Effectiveness of delayed brush cutting and herbicide treatments for vegetation control in a seven-year-old jack pine plantation in northwestern Ontario, Canada

Abstract

Efficacy of three conifer release treatments, i) single application of glyphosate (Vision™) herbicide, ii) multiple application of glyphosate herbicide, and iii) motor-manual brush cutting for controlling competing plants, particularly trembling aspen (Populus tremuloides), pin cherry (Prunus pensylvanica), green alder (Alnus viridis spp. crispa), and beaked hazel (Corylus cornuta spp. cornuta), was studied in a seven-year-old jack pine (Pinus banksiana) plantation in northwestern Ontario, Canada. The single and multiple glyphosate applications were equally effective in controlling trembling aspen and pin cherry, causing over 90% stem mortality. The brushsaw treatment caused an initial decrease followed by an increase in stem density of these two species. A high degree of stem thinning by natural mortality in the untreated control plots was observed in trembling aspen (23–46%) and pin cherry (41–69%) over four years. As with trembling aspen and pin cherry, stem density of green alder and beaked hazel initially decreased and then increased following the brushsaw treatment, mainly due to resprouting. Stem mortality in green alder and beaked hazel was 45% and 97%, respectively, two years after the operational glyphosate treatment. Competition index (CI) was low (mean CI = 52, ranging from 18 to 115) in all the plots including the untreated control. There was a significant increase in basal diameter of jack pine in the brushsaw and herbicide-treated plots compared to the control three years after the treatments. Jack pine seedlings in the brushsaw and glyphosate treated plots were taller compared to that of control but differences were not significant. Lower species richness and diversity were recorded in the herbicide-treated plots compared to the brushsaw and control plots in the third growing season following treatment.