Short-term changes in vegetation after the silvicultural spraying of glyphosate herbicide onto regenerating clearcuts in Nova Scotia, Canada

Abstract

Glyphosate herbicide was applied by helicopter to release small conifer plants from the effects of competition with silvicultural "weeds" on regenerating clearcuts at four study sites. Prior to clear-cutting the study sites were (i) a mixed conifer-hardwood stand in which the regeneration was dominated by red maple (Acerrubrum L.), raspberries, and dicotyledonous herbs; (ii) a conifer stand, with regeneration dominated by heath shrubs, bracken, and birches; (iii) an old-field stand of white spruce (Piceaglauca (Moench) Voss), with regeneration dominated by alder, Asteraceae, and graminoids; and (iv) a mixed conifer–hardwood stand, with regeneration dominated by red maple, raspberries, Asteraceae, and graminoids. The study design included spray and reference (unsprayed) plots at each study site, and prespray surveys of vegetation in permanent plots, followed by as many as 6 years of measurement of regeneration after herbicide treatment. Aerial glyphosate treatment caused large decreases in the abundance of vegetation, especially of pteridophytes and herbaceous and woody angiosperms. There was a substantial recovery of some plant taxa by the end of the first and second postspray growing seasons, especially raspberry and various herbaceous angiosperms. By the end of the study period, no plant taxa had been eliminated, but there were substantial changes in relative abundance. In particular, conifers had a relatively greater abundance on sprayed plots than on unsprayed plots, suggesting that sprayed clearcuts will more rapidly develop into conifer-dominated stands.