No abstract

Invasive species negatively impact vegetation communities. Invasive Phragmites australis ssp. australis (European common reed) ((Cav.) Trin. ex Steud) is rapidly spreading throughout North American wetlands. As such, the suppression of P. australis populations is a goal of many managers, as its removal should provide an opportunity to restore native vegetation communities. In Ontario, managers applied a glyphosate-based herbicide to over 400 ha of P. australis in ecologically significant coastal marshes, representing the first time this tool was used over standing water to suppress an invasive species in Canada. Using a Before-After-Control-Impact monitoring design, we evaluated the efficacy of glyphosate-based herbicide at removing P. australis along a water depth gradient and assessed the recovery of the vegetation community for two years after treatment in relation to reference conditions. We found that herbicide suppressed over 99% of P. australis one year after treatment and worked effectively along the entire water depth gradient (10 – 48 cm). However, the post-treatment vegetation community remains distinctive from reference marsh two years after treatment. In many plots where P. australis was removed, non-native Hydrocharis morsus-ranae (European frog-bit) (L.) is now dominant, likely aided by high lake water levels.

No abstract

Robichaud and Rooney. 2020. Glyphosate used to control invasive Phragmites australis in standing water poses little risk to aquatic biota. Pre-print. Contact

Wetland restoration often involves invasive‐plant suppression to encourage the recovery of native‐dominated vegetation communities. However, assessment of recovery is usually focused only on vegetation, and the response of other critical wetland biota, such as macroinvertebrates, is seldom assessed. We characterized the aquatic, semi‐aquatic, and terrestrial macroinvertebrate communities in remnant, uninvaded marsh to identify restoration targets and compared this to the communities in Phragmites australis‐invaded marsh and in the formerly invaded marsh that was treated with the herbicide glyphosate in 2016 to simultaneously evaluate the effects of invasion and invasive‐species suppression. We sampled invertebrates in 2017 and 2018 to track 2 years following herbicide treatment. The invertebrate community composition was similar between P. australis invaded and remnant marsh, suggesting invasion has little effect on macroinvertebrate community structure. There was also high concordance between the aquatic and emerging‐invertebrate communities in the invaded and uninvaded habitats. In contrast, herbicide‐treated sites had a unique community composition, characterized by very high densities of Chironomidae (Diptera) and low taxa richness and evenness. Herbicide‐treated sites also exhibited low concordance between the aquatic and emerging‐invertebrate communities, potentially attributable to the sparse, emergent‐vegetation cover providing limited substrates for emergence. Herbicide‐based, invasive‐species control resulted in considerable changes to the macroinvertebrate community in freshwater marshes for at least 2 years after treatment, which may have consequences for aquatic food webs and species that rely on macroinvertebrates as prey.