Variable effects of timber harvest on the survival, growth, and reproduction of American ginseng (Panax quinquefolius L.)

Timber harvest is a recurrent, widespread canopy disturbance that has long-affected the eastern decid- uous forest. Multi-dimensional shifts in forest dynamics occur following timbering, and while a great deal of research on tree response to timbering has been performed, far less focus has been placed on herba- ceous understory response to timbering. American ginseng (Panax quinquefolius L.) is a long-lived, eco- nomically valuable medicinal herb believed to be adapted to the dynamic light conditions of old- growth forests. The purpose of this study was to determine if timber harvests of varying intensity had positive, neutral, or negative effects on the survival, growth, and reproduction of wild American ginseng. Hemispherical images were used to calculate the canopy openness above ginseng plants. Population cen- sus data were used to obtain measurements of survival, relative growth rate, seed production, seed pro- duction efficiency, and new seedling emergence. Changes in survival and seed production in response to timbering were analyzed using log-likelihood analyses, and the responses of relative growth rate and seed production efficiency to timbering were analyzed using nested two-way ANOVAs. Initial ginseng survival varied among sites, with lowest survival at the more intensely timbered site. Additionally, long-term survival decreased following timbering. Relative growth rate of individuals increased following timbering in both short-term and long-term analyses, with relative growth rate being greatest at sites where more tree biomass was removed. While seed production decreased the year directly following tim- bering, seed production increased over the three years after timbering. Both short-term and long-term effects of timbering on seed production efficiency differed among populations. While seed production increases in the years after timbering, this stimulation may not be realized due to sub-optimal germina- tion conditions. Due both to decreases in survival following timbering and the unlikely continued increases in growth and seed production as the canopy fills in, some of these often-used timbering strate- gies negatively impact ginseng performance. Silvicultural strategies that mimic old-growth forest struc- ture may be better suited for the conservation of ginseng and other similar obligate understory species. 2015 Elsevier B.V. All rights reserved.