White spruce regeneration thirty-nine years post-fire in the boreal mixedwoods of Duck Mountain, Manitoba

Abstract

The effects of distance to seed source, biotic (vegetation cover) and abiotic (moisture and nutrients) factors on temporal and spatial patterns of white spruce dispersal, establishment and growth were examined at two sites, 39 years post-fire. Partial Mantel tests and partial regressions were used to determine factors affecting recruitment. A growth model, based on empirical results was developed to study growth suppression. A total of 2 042 white spruce trees were aged at the base, 938 of which were also aged at 1.25 m (breast height).The first cohorts to establish (ages 25-39) were affected very little by seed source proximity. Biotic factors such as birch, Corylus cornuta and moss cover were better able to predict abundance of earlier establishing white spruce. The second cohorts to establish (ages 5-24) were most affected by seed source proximity. Abiotic factors such as topographic complexity were also able to predict abundance of later establishing white spruce, in addition to biotic factors. Based on site comparisons it was concluded that Corylus cornuta and other deciduous vegetation limit white spruce recruitment through competition and shedding of broadleaf litter, and may suppress growth, especially of later establishing white spruce. Intraspecific competition between white spruce on these sites often leads to density-dependent mortality, in addition to growth suppression.