Alvars of Ontario

Alvars are naturally open habitats with either a thin covering of soil or no soil over a base of limestone or dolostone. Globally, alvars are restricted to the eastern European Baltic region and the North American Great Lakes Basin. North American alvars support a distinctive set of flora and fauna, and almost 75 percent of these alvars are located in Ontario: Ontarians have a responsibility to conserve these globally significant alvar habitats and their specialized species communities.

The unique geological, post-glacial historic and physical stress characteristics that define an alvar set the stage for interdependant biological communities which simply cannot exist elsewhere. The five main alvar types are alvar shrublands, alvar grasslands, alvar savannas, alvar pavements and alvar woodlands. Many alvars contain a multitude of listed and globally imperilled species, including many rare invertebrates and the globally endangered Eastern Loggerhead Shrike.

Carden Alvar (Photo by NCC)

One of the most fascinating aspects of alvars is that they are among the most species-rich communities in the world at a small scale (<100 cm2). Alvars appear to have a much higher degree of specialist and endemic species than other habitat types in the Great lakes. In particular, the unique conditions in alvars appear to drive evolutionary processes and speciation in invertebrates. One report has estimated that up to 1000 species of insects may be unique to alvar habitats, and several species of terrestrial mollusks are only known from alvar sites.

Carden Alvar was given the highest conservation ranking by the International Alvar Initiative and identified as high significance by a report on Ontario alvars. This alvar is a complex of alvar grasslands, alvar shrubland, treed or partly treed ridges and slopes, and riparian wetlands including excellent quality alvar plant communities such as Creeping Juniper-Shrubby Cinquefoil alvar dwarf shrubland, Poverty Oat Grass dry alvar grassland, Tufted Hairgrass wet alvar grassland, and Juniper alvar shrubland.

Alvar Grike with Maidenhair Spleenwort (Photo by NCC)

The Northern Bruce Peninsula and Manitoulin Island support some of the best examples of irreplaceable alvar habitat in the world and are key areas for alvar conservation in North America. These areas boast Ontario's best examples of alvar pavement, which consists of exposed rock with lichen and moss communities dominating the flora. Other plants, such as Early Saxifrage and Maidenhair Spleenwort, take root in the grikes, joint fractures in the limestone shaped by water erosion.

Pelee Island Alvar Savanna (Photo by NCC)

Stone Road Alvar on Pelee Island is designated as a provincially significant Area of Natural and Scientific Interest (ANSI). The site is a globally unique limestone plain or alvar not represented elsewhere in Ontario and is disjunct from other limestone plains in the Great Lakes basin by several hundred miles. Over 50 provincially rare plant species have been recorded at Stone Road Alvar, making it one of the most botanically significant sites in Ontario. Because of fire suppression on the island, some alvar communties are dominated by shrubs, excluding many of the globally rare species that require open alvars. Conservation ownership and stewardship will ensure appropriate long-term management and conservation of alvars on Pelee Island.

The Napanee Plain also contains alvar ecosystems which support incredibly rare species such as the globally, nationally and provincially rare as well as endangered Juniper Sedge.