Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The introduction of logging associated with the industrial era (since ∼1900) has modified the natural disturbance regime of the world's boreal forests. The object of this study was to document, using forestry maps prepared in 1950 and 2005 from air photos, the dynamics of high-elevation boreal forest landscapes affected by 20th century logging and natural stand-replacing disturbances. In 1950, the majority of forests in the study area were unlogged (>88%) and dominated by old conifers (≥81. years of age), predominantly balsam fir and black spruce. Logging activities affected 76.2% of the study area at least once between 1930 and 2005. Forests located at lower altitudes (710-880. m) were more intensively logged than those of higher altitudes (880-1050. m). The present-day forest landscape, in contrast to that of 1950, is fragmented and dominated by younger stands. The sectors that have been logged at least once have experienced more forest cover changes relative to undisturbed areas. The 2005 cover composition was relatively similar to that observed on 1950 maps. In the 20th century, natural stand-replacing disturbances were infrequent and had a less extensive effect on the forest landscape than did logging. The fire rotation in the 20th century was more than 3000. years, with the overall stand-replacing natural disturbance rotation approaching 800. years. Our study suggests, at least in the 20th century, that canopy gaps and small-scale windthrows seem to be the principal factors controlling high-altitude natural forest dynamics and that natural stand-replacing disturbances were of little consequence. Twentieth century forestry practices were the most important driving force explaining the present-day age structure of the forest landscape. Ecosystem-based management strategies for high-elevation boreal forests should take this into consideration, and implement silvicultural practices that mimic the natural disturbance regime more closely. We therefore suggest the adoption of strategies that favor partial cuts.