Executive Summary
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.
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.