Post logging succession and vegetation management with hexazinone herbicide in Picea glauca (Moench) Voss-Populus tremuloides Michx. forest

Abstract

The objectives were: to review the successional behaviour of white spruce (Picea glauca (Moench) Voss) - trembling aspen (Populus tremuloides Michxt) stands in the literature, to conduct field studies of the successional behaviour of planted white spruce in aspen stands, and to test hexazinone herbicide as a means of modifying the postlogging environment to release white spruce and other conifers. Five and 13 year old white spruce plantations were selected for study. Fifty square random plots were established in each plantation. Total and mean aspen and white spruce volumes per plot were calculated. Each plantation was stratified into 3 components or "Situation Types" based on aspen density. Five plots were established at both plantations in each of these Types. These "Situation Plots" were circular and selected so that a white spruce tree was located at each plot centre. The central white spruce and the mean aspen tree on each "Situation Plot" were cut down for stem analysis. The number of frost damaged tips per m[superscript 2] crown area on each central white spruce tree were calculated. The mean and total aspen volumes per plot are not related to the white spruce volumes per plot in either plantation. The current annual increment curves of the paired central white spruce and the mean aspen tree from each "Situation Plot" do not show any trends for the 5 year old plantation. Current annual volume increment curves from the 13 year old plantation show that a rapidly growing aspen tree will suppress its white spruce neighbour. The number of frost damaged tips per m [superscript 2] white spruce crown area significantly decreases as the number of aspen trees per plot increases at the 5 year old plantation. This relationship was not strong at the 13 year old plantation. This information is used to make recommendations for releasing white spruce from trembling aspen competition with hexazinone herbicide. Factorial herbicide trials were established in the field and greenhouse to evaluate the effect of hexazinone herbicide on white spruce and trembling aspen. Trials were also established to evaluate the effect of hexazinone on black spruce (Picea mariana (Mill.) B.S.P.), jack pine (Pinus banksiana Lamb.), willow (Salix spp.) and beaked hazel (Corylus cornuta Marsh.) , Various hexazinone rates, forms, spacings and spray positions were tested. Hexazinone 'Gridball' pellets and hexazinone concentrated solution (DPX-LX or LE) were the herbicide forms used. White spruce, black spruce and jack pine were found to be quite tolerant to hexazinone herbicide. Hexazinone did not reduce the survival or height growth of the white spruce significantly except in the greenhouse trial. Jack pine and black spruce were only significantly affected at the highest rates. In the greenhouse trial, the high hexazinone rates applied to the foliage and soil significantly reduced the survival and the foliage dry weight of both white spruce and jack pine. Most rates of hexazinone applied caused a significant reduction in height growth, survival and foliage dry weight of the aspen, willow and hazel. These results suggest that hexazinone can be used effectively to control weed species in conifer plantations.