Recent Invasion, Current Status and Invasion Pathway of European Common Reed, Phragmites australis subspecies australis, in the Southern Ottawa District

Résumé

A survey of populations of native North American Common Reed (Phragmites australis subsp. americanus) and the introduced invasive alien, European Common Reed (Phragmites australis subsp. australis) was conducted in four eastern Ontario townships in 2003. The historical status of the two taxa in the region was evaluated through reference to herbarium specimens collected over the past century. The introduced subspecies appears to have entered the district in the 1970s and subsequently assumed dominance but was not recognized as an alien until 2003. It is now widespread in the four townships where ninety-five populations were recorded during the 2003 survey. Of these, 25 were referable to the native subspecies which was localized and 70 were referable to the introduced subspecies which was widespread. The native subspecies occurs in natural wetlands and also spreads to roadsides, but the introduced subspecies is much more strongly associated with roads, where the rhizomes extend onto gravel shoulders and are broken and transported by construction equipment, graders, ploughs, mowers, and in the treads of many kinds of vehicles. Sensitive wetlands should have buffer zones exceeding 1000 m to prevent colonization of subsp. australis. Monitoring of the two subspecies will be essential to the protection of native biodiversity, since early detection of the alien subspecies in a sensitive wetland will offer the best opportunity for control.