White spruce and balsam fir colonisation of a site in the southeastern boreal forest as observed 68 years after fire

The goal of this study was to describe white spruce (Picea glauca (Moench) Voss) and balsam fir (Abies balsamea (L.) Mill.) recolonization in a forest destroyed in 1923 by an intense fire. Regeneration was evaluated considering both ecological site factors and distance to a seed source. Sampling was conducted along four transects crossing this stand. Each transect began in an unburned zone or at the edge of the intact forest and progressed towards the centre of the 1923 burn taking into account the two types of soil parent materials. Demographic variables of these two species were assessed by dating, using dendrochronology, at least 10 individuals found within each of the quadrats. The area and distance of the quadrats were determined as a function of the changes observed in stand structure and composition. As shown by its age distribution, fir recruitment was low during the first 30 years of succession but increased to higher levels thereafter. Colonization by white spruce is, on the other hand, characterized by two waves of recruitment, the first peak occurring during the initial phase of stand establishment and the second smaller peak occurring later during succession. The two factors found to have the greatest predictive power in determining the regeneration density of these two conifer species are the distance to the preserved zone, and hence to a seed source, and the type of soil parent material, as it determines the receptivity of the germination bed after fire. White spruce benefited from its ability to recolonize more rapidly than balsam fir by long distance reinvasion of the open site in the initial stage of succession. Balsam fir, on the other hand, recolonizes the site by advancing waves of regeneration in which groups of individuals are established at relatively short distances from parent trees. Although slower to recolonize, balsam fir demonstrates a greater ability for continued long-term recolonization. With respect to the ability to predict the pattern of natural regeneration abundance following fire, the results of this study demonstrate the importance of spatial distribution of seed sources and quality of germination beds as it varies with superficial deposit type. Therefore, these two components should be considered in models predicting forest succession following fire.