Does Removal of Invasive Garlic Mustard Affect Eastern Red-backed Salamanders?

One challenge facing land managers is the invasion of non-native plants (Westman 1990, D'Antonio and Meyerson 2002). Decisions on remediation and removal of non-native plants need to be placed into a cost-benefit context, taking into account the costs and impacts of removal since not all invasive plants have the same impact (e.g., Hiebert 1997). Removal of many invasive plants is very expensive and time-consuming (Blossey et al. 2001, Marais et al. 2004), but can have positive outcomes on native species and ecosystems (e.g., Holsman et al. 2010). However, removal of invasive species can have unintended, or even problematic, outcomes (Rinella et al. 2009, Zipkin et al. 2009). Therefore, we need a better understanding of the potential benefits of invasive plant removal on the native flora and fauna.

One very successful invader of the forests and woods of the northeastern and midwestern United States is Alliaria petiolata (garlic mustard). Alliaria petiolata has spread throughout the northeast and into Canada and the midwestern U.S. from its introduction on Long Island, New York in 1868 (Welk et al. 2002). Little is known about the impacts of A. petiolata invasions on the fauna of invaded communities. However, given the ability of garlic mustard to replace the native understory plant communities (Anderson et al. 1996, McCarthy 1997, Van Riper et al. 2010; but see Davis et al. 2015), it seems likely that any invasion by A. petiolata has the potential to impact the local fauna, either directly through alterations of the physical environment or indirectly through alterations of the prey community, especially given the high densities these populations can reach in invaded areas (density on the study area = 136 m–2; Smith et al. 2003; density ranges up to almost 300 m–2 in other populations; Anderson et al. 1996, Byers and Quinn 1998). Here, I report the results of an experiment designed to assess the effects of garlic mustard removal on Plethodon cinereus (Eastern Red-backed Salamander). Plethodontid salamanders, especially P. cinereus, are important components of the fauna of temperate forests in eastern North America (Davic and Welsh 2004).

Figure 1.

Mean (± SE) number of surface active Plethodon cinereus (Eastern Red-backed Salamanders) found under cover boards in Alliaria petiolata (garlic mustard) removal plots (open circles) and control plots (closed circles) across the study period.

In the summer of 2001, I established removal and control plots in an upland beech-maple-oak woodland in the Denison University Biological Reserve located in Granville, Licking Co., Ohio (see Smith et al. 2003 for additional details). Each plot was 10 m × 10 m. Plots were laid out in three sites. Each site consisted of two replicates of the A. petiolata removal treatment and two replicates of the control treatment (total number of replicates = 6 for each treatment). Plots within a site were separated by a 5-m buffer strip that was unmanipulated, and sites were separated by at least 50 m.

All A. petiolata were removed by hand from the removal plots, and the control plots were not manipulated. Removals took place in early June 2001, and then again in early June 2002. Following the 2002 removal, I monitored salamander abundance using coverboard arrays (61-cm × 30.5-cm, 4-cm thick untreated lumber; five per plot). I counted the salamanders under cover boards every 2 weeks from August 14 to November 20, 2002; April 1 to October 1, 2003; and April 14 2004.

Because P. cinereus in this area has two surface activity peaks, one in the spring and one in the fall, and virtually no surface activity in the summer (Grasser and Smith 2014), I only included spring (April and May) and fall (September to November) counts in the analysis. I used a repeated measures ANOVA to compare the total number of salamanders found under cover boards on each visit for each replicate from the removal and control treatments. Statistical analyses were performed using JMP Pro 13 (SAS Institute, Cary, NC).

There was no significant effect of A. petiolata removal on the...