Spread and genetic relatedness of native vs. introduced Phragmites australis in Utah wetlands

Utah is experiencing a dramatic invasion of an aggressive European subspecies of the common reed (Phragmites australis subsp. australis). This invasion is threatening recreation resources, wildlife habitat, and native wetland ecosystems. In this study, we used genetic tools to determine how, and to what extent, introduced Phragmites is spreading among major Utah wetlands. We also assessed native Phragmites (Phragmites australis subsp. americanus) spread to put our introduced Phragmites results in context. In addition, we determined if native Phragmites is being replaced by introduced Phragmites and if the two subspecies are hybridizing. Our results indicate that introduced Phragmites is effectively reproducing and dispersing through both rhizomes and seed but compared with native Phragmites, seems to be spreading largely by seed. Also, we found that levels of gene flow among Utah wetlands is quite high for introduced Phragmites, especially compared with the limited gene flow we found among native Phragmites populations. We found no evidence that native and introduced Phragmites are hybridizing, even where they coexist. In most locations, native Phragmites is not being replaced by introduced Phragmites. However, at Utah Lake, both subspecies co-occur and native Phragmites may be replaced by introduced Phragmites if it is not already. Based on our findings we recommend: (1) that control and prevention efforts for introduced Phragmites should target both forms of dispersal but focus on seeds and (2) that managers carefully monitor locations like Utah Lake, where the two subspecies are co-occurring, to prevent loss of native to introduced Phragmites