The Radiation Budget of a Subarctic Woodland Canopy

Abstract

Open woodland is a major sub-type of the circum global boreal forest zone. In Canada it dominates the basins of a number of large hydroelectric schemes in which snowmelt is a critical phase of the hydrologic cycle. The forest vegetation strongly influences the radiant energy flux to the snow and is therefore important in the production of snowmelt runoff and its prediction. The radiation budget of a subarctic open woodland canopy in northern Quebec is computed from measurements of net allwave, solar and longwave radiation components over the snowpack at treeless and woodland sites. The canopy gains solar radiation both directly and from solar radiation reflected off the snowpack, the latter enhanced by the larger spacing between tree crowns. Canopy heating from absorbed solar radiation leads to a considerable longwave flux being emitted by the tree crowns. Overall, the radiant energy exchange in the open woodland behaves differently than for a closed crown forest. This is believed to be a function of a variety of canopy characteristics, not solely of tree crown density.

Key Words: snowmelt, open woodland, radiation budget, northern Quebec