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CLIMATE WARMING, REDUCED SNOW, AND FREEZING INJURY COULD EXPLAIN THE DEMISE OF YELLOW-CEDAR IN SOUTHEAST ALASKA, USA

Yellow-cedar (Chamaecyparis nootkatensis) is a valuable tree species that has been experiencing concentrated mortality known as yellow-cedar decline on 200,000 ha of largely pristine forests in Southeast Alaska. Mature trees that regenerated and grew during the Little Ice Age have been dying on low elevation sites with wet soils and open canopies for about 100 years. We propose the following hypothesis to explain tree death (methods in parentheses): landscape features (digital elevation model via LiDAR) and soil properties (soil descriptions) produce poor drainage (wells and piezometers) which create open canopy forests (LiDAR and hemispherical photography) and shallow rooting; exposure allows soils to warm in early spring (air and soil temperature loggers) which triggers dehardening, the loss of cold tolerance, and eventual spring freezing injury (electrolyte leakage testing of tissues). The distribution of yellowcedar decline is associated with areas of low snowpack in winter and spring. Snow delays soil warming and presumably protects yellow-cedar roots through periods of spring frosts. Limited to higher elevations throughout most of its natural range, perhaps yellow-cedar migrated to lower elevations during the Little Ice Age, and these trees are now vulnerable to the lack of protective snow in these exposed, open canopy forests where forest decline is now severe.