Sprucing up the mixedwoods: Growth response of white spruce (Picea glauca) to partial cutting in the eastern Canadian boreal forest.
Jessica Smith, Brian Harvey, Ahmed Koubaa, Marc Mazerolle.
Mixed species stands present a number of opportunities and challenges to forest managers. Boreal mixedwood stands in eastern Canada are often characterized by a canopy of shade intolerant aspen (Populus tremuloides) with more shade tolerant conifers in the sub-canopy layers. Because the aspen and conifers often attain optimal merchantable sizes at different moments, there is an interest in developing silvicultural practices toremoval of aspen and favour accelerated growth of residual conifers. We tested three partial harvesting treatments in mixed aspen - white spruce (Picea glauca) stands in which different proportions of aspen (0, 50, 65 and 100% basal area) were removed. Ten years after treatments, 72 spruce stems destructively sampled for stem analysis. Using linear mixed effect models, we analyzed growth as a function of treatment intensity, time since treatment, social status, pre-treatment growth rate, and neighbourhood competition. Relative to control stands, radial and volume growth responses were detected only in the extreme treatment of 100% aspen removal. In relative terms, suppressed trees showed the greatest magnitude of cumulative growth increase. Growth response was proportional to pre-treatment growth rate and, among neighbouring trees, only coniferous neighbours had a negative effect on white spruce growth.