THE ROLE OF SEED BANKS IN THE PERSISTENCE OF ONTARIO'S COASTAL PLAIN FLORA

Abstract

Seed banks are important in wetland vegetation, but their role on lakeshores has received little attention. The influence of seed banks on lakeshore vegetation was investigated near eastern Georgian Bay in Ontario, where there is a rich shoreline and aquatic flora. Some lakeshore species found there can be considered “coastal plain disjuncts” similar to those of southwestern Michigan and adjacent Indiana, and central Wisconsin. Matchedash Lake in Simcoe Co., Ontario, has a particularly rich assemblage of these shoreline species. Based on short‐term records, and aging of drowned stumps, we demonstrated that yearly mean water levels can and have changed by more than a meter. Such water‐level fluctuations partly result from beaver dams on the single outlet stream. Vegetation data collected in a low‐water phase (1976) document a rich shoreline flora, largely absent in the present (1979) high‐water phase. During this latter high‐water phase, we collected 15 sediment sample units from each of six water depths (0–1.5 m). The sample, representing 0.32 m 2 of lake bottom, was planted out in a greenhouse; 3,149 seedlings representing 41 species of vascular plants emerged. Six (Rhexia virginica, Rhynchospora capitellata, Panicum spretum, Xyris difformis, Polygonum cureyi, Linum striatum) are rare in Ontario. Estimated seed banks for individual species were as high as 6,500 seeds m“2. If another low‐water phase occurs, a rich shoreline flora should again develop. We hypothesize that water‐level fluctuations are essential to the long‐term survival of these species.