Moderate-severity disturbance dynamics in Abies balsamea-Betula spp. forests: The relative importance of disturbance type and local stand and site characteristics on woody vegetation response

Sudden versus gradual mortality of canopy trees can differentially affect relative species assemblages after disturbance, although local biotic and abiotic habitat characteristics can modify expected patterns. Woody vegetation responses to moderate-severity disturbances were characterized and compared in relation to pre- and post-disturbance stand and site characteristics within Abies balsamea-Betula spp. stands of southeastern Quebec, Canada. Disturbances were caused by gradual mortality due to the spruce budworm (Choristoneura fumiferana), sudden mortality due to windthrow, or a combination of both. Redundancy Analysis with forward selection was used to rank the importance of disturbance type and local stand and site characteristic variables on species regeneration patterns. In order of decreasing importance, stand composition prior to disturbance, density of coarse woody debris, slope, distance to nearest conifer stand, density of deciduous legacy trees, spruce budworm disturbance, and soil drainage were important in determining post-disturbance species composition. No distinct regeneration patterns were associated with windthrow or interaction disturbance types. Although moderate-severity disturbances affected species distribution, local biotic and abiotic stand and site characteristics, particularly pre-disturbance stand composition and density of coarse woody debris, were more important in determining post-disturbance species distribution patterns.