Performance of planted spruce and natural regeneration after pre- and post-harvest spraying with glyphosate and partial cutting on an Ontario (Canada) boreal mixedwood site

In the boreal mixedwood region of Canada, management for conifer regeneration after clearcutting generally involvesmechanicalsitepreparation,plantingandaerialsprayingwithglyphosatetominimizepost-plantingcompetition from natural broadleaf regeneration. However, the resulting conifer plantations have economic and ecologicaldisadvantagescomparedwithmixedwoodstandswithhealthyandproductivebroadleafcomponents.This study examined 10-year growth of planted spruce and natural regeneration after pre- and post-harvest spraying andpartialcuttingtreatmentsonaborealmixedwoodsiteinnortheasternOntario,Canada.Thetreatmentswere as follows: (1) pre-harvest broadcast spraying with glyphosate to suppress trembling aspen (Populus tremuloides Michx.)regeneration,(2)clearcut (unsprayed)forbroadleafregeneration,(3)partialcuttosuppressshade-intolerant vegetation, and (4) post-harvest broadcast spraying to promote conventional conifer plantations. Planted spruce trees were tallest in the pre-harvest spray treatment but had the largest basal diameter in the postharvest spray treatment; neither of the differences was significant at 0.05. Total broadleaf regeneration density in the pre-harvest spray treatment was similar to that in the partial cut, but higher than that in the post-harvest spray treatment. Additional shade from greater amounts of shrubs and residual overstory trees in the partial cut treatment resulted in higher quality spruce trees than in the spray treatments; based on branch size, branch-free stem length and stem taper, wood quality was generally lowest in the post-harvest spray treatment. Pre-harvest spraying provided a better balance between growth and quality of planted spruce than either postharvest spraying or partial cutting.