Removing Chinese Privet from Riparian Forests Still Benefits

Biological Conservation 167 (2013) 355–362 Contents lists available at ScienceDirect Biological Conservation journal homepage: www.elsevier.com/locate/biocon Removing Chinese privet from riparian forests still benefits pollinators five years later ⇑ Jacob R. Hudson a, , James L. Hanula b, Scott Horn b a University of Georgia, Department of Entomology, Athens, GA 30602, USA b U.S. Forest Service, Southern Research Station, Athens, GA 30602, USA article info abstract Article history: Chinese privet (Ligustrum sinense) is an invasive shrub of the Southeastern U.S. that forms dense stands Received 10 June 2013 and limits biodiversity. It was removed from heavily infested riparian forests of the Georgia Piedmont in Received in revised form 27 August 2013 2005 by mulching machine or chainsaw felling and subsequent herbicide application. Abundance and Accepted 1 September 2013 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 Keywords: in numbers of species. Traps on removal plots captured four times more individuals than those on control Invasive plants plots and similar numbers to reference plots. Bee and butterfly abundance and richness were positively Chinese privet Long term correlated with non-privet plant cover, diversity, and evenness and negatively correlated with privet Pollinators shrub cover. Removing Chinese privet from riparian forests had a beneficial effect on insect pollinator Bees communities five years after removal and is a relatively simple method of improving pollinator habitat. Butterflies 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. Published by Elsevier Ltd. 1. Introduction (NAS, 2007). Pollinators also provide an estimated 2–3 billion dol- lars in pollination services each year to agricultural systems and Invasive plants are a severe threat to the biodiversity of forests high levels of infestation by invasive plants in forested areas near worldwide. While directly competing with native plants for light, agricultural fields have the potential to decrease floral visitation water, and nutrients (Morris et al., 2002), invaders also compete rates to nearby crops (Ricketts, 2004; Losey and Vaughan, 2006; with native plants for floral visits from pollinators which can fur- Garibaldi et al., 2013). ther limit propagation and biodiversity (McKinney and Goodell, Previous studies examined invasive plant and native bee inter- 2010). Chinese privet, Ligustrum sinense Lour. (Oleaceae), is an actions and have reported conflicting results. Invasive plants like invasive shrub widely distributed in the Southeastern U.S. In Chinese privet may attract more generalist bees with copious 2008, it was estimated to inhabit over 1 million ha of forest land amounts of pollen and increase their abundance during their short with an unknown amount of infested land around cities, towns, flowering period, yet may reduce the presence of specialist bees and roadside or field edges (Miller et al., 2008). and the rare or threatened plant species that they visit (Tepedino Invasive shrubs like Chinese privet have the potential to affect et al., 2008; Baskett et al., 2011). Williams et al. (2011) suggest that invertebrate communities by reducing plant abundance, diversity, although bees use invasive plants in highly disturbed areas, they and host plants of specialized herbivores (Crisp et al., 1998; Sie- rarely prefer them. Still numerous other studies show that non-na- mann, 1998; Haddad et al., 2001, 2009; Biesmeijer et al., 2006). tive invasive plants can reduce bee pollination of native plants Bees (Hymenoptera: Apoidea) may be especially affected by the (Grabas and Laverty, 1999; Brown et al., 2002; Ghazoul, 2004; Tra- extensive shade privet produces and resulting reduction in herba- veset and Richardson, 2006; Aizen et al., 2008; Vanparys et al., ceous plant cover beneath it (Ghazoul, 2004; Hanula and Horn, 2008; Muñoz and Cavieres, 2008; McKinney and Goodell, 2010; 2011b; Ebeling et al., 2012). These insects help maintain plant King and Sargent, 2012; Gibson et al. 2013). communities in natural areas, which in turn impacts many ecosys- Butterflies (Lepidoptera: Rhopalocera) may also be negatively tem functions including water filtration and carbon sequestration affected by Chinese privet. Butterflies are one of the most recogniz- able insect groups to the public and they have been proposed as an ⇑ Corresponding author. Address: 972 Philadelphia Rd., Deville, LA 71328, USA. umbrella taxon to detect changes in other natural communities Tel.: +1 318 446 4223. (New, 1997). Although pesticide use and loss of habitat are factors E-mail address: [email protected] (J.R. Hudson). 