SNOW-INDUCED THERMAL VARIATIONS AROUND A SINGLE CONIFER TREE

The influence of trees on the ground thermal regime is important to th e overall winter energy exchange in a snow-covered, forested watershed . In this work, spatial zones around a single conifer tree were define d and examined for their controls on the snow cover, snow-ground inter face temperatures and frozen ground extent. A large white spruce (Pice a glauca), approximately 18 m tall with a crown diameter of 7.5 m and located in northern Vermont, was the subject of this study. The tree w as instrumented with thermistors to measure the snow-ground interface temperature between the tree trunk and 6 m from the tree into undistur bed snow. Four distinct zones around the conifer are defined that affe ct the snow distribution characteristics: adjacent to the trunk; the t ree well; the tree crown perimeter; and the unaffected area away from the tree. At the time of peak snow accumulation and during the ablatio n season, snow depth and density profiles were measured. The area bene ath the canopy accumulated 34% of the snow accumulated in the undistur bed zone. By the end of the ablation season, the depth of snow under t he canopy had decreased to 18% of the undisturbed snow depth. The tree and branch characteristics of spruce in this temperate climate result ed in a different snow depth profile compared with previous empirical relationships around a single conifer. A new relationship is presented for snow distribution around conifer trees that has the ability to be tter fit data from a variety of conifer types than previously publishe d relationships. Less snow beneath the canopy led to colder snow-groun d interface temperatures than measured in undisturbed snow. The depth of frozen ground in the different zones was modelled using a simple an alytical solution that showed deeper frost penetration in the tree wel l than beneath the undisturbed snow.