Basing silviculture on natural ecosystem dynamics: An approach applied to the southern boreal mixedwood forest of Quebec

We present a method in which fundamental knowledge of natural ecosystem dynamics of the southern boreal forest may be used as a basis for a new silvicultural approach aimed at maintaining biodiversity and long-term ecosystem productivity under management. The natural disturbance regime of the southern boreal forest of Quebec is characterized by intense crown fires. Natural forest dynamics following fire on mesic sites involve a gradual replacement of stands of broadleaf species by mixedwood then softwood stands. This succession is accompanied by a decrease in soil fertility and in ecosystem productivity, In the absence of fire, spruce budworm outbreaks contribute in regenerating mature, fir-dominated forests and in reintroducing a hardwood component into stands. Current silvicultural practices promote successive rotations of similarly composed stands. Attaining softwood regeneration following harvest of softwood stands often necessitates site preparation, planting and control of competitive species, including economically and ecologically valuable hardwoods. Al the landscape level this strategy may contribute to decreasing stand diversity by favouring replacement of mixedwood stands by hardwood or softwood stands. Natural dynamics indicate that a silvicultural approach favouring species replacement while, at the landscape level preserving a representative proportion of hardwood, mixedwood and softwood stands would be more appropriate. The advantages of such an approach are discussed in comparison with current practices.