Ecological impact of clear-cutting on black spruce-moss forests in southern Quebec

Clear-cutting has been the most common harvesting method used in the Canadian boreal forest during the past century. However, its impact on forest dynamics and environmental change remains largely unknown. In this paper we have examined the dynamics of black spruce-moss forests logged between the 1940s and the 1960s in the Parc des Grands-Jardins, southern Quebec. We have evaluated the potential of self-replacement of closed-crown forests 40 to 60 years after clear-cutting, and the interactions between tree harvesting, natural disturbances, and environmental factors. Clear-cutting can lead to the long-lasting opening of black spruce-moss forests. Several clear-cuts took place during or just after insect infestations. The spruce-moss forests regressed to shrub-moss woodlands showing little potential to revert to mature, pre-logged conditions. The main factors responsible for the shift to woodlands were the low density of advance growth, which was not compensated for by seedling establishment after the cut, and weak growth performance of black spruce. Stem growth slower than predicted for low site-class black spruce populations was likely caused by clumped distribution of layers, competition by dense ground vegetation, insect damage and reduction of site fertility after clear-cutting. The future of the post-logged woodlands relies heavily on the frequency and severity of natural disturbances that will certainly recur again in the area.