Response of seven hardwood tree species to herbicide, rototilling, and legume cover at two southern Quebec plantation sites

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Abstract
Two experimental plantations of valuable hardwoods were established in southern Quebec, at the northern limit of the North American deciduous forest, to examine the effects of three weed control treatments on the growth of tree seedlings. Treatments of herbicide, rototilling, and sowing of a legume cover (Lotus corniculatus L. and Trifolium repens L.) were applied to seven tree species (Fraxinus americana L., Juglans nigra L., Prunus serotina Ehrh., Quercus alba L., Quercus macrocarpa Michx., Quercus rubra L., Tilia americana L.). A control treatment, retaining existing herbaceous vegetation, was also included. After three growing seasons tree growth was highest in the herbicide and rototilling treatments. Improved growth was associated with high foliar nitrogen, and sometimes phosphorus, content. The growth gains provided by weed control were reduced on the site with the poorest soil drainage. Despite the introduction of herbaceous legumes, the weed biomass increased during the first 2 years, and tree growth in this treatment was rarely superior to the control. The growth obtained for some species in the best treatment, generally the herbicide, was similar to that attained farther south in Ontario.