Abstract
Over the last three decades, the ecological basis for the generalized use of even-aged silviculture in boreal forests has been increasingly challenged. In boreal mixed-wood landscapes, the diminishing proportion of conifers, to the benefit of intolerant hardwoods, has been a primary concern, coupled with the general rarefication of old-growth conifer-dominated stands. In this context, partial cutting, extended rotations and forest renewal techniques that eliminate or reduce regenerating hardwoods have been proposed as means of regaining greater conifer cover. As a result, experimentation and industrial application of various forms of both variable retention and partial harvesting are occurring across the commercial Canadian boreal forest. In this study, we compared the effects of two harvesting intensities, clearcutting and low-intensity partial cutting (removal of 25–31% of tree basal area), on hardwood and conifer regeneration levels 7–19 years following treatments in aspen (Populus tremuloides)-dominated stands and verified whether regeneration differences existed between micro-sites on and off machinery trails. The abundance of aspen regeneration increased with percent basal area removal and was positively correlated to the abundance of mature aspen prior to harvesting. The abundance of fir (Abies balsamea) regeneration after partial cutting was similar to controls and higher than after clear-cutting and was positively correlated with ground cover of mixed litter (i.e., mixture of needles and leaves) and negatively correlated with ground cover of broadleaf litter. These results suggest that it is possible in boreal mixed-woods to control aspen abundance and promote or maintain conifer regeneration through silvicultural treatments that limit canopy opening and promote mixed forest floor litter.
Highlights
IntroductionMixed forests (i.e., forests comprised of a mixture of hardwood and softwood species) are an important ecological and economic component of the Canadian boreal forest [1]
Mixed forests are an important ecological and economic component of the Canadian boreal forest [1]
After harvesting, total and aspen BA were significantly higher in Cntrl stands than in stands treated with PC and CPRS, and significantly higher in PC stands than in CPRS
Summary
Mixed forests (i.e., forests comprised of a mixture of hardwood and softwood species) are an important ecological and economic component of the Canadian boreal forest [1]. Partial cuts could maintain stand structures and compositions, which are key habitat attributes for several plant and animal species in the boreal mixed-woods [11,12], similar to those resulting from natural secondary disturbances, such as insect outbreaks and windthrow [13,14,15], and alleviate the undesired effect of clear-cutting at the landscape scale. In many parts of the eastern boreal mixed-wood and continuous coniferous forests, the large-scale use of clear-cutting (in Quebec called cutting with protection of regeneration and soil, CPRS) and relatively short rotations (80–100 years) have led to a decrease in habitat and ecosystem diversity [16] and an increase in the relative proportion of pioneer, shade-intolerant hardwoods, especially trembling aspen [12,17]. The increase in the proportion of the territory dominated by trembling aspen, mainly due to its ability to regenerate by suckering, is indicative of the rejuvenation of the boreal mixed-woods [14,15]
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