VEGETATION, ENVIRONMENTAL CHARACTERISTICS AND IDEAS ON THE MAINTENANCE OF ALVARS ON THE BRUCE PENINSULA, CANADA

Despite international recognition that alvar habitats are important re servoirs of biodiversity, they remain little studied in North America. In this paper, the results are reported on an investigation of alvars in the central portion of their known distribution on this continent. 210 plots were distributed among seven sites and were quantitatively sampled for vascular plants, lichens, bryophytes and a suite of enviro nmental variables. Detrended and Canonical Correspondence Analyses and other methods were used to investigate differences among alvars, with in alvars and between alvars and adjacent forested habitats. The plant communities and environmental conditions were highly similar among si tes in the study region, yet very different from surrounding habitats. There were abrupt changes in vegetation and environmental conditions from alvar to forest, without the presence of transition zones in the vegetation or environmental gradients as the forest was approached. Th e environmental factors associated with the change from alvar to fores t and with variation within alvar habitat were examined. Some alvars i n the study were found to contain stunted, slow-growing trees reaching ages of 524 yr. These same sites appear to have remained unburned for several centuries, while other sites Likely burned 90 yr ago. The pla nt communities were very similar between the alvars that lacked a majo r, biomass-removing disturbance in centuries and alvars that had exper ienced catastrophic fire relatively recently. Maintenance of the plant communities and open nature of alvars appears site-specific rather th an habitat specific.