Species composition in two boreal mixedwoods before and 10 years after hexazinone treatment for establishing underplanted Picea glauca (Moench) Voss

Abstract The vegetational species composition was determined in eight 10 m × 10 m plots at the beginning of a study in 1978 in two shrubby mixedwood stands near Chapleau in boreal Ontario. At the center of each plot, 16 Picea glauca (Moench) Voss 2 + 2 transplants were underplanted in a 4 × 4 grid at either close (95 cm × 95 cm) or wide (163 cm × 163 cm) spacing. At each location, there were two replications of each of four treatments: close-planted spruce without other treatment (control), closeplanted spruce and Gridball TM pellets applied at 95 cm × 95 cm grid spacing (4.2 kg a.i. ha −1 hexazinone), wide-planted spruce without other treatment, and wide-planted spruce and Gridballs TM at 163 cm × 163 cm spacing (1.4 kg a.i. ha −1 hexazinone). The herbicide pellets were placed by hand on the ground throughout the treated plots, one at each point of intersection of the appropriate grid lines to maximize separation between the herbicide and the outplants. Species composition was determined again ten growing seasons later. On the less fertile site, there was no evidence that species composition had been influenced by hexazinone treatment. On the more fertile site, though the indices of similarity were lowest for the comparisons between the control and the hexazinone treatments, only one initially present species was absent from the herbicide-treated plots in 1988. Ten years after application, Gridballs TM had no detectable effect on species composition.