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Native trees are dying off in the Pacific Northwest due to climate changes, so it’s time for a new climate adaptation strategy called “assisted migration.” The U.S. Forest Service, Portland, Oregon, and citizen groups around Puget Sound have embraced this deceptively simple idea.
As our world’s climate warms, tree growing ranges in the Northern Hemisphere are predicted to move farther north and higher in elevation.
But trees can’t move on their own. Enter assisted migration.
The goal is for humans to help trees keep up with climate change by moving them to more favorable ecosystems faster than they could migrate on their own.
However, there’s some debate on what type of assisted migration is best for the region and if it’s always a good thing.
There’s a divide between groups advocating for assisted migration to help struggling native trees and others who are concerned that native species might be replaced by trees from the south, like coast redwoods and giant sequoias.
“There is a huge difference between assisted population migration and assisted species migration,” said Michael Case, forest ecologist at the Virginia-based Nature Conservancy.
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.
“Whenever you plant something in an area where it is not locally found you increase the risk of failure,” Case said. “You increase the risk of disturbing potential ecosystem functions and processes.”
Population migration is the only form of assisted migration currently practiced nationwide by the Forest Service, according to Dr. David Lytle, the agency’s deputy chief for research and development.
“We are very, very cautious and do not engage in the long-distance movement and establishment of plant material outside and disjunct from the historic range of a species,” said Lytle.
The Forest Service is pursing assisted population migration because it’s likely to have few if any “negative consequences” to ecosystems, he said.
Douglas Tallamy, 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 might not eat the leaves of migrated nonnative tree species.