Effets comparatifs de la préparation mécanique du sol et de l'application répétée d'un phytocide chimique pour maîtriser le nerprun et favoriser la croissance en plantations forestières

Abstract

Glossy buckthorn (Frangula alnus) is an exotic, invasive species that reduces white spruce (Picea glauca) plantationgrowth in Québec. Chemical herbicide applications, usually repeated more than once, are the only vegetation management approach known to control the species effectively. Its use, however, raises social and environmental issues. Our objective was thus to evaluate mechanical site preparation as a vegetation management tool to control glossy buckthorn on reforestation sites. We compared, after four years, three mechanical site preparation treatments (including windrowing as a control) and a scenario of repeated chemical herbicide applications in a fully randomized complete block design. Globally, mechanical site preparation by harrowing or mixing did not have significant short-term effect on buckthorn control and planted spruce dimensions, compared to windrowing. Windrowing followed by repeated chemical herbicide applications had a significant but limited effect on buckthorn modal height. Whereas the chemical treatment did not promote height growth of planted seedlings, it significantly increased diameter. Hence, mechanical site preparation using harrowing or mixing does not seem to be an effective alternative to repeated chemical herbicide applications following windrowing to control glossy buckthorn. Site invasion by this species thus raises a major issue regarding planted ecosystems productivity, especially in contexts where chemical herbicides cannot be used. Global changes might exacerbate this issue as well as the invasion of natural forests by extending the geographic distribution of the species.