| The shoreline landscapes of many lakes in the northern United States have changed substantially over the past century, but the impacts of these changes on the lakes' aquatic plants are largely unknown. In this study, changes in the macrophyte composition and lakeshore land use of thirty northern Wisconsin lakes are examined at different temporal and spatial scales.; At the whole-lake scale, comparisons were made between 1930s historical data (aerial photos and macrophyte inventories) and contemporary photos and plant inventories done in the 2000s. Land use surrounding the lakes changed through loss of closed canopy woodlands and increased residential land use. This residential development, along with changing sediments, was associated with a doubling of macrophyte species richness, primarily through gains in elodeid species. This shifted the ratio of small-stature isoetid species to large-stature elodeids, altering the structure of the submersed plant community.; The effects of these changes were also examined at the plot-level (1-m x 1-m plots). The percentage of isoetid plots that had elodeids present was associated with conductivity and with the number of elodeid species gained in a lake since the 1930s. Lower cover and species richness of isoetids in the presence of elodeids suggests that elodeids may affect isoetid viability.; The influence of land use on within-lake macrophyte distribution was also evaluated on these lakes. Increased residential density reduced floating-leaf plant cover at both the local and lake-wide scale. However, where natural lakeshore vegetation was retained at residential sites, floating-leaf plants were not affected.; This study found associations between lakeshore land use and aquatic plant composition that have implications for monitoring, management, and conservation, particularly for oligotrophic lakes undergoing change. Monitoring recommendations include using historical baselines, assessing changes in land use and sediment composition, and tracking macrophyte changes with isoetid-elodeid ratios, elodeid immigrations, colonization of isoetid plots by elodeids, and cover of plant functional groups. Recommended strategies for protecting macrophyte habitat include linking allowable shore land alterations to whole-lake development levels, reducing littoral zone disturbance (erosion control, shore land zoning, boating use regulations), and preserving regional habitat (lake classification and protection ordinances). |
