In the warm wet Interior Douglas-fir biogeoclimatic subzone (IDFww), mechanical and herbicide site preparation and brushing treatments have been used to establish planted conifers. These silviculture treatments have been prescribed to control grass and shrub competition which rapidly develops after harvesting. Many of these sites, especially those with a southern aspect, have experienced poor survival of planted Douglas-fir. Poor plantation establishment has been attributed to poor stock quality and severe grass and shrub competition for soil moisture. Innovative brushing methods are needed for the establishment of Douglas-fir on these dry sites. Herbicide and mulch mat treatments have been used with some success.
Glyphosate herbicide has been widely applied in forestry as an effective vegetation control treatment. Hexazinone herbicide has also been used. Both herbicides have been shown to effectively control grass if applied while the grass is actively growing (Boyd et al. 1985; Fahlmann and Herring 1985). However, conifers are also very sensitive to herbicide application during the active growing period. Consequently, growing-season treatments must be applied either before conifer seedlings are planted (pre-plant application), before conifer growth begins, or the planted seedlings must be protected during application.
Research has suggested that the use of mulch mats can reduce grass and herbaceous competition for water and improve the initial survival and growth of conifer seedlings. Mulch mats are best applied during the spring, soon after planting, to avoid installation on top of the developing vegetation. The ideal silvicultural mulch mat should be opaque, dark, porous to permit water infiltration, able to retard evaporative water loss, supportive of favorable soil temperatures, sufficiently strong and durable to last until seedlings are established, low in cost and lightweight, non-toxic, and of a colour that blends into the landscape (McDonald and Helgerson 1990).
During 1993, a research trial was established to explore vegetation management options that may improve conifer survival and growth within the IDFww. The objectives of this study were to compare the effectiveness of the herbicides hexazinone and glyphosate and plastic mulch mat treatments for reducing grass competition and improving Douglas-fir seedling performance. Two separate experiments were established, representing dry and mesic environments within areas of homogenous terrain and vegetation.
This extension note summarizes the five-year results from these two experiments.
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Updated April 19, 2007