Effects of 20th‐century settlement fires on landscape structure and forest composition in eastern Quebec, Canada

Questions : Which role did historical anthropogenic disturbances play in modifying the natural fire regime? To what extent have they shaped current forest? Do those disturbances have lingering impacts in the present‐day landscape? Are certain tree species related to former land use? Location : eastern Quebec, Canada. Methods : Spatial data on landscape structure, burnt areas, settlements, and forest patches were vectorized on an archival map dating back to 1938. For each landscape class, the total area, the number of polygons, and the proportion of the total landscape occupied by the largest polygon were analyzed according to elevation and to the Euclidean distance from the "settlement" polygons. An index of the spatial link between the landscape classes was calculated, based on the proportions of the perimeter of the polygons of each class shared with each of the other classes. A Kolmogorov–Smirnov test for pooled data was used to obtain the frequency distributions of landscape classes as a function of distance. The association between settlement fires and present‐day vegetation, and more specifically Populus and Betula stands, was tested by superimposing the most recent ecoforest map on the 1938 land‐use map. Distance bands on either side of the 1938 settlement front were delineated to calculate the proportion of each distance class occupied by present‐day aspen and birch stands. Results : Anthropogenic fires generated a recognizable landscape pattern of land use. Burnt areas were mostly located within 2 km from a settlement. Most burnings observed on the 1938 map were human‐induced, based on their spatial connection with the settled areas. Lingering impacts of these 20th‐century fires on present‐day forests were identified using the peculiar spatial distribution of tree species. The presence and spatial distribution of aspen in the present‐day landscape is tightly associated with previously burnt areas. Conclusions : Past land‐use strongly altered the natural fires regime and associated tree species. Current land‐use could potentially lead to increased degraded forest landscapes in the near future. -- Keywords : anthropogenic fires, aspen, boreal forest, land use, North America, Populus, settlement, spatial landscape structure, temperate forest