Boreal forest disturbance and streamflow response, northeastern Ontario

The effects of forest disturbance on streamflow from small (<10 km(2)) basins have been well documented; however, implications of such disturbance for streamflow from relatively large rivers in the Canadian boreal forest are unclear. Landsat imagery was used to determine changes in the type, amount, and location of forest disturbance in northeastern Ontario between 1985 and 1990. These were compared with streamflow responses from medium- and large-scale basins in the region. Harvesting dominated forest disturbance, and total disturbance as of 1990 ranged from 25% of basin area in the northwest part of the region to 5% in the southeast. There was Limited streamflow response to land cover changes, with no definitive changes in water year runoff or peak flow magnitude and timing. This likely reflects the ability of relatively large basins to buffer the hydrologic impacts of the small degree of recent forest disturbance, combined with the influence of climatic variability on temporal trends in basin streamflow. However, disturbance was associated with increases in moderate and low flows from medium and large basins, respectively, which occurred largely during summer months.