This study was designed to evaluate changes in plant biomass, species richness, and diversity after application of glyphosate herbicide in several successional stages of sub-boreal spruce forest near Prince George, British Columbia, Canada. Vegetation was sampled in replicate control (reference) and treatment blocks of “herb,” “shrub,” and “shrub-tree” stages of cutover forest habitats. Volume of herb layers declined temporarily in the first post-treatment year. Shrub layers were reduced in herb and shrub stages, and shrubs and trees were reduced temporarily in the shrub-tree stage. Species richness of herbs and shrubs was similar in control and treatment blocks in the herb successional stage, but shrub richness declined on the treatment in the shrub stage. There were no consistent differences in numbers of herb, shrub, or tree species between control and treatment blocks in the shrub-tree stage. Species diversity (Simpson's index and Shannon-Wiener function) of herbaceous plants was not affected by herbicide application in any of the successional stages, but diversity of shrubs was lower in treatment than control blocks in the herb and shrub stages. Diversity of trees was reduced on treatment blocks in the shrub-tree stage. Species abundance curves of overall plant communities showed little change in the herb stage, a decline in the first post-treatment year in the shrub and shrub-tree stages, with similar patterns between control and treatment blocks in subsequent post-treatment years. The general lack of community-wide reductions in plant biomass and diversity, and the short-term duration of specific changes, suggest that conifer release treatments of plantations have no substantial, incremental effects on wildlife habitat.

Weed control and red pine release by spotgun-applied hexazinone in a northern Ontario plantation were evaluated 3 yr after treatment, while hexazinone residues and lateral movement in the sandy loam soil were determined 1 yr after treatment. Hexazinone, grid pattern spot applied at 480 mg ai/spot, approximating 1.6 kg ai/ha, resulted in 88% quaking aspen stem dieback and variable suppression of white birch and pin cherry. The height and basal diam of treated red pine were 131 and 150% of control, respectively, after 3 yr. Hexazinone residues were reduced to 1% at the treated spot and did not move laterally beyond 0.5 m, 1 yr after treatment. Detection of small amounts of metabolites A and B (0.2 and 0.3%) indicated the non-cumulative degradation of hexazinone in soils.