Life After Privet: Plant Community Dynamics in a Forested Wetland Following Removal of the Invasive Ligustrum sinense Lour

Abstract

Chinese privet (Ligustrum sinense) invasion has been found to reduce native species richness and abundance of both herbaceous and woody plants and is a serious threat to wetlands in the southeastern United States. To determine the relationship between privet removal and understory vegetation, we performed surveys on a forested wetland from which L. sinense had been partially removed over a two-year period. Plant community composition, vegetation cover and species richness as well as soil moisture and PAR were recorded in removal and control (Privet-Present) plots in herb, shrub and tree layers. As expected, herb-layer removal plots were wetter and less shady, with more than four times higher cover of native and non-native species. Total species richness and native species richness were both higher in herb-layer removal plots, though non-native species richness did not differ. Shrub-layer removal plots were much less dense, with 1/100 the basal area of shrubs than control plots. Tree-layer plots did not differ in any measure, suggesting that control and removal plot types were historically similar and continued to support comparable overstory vegetation. The composition of woody seedlings in the herb layer did not reflect the mature overstory in either plot type, although several of the most abundant woody seedlings were those of dominant wetland species. We conclude that immediately following L. sinense removal, native species outperform non-natives, both in cover and species richness in the herb layer. The poor recruitment of woody seedlings and saplings as well as the rapid invasion of invasive Japanese stiltgrass (Microstegium vimineum) may thwart restoration efforts, however. To ensure the wetland reaches its pre-invasion community structure, it may be necessary to plant native tree saplings and nurture them through the shrub layer to maturity.