Yellow-cedar in decline. Credit: Paul E. Hennon/USFS/

For the better pa rt of the last century, swaths of yellow-cedar trees have been dying. The phenomenon, called yellow-cedar decline, has affected more than 60 percent of trees in a 600,000-acre region stretching across Alaska and British Columbia. Despite years of research, scientists were unable to find the cause of the massive die-offs. Now, scientists at the USDA Forest Service’s Pacific Northwest Research Station have found that the decline in yellow-cedar can be attributed to root freezing, a problem that stems from a lack of snow.

When a layer of snow covers the ground, trees’ roots are insulated from exceptionally cold temperatures. Yellow-cedar trees have shallower root systems than many other species, particularly in early spring when smaller, new roots begin to grow, so they are exceptionally vulnerable to root freezing. The species’ preference for wetter soils does not help matters, as that type of habitat, when left without an insulating layer of snow, can freeze solid and turn deadly for the tree’s roots.

The research, published in the February issue of BioScience, is the result of 30 years dedicated to studying the phenomenon. Now, foresters finally have an answer to a mystery that has been plaguing the region for decades, but a new issue presents itself: how to go about restoring the species. With the trees so dependent on snow and climate patterns continuing to change, it is difficult to predict where the yellow-cedar could thrive. However, knowing what factors are threatening the tree gives foresters and scientists a chance to create a new template for species restoration, which may be useful as more species susceptible to these types of changes continue to feel the effects of a changing climate.