Overstory composition and stand structure influence herbaceous plant diversity in the mixed aspen forest of northern Minnesota

Abstract The relationship of herbaceous plant diversity to overstory composition and stand structure in the mixed aspen forest of northern Minnesota was investigated on 23 study sites that contained aspen in monoculture or in mixture with boreal conifers or northern hardwood species. On each site overstory species were placed into species groups: conifers, aspen and hardwoods other than aspen. Each site was then placed in one of three cover-type groups based on proportion of the overstory species groups: Aspen (>0.9 basal area in aspen), Aspen-Conifer (>0.15 basal area in conifer species) and Aspen-Hardwood (>0.15 basal area in hardwood species other than aspen). The relationships between diversity of herbaceous vegetation and the following factors were tested: (1) overstory composition, defined as the proportion of basal area by species group in the overstory and (2) stand structure. Stand structure was described by the vertical position and horizontal arrangement of balsam fir within the stand. In addit...