From the tree to the forest: the influence of a sparse canopy on stand scale snow water equivalent

The canopy of an individual tree has a negative effect on the accumulation of snow around tree boles, resulting in a decrease in snow depth inward from the edge of the canopy to the tree trunk. This influence of trees on snow distribution affects the total volume of water stored in the snowpack, especially for a sparse forest stand. However, snow measurements, in particular depth, are typically made between trees, and this neglects the decreased accumulation around trees. As well, little is known about changes in snowpack density under the canopy compared to between trees. Sparse individual trees have their own microclimate (energy balance, wind profiles, etc.) that could produce directional variations in snowpack properties. To establish how the decreased snow depth and possibly change in snowpack density under the canopy can affect estimates of stand scale SWE, depth and density measurements were taken in the four cardinal directions around three Picea engelmanii and two Abies lasiocarpa during the winters of 2005 and 2007 near Cameron Pass, northern Colorado. These near tree measurements were assessed against existing snow depth models and superimposed on a 50-m transect of depth measurements taken at 0.5-m intervals. Three scenarios of a sparse forest were considered: one tree with a 1-m canopy radius, one tree with a 2-m canopy radius, and three trees each with a 2-m canopy radius. Directionality was observed in the snow depth increasing away from each tree. An increasing trend in snowpack density was observed outward from each tree. The estimated average transect snow water equivalent decreased by 12.8 % with the addition of three trees with 2-m canopy radii