Low-snow freezes blamed for killing vast stands of culturally and economically important trees in Alaska
By Summit Voice
SUMMIT COUNTY — Forest Service scientists say huge Alaska tracts of yellow-cedar trees have been dying because their roots are freezing during cold weather in late winter and early spring, when there’s no snow to protect the roots.
Most climate models suggest that coastal Alaska will less snow but a persistence of periodic cold weather events in the future.
Yellow-cedar is a culturally and economically valuable tree in southeastern Alaska and adjacent parts of British Columbia. The slow-growing trees can reach 700 to 1,200 years in age. The tree has long been culturally significant to Native Alaskans who use it to make paddles, masks, dishes, and woven items. The wood is also very valuable commercially (for home and boat building) because of its straight grain, durability, and resistance to insects.
Yellow-cedar decline affects about 60 to 70 percent of trees in forests covering 600,000 acres in Alaska and British Columbia.
When snow covers the ground, it protects the shallow roots from extreme soil temperatures. The shallow rooting of yellow-cedar, early spring growth, and its unique vulnerability to freezing injury are all factors in the regional die-off.
A new paper from the U.S. Forest Service Pacific Northwest Research Station, “Shifting Climate, Altered Niche, and a Dynamic Conservation Strategy for Yellow-Cedar in the North Pacific Coastal Rainforest,” summarizes 30 years of research and offers a framework for a conservation strategy for yellow-cedar in Alaska.
- The complex cause of yellow-cedar decline is related to reduced snow, site and stand characteristics, shallow rooting, and the unique vulnerability of the roots to freezing in low temperatures.
- Low snow levels and poor soil drainage lead to impact root injury and the eventual death of yellow-cedar trees. The tree thrives in wet soils, but its tendency to produce shallow roots to access nitrogen on these sites made it more vulnerable when spring snow levels were reduced by climate warming.
- Yellow-cedar health depends on changing snow patterns, thus locations for appropriate conservation and management activities need to follow the shifting snow patterns on the landscape.
- Some responses to shifting climate are expected to be complex and difficult to anticipate. Long-term multidisciplinary research was needed to determine the true role of climate in the health of yellow-cedar and untangle it from other processes and natural cycles in forests.
Scientists are working with partners in the Alaska Region of the Forest Service to use this new information as the framework for a comprehensive conservation strategy for yellow-cedar in Alaska in the context of a changing climate.
“We also have ongoing projects with colleagues in the Tongass National Forest in Alaska on planting and thinning to favor yellow-cedar on suitable habitat,” adds co-lead author and station scientist Dave D’Amore, “especially on well-drained productive soils where most of the commercial forestry exits.
Silvicultural techniques can be used to nudge the ecological niche of yellow-cedar, making it more competitive on these favorable sites.”
Other coauthors of the synthesis are Paul Schaberg, U.S. Forest Service, Northern Research Station; Dustin Wittwer, U.S. Forest Service, Alaska Region; and Colin Shanley, The Nature Conservancy. Read the paper online at http://www.aibs.org/bioscience/current_issue.html.