One Way to Save Struggling Trees: Help Them Migrate

As native trees in the Pacific Northwest die off due to climate changes, the US Forest Service, the city of Portland, 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 predicted to move farther north and higher in elevation. Of course, trees can't get up and walk to their new climatic homes. This is where assisted migration is supposed to lend a hand, the AP reports. 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.

Not everyone agrees on what type 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 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 is a huge difference between assisted population migration and assisted species migration," said Michael Case, forest ecologist at the Virginia-based Nature Conservancy, who runs an assisted population migration experiment at the Conservancy's Ellsworth Creek Preserve in western Washington. The terms:

• Assisted population migration involves moving a native species' seeds, and by extension its genes, within its current growing range.
• By contrast, assisted species migration involves moving a species well outside its existing range, such as introducing redwoods and sequoias to Washington.
• A third form of assisted migration, range expansion, amounts to moving a species just beyond its current growing range.

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Case says the Nature Conservancy is focusing on population migration because it has fewer ecological risks. "Whenever you plant something in an area where it is not locally found you increase the risk of failure," Case says. "You increase the risk of disturbing potential ecosystem functions and processes." Population migration also is the only form of assisted migration practiced nationwide by the Forest Service. Read the full story, which has details on the differing approaches.

(More climate change stories.)