Lessons learned from invasive plant control experiments: a systematic review and meta-analysis

Abstract

Summary1. Invasive plants can reduce biodiversity, alter ecosystem functions and have considerable economic impacts. Invasive plant control is therefore the focus of restoration research in invader-dominated ecosystems. Increasing the success of restoration practice requires analysis and synthesis of research findings and assessment of how experiments can be improved. 2. In a systematic review and meta-analysis of invasive plant control research papers, we asked: (i) what control efforts have been most successful; and (ii) what invasive plant control research best translates into successful restoration application? 3. The literature evaluated typically described experiments that were limited in scope. Most plot sizes were small ( <1 m 2 ), time frames were brief (51% evaluated control for one growing season or less) and few species and ecosystems (predominantly grasslands) were studied throughout much of the literature. The scale at which most experiments were conducted potentially limits relevance to the large scales at which restorations typically occur. 4. Most studies focused on invasive species removal and lacked an evaluation of native revegetation following removal. Few studies (33%) included active revegetation even though native species propagule limitation was common. Restoration success was frequently complicated by re-invasion or establishment of a novel invader. 5. Few studies (29%) evaluated the costs of invasive species control. Additionally, control sometimes had undesirable effects, including negative impacts to native species. 6. Synthesis and applications. Despite a sizeable literature on invasive plant control experiments, many large-scale invasive plant management efforts have had only moderate restoration success. We identified several limitations to successful invasive species control including: minimal focus on revegetation with natives after invasive removal, limited spatial and temporal scope of invasive plant control research, and incomplete evaluation of costs and benefits associated with invasive species management actions. We suggest that information needed to inform invasive plant management can be better provided if researchers specifically address these limitations. Many limitations can be addressed by involving managers in research, particularly through adaptive management.

Efficacy of Exotic Control Strategies for Restoring Coastal Prairie Grasses

“…Our results are consistent with many previous studies showing that both herbicides and mulch are effective in reducing exotic grass competition and favoring native grasses (e.g., Cox and Allen 2008;Huddleston and Young 2005;Irvine et al 2013;Kettenring and Adams 2011;Nyamai et al 2011). Exotic control treatments had much weaker and less consistent effects on cover of exotic forbs, which likely reflects the fact that cover of exotics forbs, many of which are low-stature and/or have basal rosettes, is strongly influenced by competition with taller-stature grasses, both native and exotic (Cox and Allen 2011;Hayes and Holl 2011).…”

“…While herbicides are commonly the most effective exotic control strategy and much cheaper than alternatives (Kephart 2001;Kettenring and Adams 2011), they are (Table 1) indicated a significant treatment effect (P , 0.05) but no treatment by mulch interaction, differences in whole-plot treatment means using Tukey's mean separation procedure are indicated with capital letters. When ANOVA (Table 1) showed a significant treatment by mulch interaction, differences across sub-plot treatment means are illustrated with lower case letters separately for unmulched (nonitalic) and mulched (italic) sub-plots.…”

“…Other studies have suggested that interannual climatic variation, which is beyond the control of practitioners, may be more important than the restoration method used (Cox and Allen 2011;Wilson et al 2004), so that investing resources in multiple years of seeding or planting may enhance restoration success more than expensive efforts to control exotic competition. What is clear is that long-term monitoring is needed to evaluate the efficacy of different restoration treatments, a call that has been made repeatedly in the academic literature (Matthews and Spyreas 2010;Rinella et al 2012), but is less commonly implemented (Kettenring and Adams 2011). Clearly, selecting among the options of no treatment, mulching, herbicide, and tarping will require balancing long-term efficacy with costs and logistical constraints at specific sites, as well as considering the effect of the treatments on any extant native vegetation and seed bank.…”

Management of invasive Phragmites australis in the Adirondacks: a cautionary tale about prospects of eradication

“…Where data exist, assessments are of limited duration (often only a single season) and plot sizes are small, typically \1 m 2 . This minimal focus on posttreatment monitoring and restoration is leading to widespread management failures (Kettenring and Adams 2011). We consider sustained and expanded collaborations between land managers and academic scientists a key mechanism for performing these outcome assessments and improving success of NIS management.…”

“…We consider pre-and post-treatment quantitative assessments an essential component of NIS management, especially given increasing evidence that treatments targeting NIS may have local unintended consequences on non-target (Keeley 2006;Kettenring and Adams 2011;Skurski et al 2013) and even listed species (Baker et al 2009). In some instances native species of conservation concern did better in the presence of non-indigenous plants when areas remained untreated compared to areas treated with herbicide (Pearson and Callaway 2008;Rinella et al 2009;Louhaichi et al 2012;Lazaran et al 2013).…”