Shoreline forest disturbance rates in natural and managed forests of northwestern Ontario

Abstract

The purpose of this study was to compare the rates of disturbance along forested shorelines between natural and managed forests of the mesic boreal region of northwestern Ontario. Comparisons were made between areas that experienced wildfire bums versus areas that were subjected to existing forest management reserve policies. A shoreline forest is the area of an upland forest region located adjacent to, and influenced to varying degrees, by aquatic and/or riparian environments. Since these areas have unique biotic and abiotic characteristics and serve important ecological functions, they may be more sensitive than upland areas to forest harvesting and fire suppression. Fire is an important factor for maintaining the unique habitat of shoreline areas, therefore, shoreline area management that differs from the natural disturbance regime may cause unexpected and unwanted consequences. Shoreline forest disturbance rates were analyzed within disturbance events and watersheds using a variable width shoreline buffer to delineate the shoreline forest region. A disturbance event is a spatially aggregated and delineated collection of bum or harvest patches, whereas a watershed is an area of land within which all waters flow to a single river system. Remote sensing and geographical information systems technologies were applied to obtain new information about natural and artificial rates of forest disturbance. The band 5 subtraction change detection technique was 92% accurate in detecting forest disturbance patches from Landsat 5 and 7 Thematic Mapper satellite images. Our results show that shorelines are disturbed by both fire and harvesting at a lower rate than the surrounding landscape, but that the magnitude of this difference depends on the analysis unit. The disturbance rate variability of harvested watersheds was much greater than that of their associated shoreline forests, indicating that shoreline areas are treated more uniformly than the watershed as a whole. The rate of disturbance within harvest events was both lower and more variable than the rate of disturbance within fire events and the rate of disturbance for burned watersheds and associated shorelines was not consistent across spatial scales. If the goal of forest management is to better emulate natural disturbance patterns, disturbance patches within harvest events or watersheds should be more aggregated and the disturbance rates within shoreline forests should be increased to slightly below the watershed disturbance rates.