Response of herbaceous plant community diversity and composition to overstorey harvest within riparian management zones in Northern Hardwoods

Partial timber harvest within riparian management zones (RMZs) may permit active management of riparian forests while protecting stream ecosystems, but impacts on herbaceous communities are poorly understood. We compared herbaceous plant community abundance, diversity and composition in RMZs along small streams in northern Minnesota, USA, among four treatments before harvest and 1 year and 9 years following treatment. Treatments included a no-harvesting control and three different treatments of the RMZs where the adjacent upland forest was clearcut: (1) an RMZ control, with no harvesting in the RMZ; (2) RMZ TL, in which the RMZ was partially harvested (60 per cent removal of basal area) using tree-length harvesting and (3) RMZ cut-to-length (CTL), in which the RMZ was partially cut (also 60 per cent removal) using CTL harvesting. Herbaceous cover, richness, diversity and most synecological coordinate scores (reflecting tolerances for light, heat, moisture and nutrients) varied over time but not among riparian treatments, whereas composition varied over time and by treatment but not differentially among treatments over time. These results indicate a lack of herbaceous plant community response to partial timber harvesting within these RMZs, which is consistent with previous work suggesting that understorey communities may be resistant to change below thresholds of disturbance intensity.