Are lepidopteran communities resilient to timber harvest?

Background/Question/Methods A common measure of ecosystem resilience is the timecourse to recovery for a system that has been previously disturbed. While resilience has been explored in aquatic and grassland systems, resilience of forest systems to harvest disturbances is poorly understood. The goal of this study was to assess whether forest lepidopteran communities displayed three different forms of resilience following experimental timber harvest. Specifically, I examined whether moth species assemblages returned to pre-logging composition (compositional resilience), species richness (structural resilience), and guild diversity (functional resilience) after forest management. Lepidoptera were sampled from 16 forest stands managed with one of four harvest treatments: no logging, clearcutting, shelterwood harvests, and group-selection harvests. Moths were sampled from all forest stands one year prior to harvest in 2007 and immediately post-harvest in 2009-2012.

Results/Conclusions Moth community composition only appeared to be resilient to timber harvest in stands managed with shelterwood methods or in the unlogged stands within managed concession units. Both total species richness and species richness of Quercus-feeding moths also appeared to recover to a near original condition three years post-shelterwood logging. In contrast, moth assemblages in clear cut stands and group-selection stands remained impoverished. Tests of functional resilience suggested that richness of species known to be pollinators was largely unaffected by timber management, and moth assemblages in stands logged using group selection methods actually gained species in the herbaceous feeding guild. Dietary specialists were disproportionately abundant in the unlogged stands post-harvest, suggesting that species with more narrow dietary niches have the lowest resilience to timber management. These results suggest that most methods of forest management have short-term negative impacts on woody-plant feeding Lepidoptera, but that the effects are limited to a few years when the harvest method involves shelterwood cuts. Herbaceous-feeding Lepidoptera appear to quickly colonize stands managed with group-selection or clear cutting, so loss of species richness in stands managed with either of these treatments may be less than predicted based on level of timber being removed. Recovery of moth assemblages in more highly disturbed stands will require longer time periods and techniques such as group-selection harvests, where upwards of 80% of the standing bole is removed, may not be consistent with conservation goals.