by PORTLAND, Ore. (AP) –
As native trees in the Pacific Northwest die from climate change, the U.S. Forest Service, Portland, Oregon and citizen groups around Puget Sound are turning to a deceptively simple climate adaptation strategy called “assisted migration.” .
As the world’s climate warms, tree growing ranges in the Northern Hemisphere are expected to move further north and higher in altitude.
Of course, trees cannot get up and walk to their new climatic homes. This is where aid migration is expected to lend a helping hand.
The idea is that humans can help trees keep up with climate change by moving them to more favorable ecosystems faster than the trees could migrate on their own.
However, not everyone agrees on what kind of assisted migration the region needs — or that it’s always a good thing.
In the Pacific Northwest, a divide has emerged between groups advocating an assisted migration that would help struggling native trees, and one that could replace native species on the landscape with trees from the south, including coastal redwoods and giant sequoias.
“There’s a big difference between assisted population migration and assisted species migration,” said Michael Case, a forest ecologist at the Virginia-based Nature Conservancy.
Case currently runs an assisted population migration experiment at the Conservancy’s Ellsworth Creek Preserve in western Washington.
Assisted population migration involves moving the seeds of a native species, and therefore its genes, within its current growing range.
In contrast, assisted species migration involves moving species well outside their current range, such as bringing redwoods and sequoias into Washington.
A third type of assisted migration, called “range expansion,” involves moving a species slightly beyond its current growing range.
Case’s project involves testing whether breeds of native Douglas fir and western hemlock from drier parts of the Pacific Northwest can be used to help western Washington forests adapt to climate change. He says the Nature Conservancy is focusing on population migration because it has fewer ecological risks.
“Whenever you put something in an area that’s not available locally you increase the risk of failure,” Case said. “You increase the risk of disrupting potential ecosystem functions and processes.”
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EDITOR’S NOTE: This story is part of a collaboration between The Associated Press and Columbia Insight, investigating the impact of climate on trees in the Pacific Northwest.
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Population migration is the only type of assisted migration currently practiced by the Forestry Service throughout the country, according to Dr. David Lytle, the agency’s deputy head of research and development.
“We are very cautious and do not engage in long-distance movement and establishment of plant material outside the historical range of a species that is incompatible with it,” Lytle said.
The Forest Service is pursuing assisted population migration because it will have few “negative consequences” for ecosystems, he said.
Douglas Tallamy, a professor of entomology and wildlife ecology at the University of Delaware, said one potential negative consequence of species migration is the possibility that native caterpillars may not eat the leaves of migrating non-native species. As caterpillars feed on birds and other animals, this may cause disruption to the food web.
This could happen if the City of Portland moves an oak species from further south, Tallaght noted. “Oaks are the most important plant to support our wildlife in North America,” he said, “but when you move them out of range, the things that are adapted to eat them don’t have access to them. no more.”
The City of Portland’s Urban Forestry program is currently piloting the assisted migration of 11 tree species, including three southern oak species: California black oak, canon live oak and interior live oak.
When asked via email about possible ecological disruption, Portland City Forests & Urban Forestry Manager Jenn Cairo responded: “We use research from universities, state and federal sources, and the experience of field practitioners local and regional.”
Another advocate for species migration is the citizen-led Puget Sound-based Proliferation Nation. The organization has planted trees in various parks in the Seattle area and has the ambitious goal of bringing “one million coast redwoods and giant sequoias to the Northwest,” according to its website.
The PropagationNation website also recommends planting redwoods in areas where native western red cedar, western ruby, Sitka spruce and bigleaf maple already grow.
Western redcedar, western hemlock, and bigleaf maple have experienced a decline in mortality and growth in recent years due to climate.
Philip Stielstra, founder and president of PropagationNation, and a retired Boeing employee, declined to comment for this story.
David Milarch, founder of the Michigan-based Archangel Ancient Tree Archive, which supplied PropagationNation with redwoods and sequoias, says his trees are not intended to replace native species of the Pacific Northwest.
“All we’re doing is expanding the range (of the redwoods and sequoias) northwards in the hope that they’ll still be here in 100 to 200 years and not on the dying list expired,” said Milarch.
Robert Slesak, a research forester at the Pacific Northwest Research Station, runs the Forest Service’s Experimental Network for Assisted Migration and Based Forestry, or the ENAMES project, which oversees population migration sites in Washington, Oregon and California.
Slesak called redwoods moving north a “risk proposition.” He said he has serious concerns about assisted species migration and assisted migration efforts that lack experimental rigor.
“Large-scale assisted species migration without a lot of experimental results to guide it is very risky,” Slesak said. “Everyone knows that we need to take some kind of climate action, but the risk is that it will get worse.”
However, as the effects of climate change increase, public and private groups risk increasing acceptance across the Pacific Northwest.
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Nathan Gilles is a science writer and journalist based in Vancouver, Washington.
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Columbia Insight is an Oregon-based non-profit news website that covers environmental issues affecting the Pacific Northwest.
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Associated Press climate and environmental coverage is supported by several private foundations. See more about the AP climate initiative here. The AP is solely responsible for all matters.
