Stand-level effects of soil burn severity on postfire regeneration in a recently burned black spruce forest

Abstract

This study tested whether variations in soil burn severity (soil organic layer consumption) influenced patterns of early postfire plant regeneration in a black spruce (Picea mariana (Mill.) BSP) forest in interior Alaska. Variations in burn severity were related to measurements of postfire tree seedling establishment and cover of plant growth forms observed 7–8 years after fire. Black spruce and trembling aspen (Populus tremuloides Michx.) showed significant and opposite responses of seedling density to changes in soil burn severity. Positive correlations between burn severity and aspen density and individual seedling biomass led to an increase of over three orders of magnitude in aspen standing biomass (aboveground, g/m2) from the least to most severely burned sites. Variations in aspen productivity and consequent effects on litter production and seedbed quality possibly explain the observed negative response of black spruce density to increasing burn severity. Variations in the cover of several plant growth forms were also strongly correlated with patterns of soil burn severity. Regenerating plant communities in low-severity sites had a greater cover of evergreen shrubs and graminoids, while high-severity sites had increased cover of aspen and acro carp ous mosses. Observations of regeneration patterns in the burn are largely consistent with experimental studies of severity effects and suggest that variations in soil burn severity can have a strong influence on landscape patterns of postfire forest recovery. In this case, increases in burn severity have shifted successional trajectories away from simple conifer self-replacement towards a trajectory of mixed conifer and deciduous dominance.