stress to conifer seedlings and germinating seeds in different canopy conditions.
According to the study, for every 10% increase in canopy cover, maximum temps at two centimeters were 1.3 degrees Celsius lower, and the odds of temps exceeding stress thresholds for regenerations fell by one-fourth, and total stress degree hours fell by 40%.
“This work shows that widespread smoke from wildfires can lead to unanticipated beneficial effects by reducing sunlight at the surface and thus lowering the temperatures experienced by vulnerable tree seedlings, even during extreme summer weather like the 2021 heat dome period,” said OSU professor Chris Still.
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“Those reductions are large enough to be worthy of attention when managing for tree regeneration,” Brackett furthered. “But data collected during the Pacific Northwest heat dome in June 2021 indicate that with various climate change scenarios and heat wave occurrences, temperatures will be unfavorable for regeneration regardless of canopy cover.”
Researchers noted that during the 2021 heat dome, the highest temp recorded near the soil surface was just over 135 degrees Fahrenheit.
Additionally, wildfire smoke’s impact on maximum and average near-surface temp was similar to temperature reduction caused by an increase of 15% in canopy cover, researchers said.
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The finding is in line with the idea that even though smoke can cause several concerns, fire is a natural forest occurrence with ecological benefits researchers noted.
“Smoke absorbs and scatters incoming solar radiation, reducing how much reaches the forest floor, but we did not anticipate seeing this level of impact,” Brackett said. “That extra cooling effect may be important during extreme heat events when canopy cover and topography do not provide enough protection from harmful and potentially lethal temperatures in the understory.”
Tree regeneration is a crucial part of creating healthy, multi-aged forests, researchers said, noting the study shows the need to consider conditions experienced by young seedlings when designing forest treatments.
“Managers need to understand how microclimate varies under a range of overstory conditions,” Brackett said. “Given climate predictions, scientists and managers have to look for opportunities to increase individual tree and forest-level resilience to a hotter and more extreme climate. Wildfire smoke will continue to affect ecosystems and while we documented an unanticipated benefit, more work is needed to untangle other potential impacts.”
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