Snow not falling on cedars

 

I remember the moment when, drinking strong coffee under a tin roof pattering with the relentless southeast Alaska rain, I first cut yellow-cedar with a chisel. A clean curl of cream-colored, sharp-scented wood peeled from the big beam. My patient teacher, whose whole house was built from the stuff, just grinned through his bushy beard at my astonishment. It was the finest wood I'd ever worked.

During my weeks hanging around Petersburg, Alaska, a fishing town that clings to the narrow shoreline of a big forested island, I don't remember seeing many dead yellow-cedar except the one I helped haul out of the woods. That giant old tree had a ten-foot butt-end that four of us spent the day winching from below the dirt road and getting onto the flatbed trailer, which it filled. But dead yellow-cedar were out there. They'd been dying in great numbers for at least a century along nearly a thousand square miles of northern Pacific coast.

Until recently, the cause of the tree's decline was unknown. Starting in the 1980s, researchers searched unsuccessfully for a killer fungus or virus. It wasn't until a couple years ago that a handful of studies concluded that the culprit is climate change. The story fits superficially into the rallying cry against global warming, but the reality is more complex. “Climate change,” as used in the studies, doesn’t refer to human-caused global warming, but natural fluctuations in climate that occurred in the pre-industrialized era. Cedars started dying well before we began pumping tons of CO2 into the atmosphere, but the effects are still being felt now. 

Yellow-cedar inhabits coastal foothills in the Pacific Northwest and Alaska where the winter weather swings between rain and snow. The tree depends on snow to insulate its shallow roots, which are more vulnerable to freezing than those of other species. So during a period of relatively cooler weather known as the Little Ice Age, roughly between 1000 and 1800, yellow-cedar thrived and expanded its range. During this period, temperatures were perhaps half a degree cooler across the northern hemisphere, with local variations. Parts of central Alaska may have been as much as three degrees colder. Snow piled up and glaciers plowed down the valleys.

Then, around 1800, the climate began to warm. Scientists still speculate why (solar cycles, volcanoes, and ocean currents are possibilities), but the effects are undeniable. Alaska's coastal glaciers thinned and retreated so much that the unburdened land rebounded nearly 20 feet in some places. This warming coincides with the bulk of the yellow-cedar decline, which occurred between 1880 and 1900.

"It's ironic that a species might be dying due to freeze-induced mortality when the climate signal is warming," Paul Schaberg, a Forest Service plant pathologist who co-authored one of the recent studies, told The Associated Press. But warmer winters have meant less snow, especially in lower elevations, leaving yellow-cedar roots exposed to arctic cold snaps that descend from interior Canada. The accumulating stress of these root-freezing events has slowly killed yellow-cedar off in much of its range. A string of warm winters in the late 1970s and early '80s produced another wave of die-off.

Yellow-cedar in West Chichagof-Yakobi Wilderness Area. Photo courtesy Paul Hennon, USFS.

Although researchers attribute the yellow-cedar's past troubles to natural warming, they say human-caused warming will stress the species further. The Intergovernmental Panel of Climate Change predicts that even a "low-emissions scenario" will warm southeast Alaska by four to five degrees by century's end, or seven degrees in a "high-emissions scenario." Such warming will reduce snowfall even more, but probably won't be enough to stave off the arctic cold snaps that kill the trees.

Now the Forest Service is trying to help the species adapt. This summer, the agency will plant 70,000 yellow-cedar on Prince of Wales Island, not far from Petersburg. Crews will plant the trees on higher, north-facing slopes more likely to hold snow, and in pockets of deeper, drier soils where their roots are less prone to freezing. And they'll give the trees a leg-up against another enemy, deer (who love to munch on the tender saplings), by planting later in the season when other plants are leafed out, and by ringing the trees with protective tubes and spraying them with bloodmeal.

Meanwhile, cedar die-offs have slowed since the 70s and 80s, and "there are areas where the cedars, at least for the time being, are doing really well," says Paul Hennon, a research forest pathologist with the Forest Service in Juneau, Alaska who has studied yellow-cedar for over two decades.

"We don't see really losing cedar (totally)," says Hennon. "It has a wide enough niche ... it's going to be doing okay for a while."

Marshall Swearingen is a High Country News intern.

Upper image courtesy flickr user cyborgsuzy.

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