Herbicide application as a habitat restoration tool: impact on native island plant communities

Abstract

Questions Which physical or chemical removal method is most effective in controlling woody invasive alien plant (IAP) species in sensitive conservation areas, while minimizing the impact on different life stages of native plant communities? Is there a distinct influence of removal method on successional trajectories of post‐treatment seedling communities? Location Mid‐altitude inselbergs, Mahé, Seychelles, Indian Ocean. Methods We conducted two field experiments. First, to test the effects of four IAP control methods (cut, 5%, 10%, 15% Tordon 101 herbicide concentration) on ten woody IAP species, we treated a total of 320 adults and monitored mortality for 18 wk. Second, we set up five blocks each with four plots (4 m × 4 m) at three inselberg sites (N = 60 plots) and recorded the response of seedlings, saplings and adults of all native and IAP species to four Tordon 101 (a.i. picloram and 2,4‐D) herbicide and manual control treatments (cut, cut‐stump, foliar spray, control) over 22 mo. Treatment effects were analysed with GLMM models, and community responses were investigated with NMDS and multivariate ANOVA. Results The first experiment showed that IAP mortality (98.3%) was similar across all three herbicide concentrations, but markedly higher than mortality of cut plants (42.5%). In the second experiment, abundance, but not diversity, of native seedlings declined with herbicide application in the first 6 mo after treatment. Ordination analysis showed that seedling communities experienced high turnover driven by early successional IAP species and abundance, and that between‐plot variation was determined by site‐specific differences, with only a weak treatment effect. Foliar spray resulted in high mortality of native saplings (52.7%) and adults (18.3%), and both herbicide applications reduced adult growth over a post‐treatment period of 12 mo. Conclusion IAP removal controlled plant invasion processes and altered community composition in the short term, regardless of removal method. Post‐treatment trajectories of seedling communities are determined by site‐specific differences. Chemicals can strongly increase the efficacy of IAP control, but short‐term detrimental effects on native saplings and adults may be expected. As re‐invasion by IAPs is likely, a long‐term restoration plan is required. Management strategies that aim to conserve β‐diversity should employ a landscape approach to habitat restoration to buffer against site idiosyncrasies.

Glyphosate, steam and cutting for non‐native plant control in Alberta fescue grassland restoration

“…() found key native grassland forbs were rare 16 yr after picloram control for non‐native plants, and others found temporary declines in native species richness and diversity (Kaiser‐Bunbury et al. ). When certain species are eliminated they may leave niches that can be filled by other non‐native species (Pearson et al.…”

“…In our study, native forbs did not establish on heavily invaded sites and declined as non-native forbs increased at a less invaded site. Rinella et al (2001) found key native grassland forbs were rare 16 yr after picloram control for non-native plants, and others found temporary declines in native species richness and diversity (Kaiser-Bunbury et al 2015). When certain species are eliminated they may leave niches that can be filled by other non-native species (Pearson et al 2016).…”

“…The response of native plants to management is not well known for most methods. Non-native control methods may only be detrimental to native species in the short term and dependent on timing of management application (Adams et al 2014;Martin et al 2014;Kaiser-Bunbury et al 2015;Munson et al 2015). Simple and cost-effective methods with low effect on native species and high control of non-native species are needed.…”

Seed dispersal by frugivores from forest remnants promotes the regeneration of adjacent invaded forests in an oceanic island

“…1). Between 2011 and 2012, four of the inselbergs were cleared of all non-native plants with the aim to restore native plant communities, while the other four were left with both native and non-native species (Kaiser-Bunbury et al 2015). Irregular maintenance of the "restored" sites resulted in encroachment of previously removed and recently arrived non-native plant species, mainly C. hirta and C. verum (A. Costa personal observation).…”

Impacts of invasive ants on pollination of native plants are similar in invaded and restored plant communities

“…1 ha each on Mahé, the largest granitic island of the Seychelles, Indian Ocean (-4.6953 • , 55.4999 • , 154 km 2 , 900 m a.s.l.). Between 2011 and 2012, all non-native plants were removed from four of the inselbergs to restore plant communities, while the other four sites remained unaltered with both native and non-native species (Kaiser-Bunbury et al, 2015). Hereafter, we refer to sites undergoing restoration as "restored" and sites invaded by non-native plant species as "unrestored".…”