SHORT-TERM CHANGES IN VEGETATION AFTER THE SILVICUTURAL SPRAYING OF GLYPHOSATE HERBICIDE ONTO REGENERATING CLEARCUTS IN NOVA-SCOTIA, CANADA

Glyphosate herbicide was applied by helicopter to release small conife r 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 r egeneration was dominated by red maple (Acer rubrum L.), raspberries, and dicotyledonous herbs; (ii) a conifer stand, with regeneration domi nated by heath shrubs, bracken, and birches; (iii) an old-field stand of white spruce (Picea glauca (Moench) Voss), with regeneration domina ted by alder, Asteraceae, and graminoids; and (iv) a mixed conifer-har dwood stand, with regeneration dominated by red maple, raspberries, As teraceae, and graminoids. The study design included spray and referenc e (unsprayed) plots at each study site, and prespray surveys of vegeta tion in permanent plots, followed by as many as 6 years of measurement of regeneration after herbicide treatment. Aerial glyphosate treatmen t caused large decreases in the abundance of vegetation, especially of pteridophytes and herbaceous and woody angiosperms. There was a subst antial 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 e liminated, but there were substantial changes in relative abundance. I n particular, conifers had a relatively greater abundance on sprayed p lots than on unsprayed plots, suggesting that sprayed clearcuts will m ore rapidly develop into conifer-dominated stands.