0006-3207/$ - see front matter Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.biocon.2013.09.001 356 J.R. Hudson et al. / Biological Conservation 167 (2013) 355–362 that can contribute to reduced butterfly abundance and diversity, the plot. At the same time in nearby plots, crews with chainsaws Wagner and Van Driesche (2010) regard invasive plants as the and machetes cut privet and left the debris where it fell. The plots greatest threat to them in eastern North America. Unlike bees, but- created in this way are referred to as ‘‘hand-felling’’. The stumps in terfly larvae feed directly on specific host plants or groups and exo- both treatment plots were sprayed with either 30% triclopyr (Gar- tic plants only support a fraction of the species that native plants lon 4Ò) or 30% glyphosate (ForestersÒ) herbicide to prevent re- do (Tallamy and Shropshire, 2009). sprouting. The herbicide used at each location was selected by Past studies have explored the role of native pollinators in the the location’s manager. One year later, in December 2006, sprouts propagation of invasive plants (Bartomeus et al., 2008; Tepedino and seedlings were sprayed with 2% glyphosate using back pack et al., 2008; Williams et al., 2011). While these interactions may sprayers or mist blowers. By the next summer (2007), less than be important to understand the mechanism of invasion, few stud- 1% of privet remained in the shrub and herbaceous layers in both ies have looked at degradation of an area due to invasion and its treatment plots (Hanula et al., 2009). effect on native pollinators. Valtonen et al. (2006) found a de- Plant communities five years after removal were reported in creased abundance and diversity of Lepidoptera in road verges Hudson (2013). Chinese privet re-infested approximately 7% of inhabited by an invasive plant while shade produced by invasive mulched plots and 3% of hand-felling plots. Non-privet herbaceous shrubs has been shown to reduce presence of bees (McKinney plants covered 70% of mulched plots and 60% of hand-felling plots and Goodell, 2010; Hanula and Horn, 2011b; Fiedler et al., 2012) which was higher than the 20% in control plots. Herbaceous plant and butterflies (Hanula and Horn, 2011a; Fiedler et al., 2012). cover on removal plots was similar to desired plots (70%). Species Therefore, removing an invasive plant species may act to increase richness of herbaceous plants was also higher in removal and de- abundance and richness of native pollinator communities in the sired plots than control plots. short term but little is known about long term effects. Still initial studies have produced encouraging results. Removing Chinese pri- 2.3. Pollinator sampling vet from riparian forests increased richness and abundance of both bees and butterflies for two years following treatment (Hanula and Bees and butterflies were sampled for one week out of each Horn, 2011a,b). Removing Frangula alnus from prairie fens (Fiedler month from March to October 2012 on mulched, hand-felling, con- et al., 2012) or invasive plants from forests on a tropical island (Flo- trol, and desired future condition plots. Blue and yellow pan traps rens et al., 2010) had the same short term effect. (SoloÒ plastic bowls) were used to capture both groups (Campbell We examined the effects of two methods for eliminating Chi- and Hanula, 2007). Pan traps were filled with soapy water and sus- nese privet from riparian forests on bee and butterfly communities pended above the ground ca. 30 cm using heavy gauge metal wire. five years after removal. The communities on plots where privet Ten pan traps (five of each color) were placed in each 2 ha plot at was removed were compared to those on heavily invaded control five, 0.04 ha sub-plots (one blue and one yellow at each subplot). plots and to plots with historically little or no privet invasion. The subplots were located at the center and half the distance from We also examined how the communities changed from 2007 to the center to each corner. 2012. Differences in the vegetation structure of removal and control plots were not expected to impact the effectiveness of pan traps. Traps were most visible below the privet canopy in control plots 2. Material and methods and were often the only source of ‘‘floral’’ color there. Plant cover in removal plots included tall (up to 2 m) herbaceous species as 2.1. Study areas well as similar sized or taller tree saplings that reduced visibility of the bowls. Despite this, pan traps were effective for pollinators. The study sites are described in detail by Hanula et al. (2009). After each sampling period, insects were collected and stored in Briefly, four study areas were chosen within the Oconee River wa- 70% ethyl alcohol until they could be sorted, pinned, and identified. tershed in Northeast Georgia that were heavily infested with Chi- Bees were identified using published keys (Mitchell, 1960; Gibbs, nese privet. Two of these areas, the Botanical Gardens of Georgia 2010) and a reference collection, and butterflies were identified and Sandy Creek Nature Center, are located around Athens, Georgia using field guides (Opler and Malikul, 1992; Daniels, 2004).

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