This study was designed to test the hypothesis that herbicide (glyphosate, active ingredient) application for conifer release would reduce species diversity (measured as richness, Simpson's index, and Shannon-Wiener index) of both plant and small mammal communities over a 5-year period in young sub-boreal spruce (Picea engelmanniiParry ex Engelm. xPicea glauca(Moench) Voss) forest. Four treated and four untreated (control) sites were studied near Prince George in central British Columbia, Canada. Crown volume index of shrub vegetation was reduced by herbicide application. Species richness of shrubs was reduced in the first year after treatment and remained lower on treated sites throughout the 5-year period. Both indices of shrub diversity, however, were not different over the 5 years. Herbicide treatment initially reduced crown volume index of herbaceous vegetation, but values quickly recovered to untreated levels by the second year after treatment. Herbaceous species diversity was not affected by herbicide treatment. Diversity of small mammal communities apparently was not affected by herbicide application. In general, diversity of plant and small mammal communities seemed to be maintained, and hence, these treatment sites may not lower overall diversity of a forested landscape. Silvicultural practices, such as conifer release with herbicides or alternative methods, may contribute to a diversity of stand structures and wildlife habitats if appropriately designed and implemented.