A WATERSHED LEVEL ANALYSIS OF THE LAKESHORE PLANT COMMUNITY

An investigation was conducted to determine whether the variables, standing crop and sediment organic matter content, related to species richness patterns at the local level, varied at the landscape level in accordance with differences in lake watershed area. Previous study had demonstrated the importance of watershed area as a predictor of species richness of all herbs and of rarities, in particular, on lakeshores. In this study, the reciprocal of watershed area (log units) accounted for over 75% of the variation in biomass at above and below summer waterline positions. Furthermore, watershed area accounted for most of the variation in sediment organic matter content. Above the waterline, shrubs were the predominant growth form at lakes with small watershed areas; the reciprocal of watershed area accounted for 92% of shrub biomass variation. Shoreline plant communities on the lowest watershed area lake were high-biomass, shrub assemblages above waterline and low-biomass, graminoid communities below the waterline. In contrast, above the waterline but below the upper shrub zone on the high watershed area lake, shorelines supported low-biomass assemblages composed of a mixture of shrubs, graminoids, forbs, and ferns. The strong relationships found here between biomass and organic matter and lake watershed area reconcile predictive models made at the within-lake level with those made at the landscape level.