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.

Effects of herbicide treatments on biotic components in regenerating northern forests

“…Stand-level biomass reductions of non-conifer vegetation (commonly 50-70% during the first year after treatment, but varying by vegetative group - Fig. 1) have consistently followed site-preparation and conifer release treatments in a variety of northern ecosystems (Newton et al 1992;Pitt et al 1992Pitt et al , 1993Pitt et al , 2000Freedman et al 1993;Raymond et al 1996;Bell et al 1997;Kelly et al 1998;Sullivan et al 1998a;Vreeland et al 1998;Gagné et al 1999;Lindgren and Sullivan 2001). However, operationally effective conifer release treatments generally eliminate few, if any, of the species from treated sites (Morrison and Meslow 1983;Newton et al 1989;Santillo et al 1989;Lautenschlager ,1993aHorsley 1994;Bell and Newmaster 1998 by the end of 2 years.…”

“…Volume growth of conifer seedlings consistently increases after competition is controlled (Walstad and Kuch 1987, Newton et al 1992, Freedman et al 1993, Wagner et al 1999). This and other management realities have led to the suggestion that repeated herbicide treatments, or other silvicultural practices (e.g., genetic improvement, fertilization), could produce an eight-fold increase in conifer production on selected sites in Canadian forests (Taylor 1999, Lautenschlager 2000.…”

“…Lindgren and Sullivan 2001). Indeed, plant species richness and related diversity indices often remain the same or increase on treated sites, because resident species generally remain and new species invade to occupy newly created niches (Swindel et al 1984, Lautenschlager and McCormack 1989, Jobidon 1990, Freedman et al 1993, Horsley 1994, Simard and Heinemann 1996, Sullivan et al 1998a, Boateng et al 2000, Lindgren and Sullivan 2001. Species are not eliminated because "(1) treatments are not designed to remove all competing vegetation but rather to reduce the level of competition; (2) treated areas often contain 'skips' (unintentionally unsprayed areas); (3) minimum effective volumes For personal use only.…”

The Risks Associated with Glyphosate-Based Herbicide Use in Planted Forests

“…Indirect effects of glyphosate to both terrestrial and aquatic fauna have been associated with changes in plant community composition, habitat structure, cover, and food sources and are primarily a consequence of glyphosate's phytotoxic effects rather than a result of ecotoxic qualities unique to the active ingredient [80,99,[107][108][109][110]. Studies on small mammals (i.e., rodents, shrews, voles, chipmunks) showed that some short-term changes were observed at the species [111][112][113] and functional feeding group level [114], which the authors attributed to the reduction in invertebrates, plant cover and food.…”

Negative or positive effects of plantation and intensive forestry on biodiversity: A matter of scale and perspective

“…The greatest impact of these treatments is on the availability of dead organic matter-cavity trees, snags, coarse woody debris, and the organic horizon of the forest floor (Freedman et al 1993(Freedman et al , 1996-and minimizing intensive site preparation will help maintain coarse woody debris and thus biodiversity (Carey and Johnson 1995). Plant species diversity is not at all or somewhat positively affected by ploughing or tilling (Haeussler et al 2002(Haeussler et al , 2004, but moderate treatments may be necessary to prevent site colonization by ruderal plants (Soo et al 2009) and other early colonizers, many of which could be invaders.…”