Effects of fire severity on early development of understory vegetation

Abstract

Four boreal mixedwood stands burned by the 1999 Black River wildfire in southeastern Manitoba were sampled to examine the effects of fire severity on early regeneration dynamics of understory vegetation. In each stand, three fire severity classes (scorched, lightly burned, and severely burned) were identified based on the degree of forest floor consumption, and six plots per severity class were randomly selected. Variation in fire severity significantly affected the initial regeneration of the understory plant community. Regeneration response after fire was largely controlled by interactions between fire severity and species' regeneration strategy. Establishment of invaders, seed bankers, and sprouters was best on severely burned, lightly burned, and scorched plots, respectively. Species richness and Shannon's diversity index was reduced by severe fire only in the first postfire year. However, the effects of fire severity on species abundance and composition persisted through the entire study period (1999–2002). Rapid changes in the understory plant community were only observed during the initial 3 postfire years, regardless of fire severity. At the end of the study, herbaceous plants were the most dominant component, with woody plants being a codominant component on scorched plots, and nonvascular plants being a codominant component on severely burned plots.