Native plant community response to alien plant invasion and removal

effective elimination of alien plants and the restoration of the native plant species community back to its historical composition and function (Zavaleta et al. 2001; SER 2002; Hulme 2006). In order to effectively control invasions, an assessment of the magnitude of their impacts is also required (Stinson et al. 2007). T h u s , a c o m p r e h e n s i v e understanding of the success of alien plant management, would ideally involve observational and experimental comparative studies between invaded, non-invaded and removal sites, that asses the impacts of the alien plant and the resulting native species assemblage, after its removal.

been successful requires both, the effective elimination of alien plants and the restoration of the native plant species community back to its historical composition and function (Zavaleta et al. 2001;SER 2002;Hulme 2006).In order to effectively control invasions, an assessment of the magnitude of their impacts is also required (Stinson et al. 2007).impacts have also been reported (Pimentel et al. 2005;Kettunen et al. 2009;Vilà et al. 2010).Given these ecological and socioeconomic impacts, management of alien plants has become an important challenge and a high priority for the conservation of native species and natural areas (Zavaleta et al. 2001;Smith et al. 2006;Swab et al. 2008).
In many natural areas Our results that invasion by alien plants is responsible for a local decline in native species richness and abundance.
Our analysis also provides evidence that after removal, the native vegetation has the potential to recover to a pre-

Non-invaded reference sites
Removal sites Figure 1: Schematic diagram that summarize the different types of comparison that can be used to assess the impact of an invader and the recovery of the native community after alien plant removal.(A) Observational approach, can provide a potential assessment of impacts (B) Experimental approach, can provide a causal assessment of impact, and (C) Experimental approach, provides an assessment of native community recovery after removal of the invader.

Literature search
To The following effect sizes for native species richness and abundance were calculated: X X indicated by p-values associated to Q total higher than 0.05 in most cases (Table 1).Therefore, the magnitude and direction of the effect sizes did not vary significantly across studies, making the generality of the results highly consistent.
The meta-analysis revealed an overall significant decline of native species richness and abundance after invasion.Invaded plots had lower native species richness and abundance than usually adjacent reference noninvaded plots (Fig. 2, Table 1).The same trend was found when comparing invaded versus removal plots (Fig. 2, Table 1).On average, invaded plots contained 23% fewer native species than non-invaded plots and 30% less species than removal plots (Table 1).Invaded plots were 41% less abundant in on the response variable.Data were analysed using random-effects models (P random ) which are preferable in ecological data synthesis because their assumptions are more likely to be satisfied (Rosenberg et al. 2000).A cumulative effect size (R+) is considered significant (i.e.no change with invasion or removal) when its 95% CI do not overlap zero.
Confidence intervals were calculated using bias-corrected bootstrap resampling procedures (Adams et al. 1997;Rosenberg et al. 2000).The mean percentage of change in a response variable was estimated as (e R+ -1) x 100 (Table 1, Appendix I).

Results and Discussion
In general, across all studies, results were quite homogeneous as  1).For none of the response variables evaluated and none of these comparisons, the CI of the mean effect size overlapped zero (Fig. 2).Therefore, our review supports that alien plant species has a negative impact on Native abundance ( Native abundance ( Native abundance ( et al. 2005).However, to consider that a removal effort has Abstract Given the potential ecological impacts of invasive species, removal of alien plants has become an important management challenge and a high priority for environmental managers.To consider that a removal effort has been successful requires both, the effective elimination of alien plants and the restoration of the native plant community back to its historical composition and function.We present a conceptual framework based on observational and experimental data that compares invaded, non-invaded and removal sites to quantify invaders' impacts and native plant recover after their removal.We also conduct a metaanalysis to quantitatively evaluate the impacts of plant invaders and the consequences of their removal on the native plant community, across a variety of ecosystems around the world.
Figure 1 is used as a guide to answer the following questions: (1) Does alien plant invasion decrease native species richness and abundance (Comparison A)? (2) Do alien plant removal increase native species r i c h n e s s a n d a b u n d a n c e (Comparison B)? and finally, (3) Does removed sites resemble to reference non-invaded sites (Comparison C)?

Figure 2 :
Figure2: Mean effect size (R+) of differences in native species richness and abundance between A) invaded versus non-invaded, B) invaded versus removal and C) removal versus non-invaded plots.These comparisons are described in Fig.1.The bars around the means denote bias-corrected 95%-bootstrap confidence intervals.A mean effect size is significantly different from zero when its 95% confidence interval do not overlap zero.Positive and negative mean effect sizes indicate, respectively, an increase or decrease of the response variable following treatment (invasion in comparisons A and B, and removal in comparisons C).The sample sizes are given next to each variable.

Table 1 :
Total heterogeneity (Q t ) with indication of P-values, mean effect sizes (R+), degrees of freedom (df) and 95%-CI for each response variable and type of comparison.Significant results of Q t are in bold.The percentage of change of each response variable with invasion or removal is also indicated.See text for a detailed description of statistical analysis.