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Is this climate change-battered conifer migrating northward?

Scientists in Alaska are mapping what may be the tip of yellow cedar’s expanding range.

 

We are high in the fold of a steep, boggy valley when my friend Sarah spots our quarry tucked amidst blueberry and dark hemlocks. The first yellow cedar is spindly, no more than four inches in diameter, with striated reddish bark and drooping feathery fronds that seem to fit the sodden, misty September day. We poke around and find another, then another; there are a couple hundred of the trees in this stand, leaning over a cascading stream and spaced out along a hairpin bend in the trail that leads up to a Forest Service cabin above Juneau, Alaska.

A healthy yellow cedar in one of the expanding stands at the species' northern range edge, on Douglas Island near Juneau, Alaska.
Sarah Gilman

Young as they are, they look a bit scraggly to my untrained eye, but they’re a small bright spot in an otherwise dark story: Yellow cedar, a culturally and commercially important tree prized for its strong, remarkably decay-resistant wood, has died in droves thanks to long-term climatic shifts, and will likely lose much more as human-induced warming advances. And yet here, the trees seem to be thriving. Scientists studying this and 14 other scattered, isolated stands around Juneau believe they may represent a leading edge of the tree’s migration northward into more favorable climes. The researchers hope the trees will yield clues on how best to conserve the species as temperatures climb.

“One thing that seems to be coming out of the data is that these are new stands,” says disturbance ecologist Brian Buma, an assistant professor at University of Alaska Southeast who has been working on the project for three years. “There are not a lot of dead trees (in them), if any. They’re young — all less than 500 years old. And they seem to be expanding: The edges have some growth.”

Yellow cedars’ trials began in the late 1800s, around the time a cooling period called the Little Ice Age ended. Based on 30 years of research, scientists concluded in a comprehensive 2012 BioScience paper that, as snowpacks have thinned in the decades since, the trees’ shallow roots have had less insulation against cold snaps that still barrel in from the Arctic and the boreal forests of neighboring Canada, particularly in boggy areas where those roots tend to be even closer to the soil surface. In other words, even though natural climate cycles and our fossil-fuel guzzling ways have been driving temperatures higher, the trees have essentially been freezing to death. This April, the U.S. Fish and Wildlife Service even began mulling whether they warrant protection under the Endangered Species Act.

Seventy percent of mature yellow cedar are now dead in affected areas south of Juneau along a more than 600-mile swath of the tree’s mostly coastal range, which stretches from high elevation pockets in Oregon and Washington all the way to southern Alaska’s archipelagos and fjords. Because the trunks stand so long after death, says Paul Hennon, a Forest Service research plant pathologist and theBioScience study’s lead author, “people call them skeleton forests.”

A yellow cedar skeleton forest in the West Chichagof-Yakobi Wilderness, near the current northern edge of climate induced tree mortality.
Lauren E. Oakes

Over his years of studying the trees’ decline, Hennon also cataloged sightings people reported of healthy trees around Juneau, at the northeastern terminus of cedars’ range. Buma and masters student John Krapek compiled this information with other anecdotal reports, historical records, and surveys by local naturalists and set about finding the stands on the ground and mapping them. The search was “like a little treasure hunt,” Buma says, albeit one that occasionally involved brutal bushwhacks up steep cliffs over multiple days before a single tree could be confirmed. The researchers also noted the circumstances under which the trees grew, such as whether they were on north facing slopes. That data could help them locate other stands, as well as inform any future efforts to plant the tree in greater numbers at this more favorable margin of its range. Boosting cedars’ flight northward may ultimately be necessary for conserving the species: Though the trees do seem to be migrating, it’s at an Ent-like pace. “They’re maybe advancing at a rate of only 80 kilometers over several centuries,” says Buma. “That’s pretty pathetic. We hoped it would be faster. You know, you’re always kind of rooting for the little guys.”

And even though trees within the Juneau stands are growing quickly, there are few saplings in the mix with seedlings and bigger trees, says Krapek. That suggests something is stopping seedlings from growing toward maturity — possibly Sitka blacktailed deer, which favor them as a food source — perhaps slowing stands’ expansion.

Worse, evidence from elsewhere within the species’ northern range is less rosy. Stanford research associate Lauren Oakes found recent mortality along the coast of the West Chichagof-Yakobi Wilderness about 70 miles west of Juneau, and documented turnover of areas with heavy cedar mortality to western hemlock-dominated forests. She and Hennon also have a new study in Biological Conservation that shows trees north of those areas are beginning to display snowpack-related stress, too. It projects similar yellow cedar declines yet farther north in Glacier Bay National Park and Preserve, where stands are still healthy, based on climate models that take into account snowpack and soil drainage.

But a broader Forest Service snow modeling effort — part of a report that will be released in about a month — has left Hennon with some hope. Yes, some areas with healthy cedar stands will lose a lot of their snow over the coming decades, and thus a lot of their cedars. But “we expect that there are pretty sizeable areas where they’d remain healthy,” he says, particularly on the mountainous mainland right up against the Canadian border. “Even with reduced snow levels, our expectation is that there will still be enough snow to protect the cedars there. And those are highly protected landscapes with no timber harvesting.”

Sarah Gilman is a High Country News contributing editor based in Portland, Oregon. She tweets @Sarah_Gilman