Although much is known about the physiological capabilities of reed canarygrass (RCG) and the consequences of invasion, less is known about the roles that wetland type and surrounding disturbances play in facilitating the spread of RCG in predominantly forested landscapes. Therefore, the goals of our study were to test if (1) certain wetland types in the Northern Great Lakes region were more susceptible to RCG invasion, (2) certain disturbances facilitated RCG, and (3) the level of road development and the presence or absence of a ditch bordering each observed road influences the frequency of adjacent RCG populations. We randomly selected 28 wetlands within the Keweenaw Bay Indian Community reservation in the Upper Peninsula of Michigan. At each wetland, we collected plant community and environmental data and catalogued disturbances. In all, 287 plant species were identified. Cluster analysis revealed 16 distinct vegetation communities, which were distributed among three broader wetland community types: (1) nonforested graminoid, (2) Sphagnum peatlands, and (3) forested wetlands. Occurrence of RCG was most common in the nonforested graminoid communities and was also positively correlated to disturbance. The most frequent disturbances were roads, off-road vehicle trails, and logging activity. Additionally, paved and graded roads, and roads with ditches, were more likely to have RCG alongside them than unpaved dirt roads. Our data suggest that RCG occurrence is controlled by interactions between wetland types and disturbance.
Nomenclature: Reed canarygrass, Phalaris arundinacea L.; Sphagnum spp.
Management Implications: Reed canarygrass (RCG; Phalaris arundinacea) is a widespread invasive species that colonizes wetlands and converts them to near monocultures. Currently, RCG is difficult to remove once established. Therefore, the best control may be to prevent its colonization in new areas. Our results indicate that RCG preferentially invaded certain wetland types more than others. RCG was most likely to invade nutrient-rich graminoid wetlands and shrubby wetlands. RCG did not invade low-nutrient Sphagnum peatlands, and shady forested wetlands were not typically invaded unless the canopy was opened. We also found that RCG density was correlated with disturbance, particularly roadsides and roadside ditches, road development, off-road vehicle trails, and logging activity. Additionally, paved and graded roads were more likely to have RCG alongside them than were unpaved, dirt roads. This indicates that transportation corridors are effective in facilitating the movement of RCG into wetland areas. Additionally, many rich conifer-forested wetlands are normally too shady to have large populations of RCG, but roads, logging activity, walking trails, power lines, pipelines, and other openings were found to open the canopy sufficiently to allow the invasion of RCG. This can have major implications as simple management activities such as thinning or putting in a hiking trail into rich conifer wetlands can facilitate the invasion of RCG into these systems.