Biogeography of island flora in the Georgian Bay, Lake Huron, Ontario

In this dissertation I analyzed multiple, interrelated variables that affect spatial variation of plant species richness among freshwater islands, and incorporated forest dynamics as a temporal axis to judge the permanence of richness patterns. The study encompassed islands within Ontario\u27s Massasauga Provincial Park in the Georgian Bay (Lake Huron), Canada. Specific objectives of this dissertation were (1) to test the applicability of species-area relationships and species-isolation relationships to insular plant assemblages, (2) to examine the influence of variables other than area and distance on species richness, and (3) to determine whether current patterns of species richness are in a stage of transition. Subsets of species richness (growth form, origin, dispersal mode, and island location) were analyzed to determine whether the results differed from the total data set. Thirty-five islands were sampled in The Massasauga Provincial Park archipelago. Sampled islands were located using stratified random selection based on location and size variation. Species richness and substrate characteristics (pH and depth) were measured along transects on each island. Forest data (e.g. stem counts, diameter measurements, increment cores) were collected in stratified random quadrats along the transects. Island morphology and isolation variables and elevation measurements were calculated with a GIS. Regression analyses were performed to determine which variables best explain patterns of species richness among the islands. The results indicate significant species-area (R 2 = 0.84) and species-isolation relationships (R 2 = 0.24). Although some alternative variables were comparably as important as area, none accounted for more of the variation in richness than area. The best combination of variables included island morphology and environmental heterogeneity (R 2 = 0.91). The explanatory strength of variables differed by subset, revealing patterns that were obscured when using total species richness counts. The majority of islands are dominated by white pine, but size-class distributions suggest that large and/or round islands are likely to shift from pine-dominated stands to pine-oak stands, leading to an increase in species richness