Abstract

Fast-growing trees such as hybrid poplars ( Populus) have the potential to decrease rotation length (time to harvest) and thus produce wood products more quickly from smaller areas of land. Several forest companies in Quebec currently plant hybrid poplar on formerly logged forest sites, rather than on agricultural land as is more common elsewhere. The forest sites often have acidic soils, and lime addition has been proposed to improve hybrid poplar growth. In addition, forest sites present challenges with regard to control of competitive vegetation, particularly in jurisdictions such as Quebec where use of herbicides in forests is banned or restricted. Our study investigated the impacts of lime treatments (0, 2000 or 4000 kg ha −1) on non-crop vegetation on forest sites planted to hybrid poplar. Soil and plant data were obtained from 270 experimental plots in southern Quebec, divided between two study sites. Soil pH before treatment ranged from 3.9 to 5.7, with means of 4.7 and 5.0, respectively, at the two sites. Weed data were obtained 2 years after treatment from 20 microsites per plot (5400 in total). Parameters included total cover by all weeds combined and cover by particular subcategories. Hybrid poplar growth and nutrition were also measured. Lime increased soil pH, soil exchangeable calcium and hybrid poplar growth. Total weed cover did not differ significantly by lime treatment, nor did cover by major subgroups such as grasses and grasslike plants, forbs or woody species. Soil pH (both pre- and post-treatment) was positively correlated with post-treatment weed height, grass cover, forb cover and hybrid poplar growth. It was negatively correlated with cover by woody non-crop plants. The relationships between pH and particular weed groups suggest that more intensive liming, and/or greater time since lime application, could favour certain vegetation types over others (e.g., grasses and grasslike species over woody non-crop plants), although no large-scale shifts were detectable within the scope of our study.

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