Short-Term Response of Native Flora to the Removal of Non-Native Shrubs in Mixed-Hardwood Forests of Indiana, USA

Joshua Shields,John Dunning,Patrick Zollner,Michael Saunders,Michael Jenkins,Kevin Gibson

doi:10.3390/f6061878

Abstract

While negative impacts of invasive species on native communities are well documented, less is known about how these communities respond to the removal of established populations of invasive species. With regard to invasive shrubs, studies examining native community response to removal at scales greater than experimental plots are lacking. We examined short-term effects of removing Lonicera maackii (Amur honeysuckle) and other non-native shrubs on native plant taxa in six mixed-hardwood forests. Each study site contained two 0.64 ha sample areas—an area where all non-native shrubs were removed and a reference area where no treatment was implemented. We sampled vegetation in the spring and summer before and after non-native shrubs were removed. Cover and diversity of native species, and densities of native woody seedlings, increased after shrub removal. However, we also observed significant increases in L. maackii seedling densities and Alliaria petiolata (garlic mustard) cover in removal areas. Changes in reference areas were less pronounced and mostly non-significant. Our results suggest that removing non-native shrubs allows short-term recovery of native communities across a range of invasion intensities. However, successful restoration will likely depend on renewed competition with invasive species that re-colonize treatment areas, the influence of herbivores, and subsequent control efforts.

Highlights

As land managers with limited resources strive to counteract the negative effects of invasive species, context-dependent information about the invader and the invaded ecosystem becomes increasing critical.an understanding of effective control strategies, spatial and temporal processes, and biotic and abiotic factors contributing to successful invasion are all important when prioritizing management actions
In 2010, mean L. maackii density was 2372 ± 480 shrubs·ha−1 in the sapling stratum in removal areas; we found no L. maackii shrubs ≥1.37 m tall in removal areas in 2011 (Figure 2)
Mean L. maackii seedling density increased from 5382 ± 1389 shrubs/ha to only 6424 ± 1480 shrubs/ha (p = 0.17)

Summary

Introduction

As land managers with limited resources strive to counteract the negative effects of invasive species, context-dependent information about the invader and the invaded ecosystem becomes increasing critical.an understanding of effective control strategies, spatial and temporal processes, and biotic and abiotic factors contributing to successful invasion are all important when prioritizing management actions. As land managers with limited resources strive to counteract the negative effects of invasive species, context-dependent information about the invader and the invaded ecosystem becomes increasing critical. In the case of invasive plants, restoration efforts often focus upon the removal of invasives with the goal of allowing native species to re-establish. Within forest ecosystems, woody invasive shrubs are problematic because their longevity and persistence in the understory exerts considerable influence over herbaceous-layer processes, including forest regeneration [3]. These species are often able to establish in forest understories in the absence of overstory disturbance [4]. Lonicera maackii (Amur honeysuckle), an invasive shrub introduced from Asia [5], has become a serious management concern in forests across much of eastern

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