Boreal forest disturbance and streamflow response, northeastern Ontario

The effects of forest disturbance on streamflow from small (<10 km(2)) basi ns 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 an d 1990. These were compared with streamflow responses from medium- and larg e-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 re sponse to land cover changes, with no definitive changes in water year runo ff or peak flow magnitude and timing. This likely reflects the ability of r elatively large basins to buffer the hydrologic impacts of the small degree of recent forest disturbance, combined with the influence of climatic vari ability on temporal trends in basin streamflow. However, disturbance was as sociated with increases in moderate and low flows from medium and large bas ins, respectively, which occurred largely during summer months.