SNOW ABLATION MODELING IN A MATURE ASPEN STAND OF THE BOREAL FOREST

Snow ablation modelling at the stand scale must account for the variab ility in snow cover and the large variations of components of energy t ransfer at the forest floor. Our previous work successfully predicted snow ablation in a mature jack pine stand by using a one-dimensional s now process model and models predicting radiation below forest canopie s. This work represents a second test of our basic modelling scenario by predicting snow ablation in a leafless, deciduous aspen stand and v erifying the results with field data. New modifications to the snow mo del accounted for decreased albedo owing to radiation penetration thro ugh optically thin snowpacks. A provisional equation estimates litter fall on the snowpack, thereby reducing the areal averaged albedo. We s howed that subcanopy radiation measurements can be used with a canopy model to estimate a branch area index for defoliated aspen as an analo gue to the foliage area index used for conifers. Modelled incoming sol ar and long-wave radiation showed a strong correlation with measuremen ts, with r(2) = 0.95 and 0.91 for solar and long-wave radiation, respe ctively. Model results demonstrate that net radiation overwhelms turbu lent exchanges as the most significant driving force for snowmelt in a spen forests. Predicted snow ablation in the aspen stand compared very favourably with available data on snow depth. (C) 1998 John Wiley & S ons, Ltd.