by PORTLAND, Ore. (AP) —
As native trees in the Pacific Northwest die off due to climate changes, 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 global climate warms, tree growing areas in the Northern Hemisphere are predicted to shift further north and to higher elevations.
Trees, of course, can’t just get up and walk to their new climatic homes. This is where assisted migration is supposed to help.
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 is always a good thing.
In the Pacific Northwest, a split has emerged between groups advocating for assisted migration that would help struggling native trees, and one that could instead see native species replaced on the landscape by trees from the south, including coast redwoods and giant sequoias.
“There’s a huge difference between assisted migration of populations and assisted migration of species,” said Michael Case, a forest ecologist with the Virginia-based Nature Conservancy.
Case is currently leading an assisted population migration experiment on the Conservancy’s Ellsworth Creek Reserve in western Washington.
Assisted population migration involves moving the seeds of a native species, and by extension its genes, within its current growing area.
In contrast, assisted species migration involves moving a species far beyond its current range, such as the introduction of redwoods and sequoias to Washington.
A third form of assisted migration, called “range expansion,” amounts to moving a species slightly beyond its current range.
Case’s project involves testing whether native breeds of Douglas fir and western hemlock from drier parts of the Pacific Northwest can be used to help western Washington forests adapt to climate change. She says the Nature Conservancy is focusing on population migration because it has fewer ecological risks.
“Any time you plant something in an area where it’s not found locally, the risk of failure increases,” Case said. “The risk of altering possible ecosystem functions and processes is increased.”
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EDITOR’S NOTE: This story is part of a collaboration between The Associated Press and Columbia Insight, exploring the impact of climate on trees in the Pacific Northwest.
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Population migration is the only form of assisted migration currently practiced by the Forest Service nationwide, according to Dr. David Lytle, the agency’s deputy director of research and development.
“We are very, very cautious and do not engage in long-distance movement or establishment of plant material outside and outside of a species’ historical range,” Lytle said.
The Forest Service is pursuing assisted migration of the population because it is likely to have few or no “negative consequences” for ecosystems, he said.
Douglas Tallamy, professor of entomology and wildlife ecology at the University of Delaware, said one possible negative consequence of species migration is the possibility that native caterpillars will not eat the leaves of migrated non-native tree species. Because caterpillars feed birds and other animals, this could cause disruptions to the food web.
This could happen if the city of Portland migrates oak species from southern locations, Tallamy said. “Oak trees are the most important wildlife-supporting plant we have in North America,” she said, “but when you take them out of reach, the things that are adapted to eating them no longer have access to them.”
The City of Portland’s Urban Forestry program is currently experimenting with assisted migration of 11 tree species, including three species of southern oaks: California black oak, canyon live oak, and interior live oak.
When asked by email about possible ecological alterations, Jenn Cairo, urban forestry and forestry manager for the city of Portland, responded: “We use research from universities, state and federal sources, and the expertise of local and regional field professionals.” .
Another advocate for species migration is citizen-led PropagationNation, based in Puget Sound. The organization has planted trees in several Seattle-area parks 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 hemlock, Sitka spruce, and bigleaf maple already grow.
Western red cedar, western hemlock and bigleaf maple have experienced weather-related die-offs and growth declines in recent years.
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 has supplied PropagationNation with redwoods and redwoods, says his trees are not intended to replace species native to the Pacific Northwest.
“All we’re doing is expanding the distribution (of sequoias and redwoods) northward in the hope that they will still be here in 100 to 200 years and not join the list of trees that are going extinct,” Milarch said.
Robert Slesak, a forestry researcher at the Pacific Northwest Research Station, directs the Forest Service’s Experimental Network for Assisted Migration and Settlement Forestry, or ENAMES project, which monitors population migration sites in Washington, Oregon and California .
Slesak called moving the redwoods north a “risky proposition.” He said he has serious concerns about both assisted migration of species and assisted migration efforts that lack experimental rigor.
“Widespread migration of assisted species without many experimental results to guide it is risky,” Slesak said. “Everyone knows we need to take some kind of climate action, but there is a real risk of making it worse.”
However, with the effects of climate change increasing, it is a risk that more and more public and private groups are taking on 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 nonprofit news website covering environmental issues affecting the Pacific Northwest.
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The Associated Press’ climate and environmental coverage is supported by several private foundations. See more about AP’s climate initiative here. The AP is solely responsible for all content.
