Petersburg Pilot

Light snow pack may

translate to cedar tree die-off

February 4 , 2010.

Inspired by the data collection in Petersburg, which began in the early 1980s, US Forest Service soil scientist Jackie DeMontigny explained that measuring the snow pack on Wrangell Island was critical in developing a long-term set of data to use as a basis for research on snow level changes.

The lack of snow could very well be the cause behind the die-off of yellow cedar in the Tongass National Forest. USFS Research Plant Pathologist Peter Hennon has been studying the die off of yellow cedar. After chasing various theories, he found a direct correlation between snow pack and cedar death. “We’ve been comparing where cedar is dying and where its alive with patterns of snow [on Mount Edgecumbe], and that has turned out to be a pretty close association of cedar dying in areas that have the lowest snow pack.” Hennon cited various other studies pointing to the same conclusion.

The snow works as an insulator layer, keeping soil temperature just above freezing, regardless of the air temperature. The late winter/early spring cold snap damages the roots of cedars in areas with little-to-no snow, noted Hennon. As temperatures warm, cedars de-harden, making them more vulnerable to cold. What’s seemed to be the problem was that despite warmer weather in the season, the cold snap which drifted up from British Columbia continued to occur on a regular basis.

A study done by students at the University of Fairbanks found that most of the old-growth cedars established themselves in the canopy layers during the end of the little ice-age in the late 1800s. As climate data continues to predict warmer mid-winter seasons with consistent late winter cold-snaps, cedar die-off will continue to creep higher in elevation.

This year has been one of unusually warm weather, noted DeMontigny, who had travelled the trail in December to gather a monthly sample. Waterfalls that were frozen just a few weeks ago were running freely, and the snowshoes attached to her pack seemed almost excessive until the first remnants of snow begin appearing at around 1000 feet.

The first sample site, located at 500 feet was bare, with a touch of ice in the muskeg pools. At the second site, 1320 feet, snow conditions were similar to springtime. The snow had clearly been melting slowly and freezing overnight, giving the top a hard crust.

The samples, which were weighed and measured in depth, will be added to a collection of data meant to develop a base line for measuring snow changes as affected by current climate change.

Petersburg, Juneau, and Ketchikan have data that can be used as part of a model that looks at topography, snow depth, and other information to try and predict future snow patterns and cedar die off.

Hennson noted that future projections look bleak for yellow cedar, and a silvicultural effort to determine the best place to replant yellow cedar points to sites with good soil drainage and shading, and providing more stable soil temperatures, deeper root growth.