Effects of Forest Harvesting on Carbon and Nitrogen Levels in Soils and Stream Sediments in Northwestern Ontario
Boreal forest soil biogeochemical activities are changing in light of ecosystem disturbance and other impacts. Soil carbon and nitrogen, for example, are important for soil health, forest regeneration following harvest or fire, and for sequestration of greenhouse gases. Our understanding of how forest harvesting and other silvicultural activities impact losses of carbon and nitrogen from soils is limited however. This study was conducted to observe the effects of forest harvesting on carbon and nitrogen concentrations and ratios in soils and stream sediments in northwestern Ontario. Various soil samples were collected from two watershed clusters during the late summer months of 2019-2021, in a broader region surrounding the town of Dryden, Ontario. Sampling was focused on different habitats including stream sediment, riparian soil, wetland soil and upland soil and included time periods before harvest, after harvest, and in areas not subject to harvest (reference areas). In general, stream sediment carbon and nitrogen concentrations significantly increased post-harvest in two of the most disturbed watersheds, but C/N ratios did not significantly change. Post-harvest, carbon and nitrogen content tended to decline in riparian soils, whereas results in wetland and upland soils were variable through time and most likely represented small-scale spatial variability in sampling. Ongoing work will examine these changes in relation to organic carbon and nitrogen content in streamwater draining these same areas. Overall, the results from this study may help to identify issues with current forest management practices and identify potential alternative approaches to maintain soil health.