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.
Effective suppression of established invasive Phragmites australis leads to secondary invasion in a coastal marsh
