Removing Chinese privet from riparian forests still benefits pollinators five years later

Keywords: Invasive plants Chinese privet Long term Pollinators Bees Butterflies a b s t r a c t Chinese privet (Ligustrum sinense) is an invasive shrub of the Southeastern U.S. that forms dense stands and limits biodiversity. It was removed from heavily infested riparian forests of the Georgia Piedmont in 2005 by mulching machine or chainsaw felling and subsequent herbicide application. Abundance and species richness of bees and butterflies were sampled using pan traps on removal plots, heavily invaded control plots, and reference plots in 2012, approximately five years after complete removal of privet. Removal plots had nearly three times as many species as control plots and were similar to reference plots in numbers of species. Traps on removal plots captured four times more individuals than those on control plots and similar numbers to reference plots. Bee and butterfly abundance and richness were positively correlated with non-privet plant cover, diversity, and evenness and negatively correlated with privet shrub cover. Removing Chinese privet from riparian forests had a beneficial effect on insect pollinator communities five years after removal and is a relatively simple method of improving pollinator habitat. These findings provide justification for allocating resources for invasive shrub species removal to support long term conservation of these important insect groups and the ecological services they provide. Invasive plants are a severe threat to the biodiversity of forests worldwide. While directly competing with native plants for light, water, and nutrients (Morris et al., 2002), invaders also compete with native plants for floral visits from pollinators which can further limit propagation and biodiversity (McKinney and Goodell, 2010). Chinese privet, Ligustrum sinense Lour. (Oleaceae), is an invasive shrub widely distributed in the Southeastern U.S. In 2008, it was estimated to inhabit over 1 million ha of forest land with an unknown amount of infested land around cities, towns, and roadside or field edges (Miller et al., 2008). Invasive shrubs like Chinese privet have the potential to affect invertebrate communities by reducing plant abundance, diversity, and host plants of specialized herbivores (Crisp et al. Bees (Hymenoptera: Apoidea) may be especially affected by the extensive shade privet produces and resulting reduction in herba-ceous plant cover beneath it (Ghazoul, 2004; Hanula and Horn, 2011b; Ebeling et al., 2012). These insects help maintain plant communities in natural areas, which in turn impacts many ecosystem functions including water filtration and carbon sequestration (NAS, 2007). Pollinators also provide an estimated …