| The objectives of this study were to develop a forest biomass and nutrient cycling model, and to test this model with pre- and post-cutting field data from the Nashwaak Experimental Watershed Project (NEWP, which represents a mixed hardwood site in central New Brunswick), and field data from a jack pine (Pinus banksiana) stand near Chapleau in north-central Ontario. These data included information about nutrient concentrations in atmospheric deposition and in soil leachates, and ancillary information as required for model initialization. Ancillary information addressed forest cover type, stand density, soil rooting depth, forest floor depth, soil texture, soil substrate type, initial amounts of biomass and N, S, Ca, Mg, and K contents in foliage, wood, roots, initial mineral soil nutrient contents in soil solution, on ion-exchange sites, and in the soil overall.; The resulting model was tested with the pre- and post-harvest nutrient concentration data in the soil solutions for both forest sites. From these data, it was determined that post-harvest soil leaching had increased ∼5-fold for NO3-N, 80% for NH4-N, 71% for K, 20% for Ca, and 14% for Mg two years after the watershed-wide stem-only harvest operations at NEWP. For the tree-length harvesting on the jack pine sites, soil leaching increased ∼2.5-fold for NO3-N, 14% for NH4-N, 50% for K, and 14% for Mg three year after harvesting. For whole-tree harvesting on the jack pine site, soil leaching increases were relatively small with 11% for NO3-N, 13% for NH4-N, 9% for K, and 7% for Mg for the same time period. Thereafter, these increases further diminished to pre-harvest levels within 5 years or so. Post-harvest increases for Ca were negligible at both locations.; With the model, and through the related mass balance assessment, it was realized that current N and K supply for jack pine uptake would mainly be due to soil organic matter mineralization (83 and 66%, respectively). In contrast, the supply of Ca and Mg would mainly be due to soil mineral weathering (50 and 52%, respectively). Reducing the existing amounts of soil nutrient availabilities and forest floor organic matter accumulations on these sites through high harvesting intensities would likely result in a diminished and therefore non-sustainable nutrient supply situation.; The overall model formulation is consistent with general expectations regarding forest growth. The model may, therefore, be used to evaluate forest sustainability criteria and indicators that specifically deal with site-specific forest nutrient cycling and related nutrient availabilities within the context of sustainable forest harvesting, soil conservation and the evaluation of stream water quality. (Abstract shortened by UMI.)... |
