Early regeneration and growth dynamics of Populus tremuloides suckers in relation to fire severity

Four boreal mixedwood stands burned by the 1999 Black River wildfire in southeastern Manitoba were sampled to determine the effect of fire severity on density and diameter and height growth of trembling aspen (Populus tremuloides Michx.) suckers during the first three postfire years. Analysis of covariance, using prefire aspen basal area as the covariate, indicated that fire severity significantly affected postfire aspen sucker density, with significantly lower density found on severely burned plots. Changes in aspen sucker density over the three postfire years depended on fire severity, with significant changes observed only on scorched and lightly burned plots. Sucker mortality was positively related to the initial sucker density, with more than 80% of the total variance being explained. Fire severity significantly affected the growth of dominant aspen suckers in the first, but not the second and the third, postfire years. The first year of growth initially increased and then remained stable with the increase in density, while the second and third years of growth were not affected by density. Since fire severity within and (or) among burned stands is inherently heterogeneous, the effect of fire severity must be taken into account in predicting postfire density and growth of aspen suckers.