. The Canadian field-naturalist. Natural history. The Canadian Field-Naturalist. Volume 109, Number 2 April-June 1995 A Review of the Alvars of the Great Lakes Region: Floristic Composition, Biogeography and Protection m Paul M. Catling, and Vivian R. Brownell 2326 Scrivens Drive, 3, Metcalfe, Ontario KOA 2P0 Catling, Paul M., and Vivian R. Brownell. 1995. A review of the alvars of the Great Lakes region: Distribution, floristic composition, biogeography, and protection. Canadian Field-Naturalist 109(2): 143-171. Alvars are naturally open areas of thin soil over essentially flat limestone
. The Canadian field-naturalist. Natural history. The Canadian Field-Naturalist. Volume 109, Number 2 April-June 1995 A Review of the Alvars of the Great Lakes Region: Floristic Composition, Biogeography and Protection m Paul M. Catling, and Vivian R. Brownell 2326 Scrivens Drive, 3, Metcalfe, Ontario KOA 2P0 Catling, Paul M., and Vivian R. Brownell. 1995. A review of the alvars of the Great Lakes region: Distribution, floristic composition, biogeography, and protection. Canadian Field-Naturalist 109(2): 143-171. Alvars are naturally open areas of thin soil over essentially flat limestone or niarble rock with a more or less sparse vegeta- tion cover of shrubs and herbs with trees absent or at least not forming a continuous canopy. Drought and extremes of soil moisture are major factors limiting tree cover. Alvars are important as sites for (1) the protection of biodiversity including threatened plant communities, rare and threatened species of flora and fauna, and germplasm of crop relatives; (2) biologi- cal research and environmental monitoring; and (3) ecotourism. Approximately 85% of alvar sites and more than 90% of alvar landscape area in the Great Lakes region is in southern Ontario. With the exception of small isolated areas, most notably western Lake Erie and Lake Champlain area, the alvars of the Great Lakes region occur near the contact line of the granitic Canadian Shield upland with the Ordovician and Silurian limestones and dolomites. The main area of occurrence extends from the north shore of Lake Michigan east to the islands of northern Lake Huron, such as Drummond Island, east across Manitoulin Island, southeast to the south end of Georgian Bay, east to the Lake Simcoe area and the Garden lime- stone plain, discontinuously east to the Napanee limestone plain between Trenton and Kingston, then, following a gap due to the Frontenac axis of granitic rocks, and/or Lake Ontario, appearing again in New York State at the east end of Lake Ontario and on
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