|WERSAL, RYAN - Lonza Corporation|
|MARKO, MICHELLE - Concordia College|
Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2016
Publication Date: 9/1/2016
Citation: Madsen, J.D., Wersal, R.M., Marko, M.D. 2016. Distribution and biomass allocation in relation to depth of flowering rush (Butomus umbellatus) in the Detroit Lakes, Minnesota. Invasive Plant Science and Management. 9:161-170.
Interpretive Summary: Flowering rush is an invasive aquatic plant that has established in water resources across the United States and Canada. While research has been done on population genetics, little research has been done on its preferred habitats, adaptation to water depth, or impact on native plant communities. Flowering rush has been established in the Detroit Lakes (MN) since the 1960’s, and become a significant nuisance to shoreline residents and recreationists. In this study, we document that, while flowering rush can occur to depths of 4.8 m (16 ft), it was most abundant to 1.3 m, so management efforts could be targeted from the shoreline to depths of 1.3 m. Flowering rush established in areas that already contained native aquatic plants, including hardstem bulrush, rather than establishing in areas without vegetation. Examining biomass allocation in depths from 0.3 to 3.0 m, biomass and density was highest in depths less than 1.0 m, and decreased significantly beyond 1.3 to 1.6 m. Rhizome buds, the main propagule of flowering rush, had their highest densities from 0.3 to 1.6 m, averaging 200 to 300 N m-2, which translates into 0.8 to 1.2 million buds per acre.
Technical Abstract: The Detroit Lakes chain of lakes consists of five basins in northwest Minnesota, adjacent to the town of Detroit Lakes. Flowering rush has been established in these basins since the 1960’s. We evaluated the distribution of flowering rush in the five basins using a point intercept method, with 830 points distributed in a grid with points 150 m apart. These data were analyzed to determine if invasive and native species frequencies were changing between 2010 and 2011. We also assessed co-occurrence of flowering rush with native hardstem bulrush (Schoenoplectus acutus). The distribution of both flowering rush and hardstem bulrush was unchanged from 2010 to 2011. Flowering rush is invading areas with native plants, and not establishing in unvegetated areas. While flowering rush is found as deep as 3.64.5 m, it is most frequent to a depth of 1.2 m or less. Our second study examined the distribution of biomass and growth across a depth gradient, from 0.3 to 3.0 m in 0.3 m intervals. At each 0.3 m interval, three biomass samples were collected at each of ten transects, for a total of thirty samples per depth interval or three hundred biomass samples. At each point, leaf height, emergent leaf height, water depth, the number of ramets, and the number of rhizome buds were counted. Biomass samples were collected in a 0.018 m2 core sampler, sorted to shoots and belowground biomass. We found that flowering rush height and biomass peaked at 1.3 m, and declines with greater depth. Bud density was negatively correlated with water depth. Bud density averaged 300 N m-2, which was three times the average ramet density (100 N m-2).