Yellow-cedar, a culturally and economically valuable tree in southeastern Alaska and adjacent parts of British Columbia, has been dying off across large expanses of these areas for the past 100 years. But no one could say why. “The cause of tree death, called yellow-cedar decline, is now known to be a form of root freezing that occurs during cold weather in late winter and early spring, but only when snow is not present on the ground,” explains Pacific Northwest Research Station scientist Paul Hennon, co-lead of a synthesis paper recently published in the February issue of the journal BioScience. “When present, snow protects the fine, shallow roots from extreme soil temperatures. The shallow rooting of yellow-cedar, early spring growth, and its unique vulnerability to freezing injury also contribute to this problem.”