Alvar

An alvar is a biological environment based on a limestone plain with thin or no soil and, as a result, sparse grassland vegetation. Often flooded in the spring, and affected by drought in midsummer, alvars support a distinctive group of prairie-like plants.^[1] Most alvars occur either in northern Europe^[2] or around the Great Lakes in North America.^[3] This stressed habitat supports a community of rare plants and animals, including species more commonly found on prairie grasslands. Lichen and mosses are common species. Trees and bushes are absent or severely stunted.

The primary cause of alvars is the shallow exposed bedrock. Flooding and drought, as noted, add to the stress of the site and prevent many species from growing.^[1] Disturbance may also play a role. In Europe, grazing is frequent, while in North America, there is some evidence that fire may also prevent encroachment by forest.^[4] The habitat also has strong competition gradients, with better competitors occupying the deeper soil and excluding other species to less productive locations.^[5] Crevices in the limestone provide a distinctive habitat which is somewhat protected from grazing, and which may provide habitat for unusual ferns such as Pellaea atropurpurea. Bare rock flats provide areas with extremely low competition that serve as refugia for weak competitors such as the sandwort Minuartia michauxii and Micranthes virginiensis. In a representative set of four Ontario alvars, seven habitat types were described. From deep to shallow soil these were: tall grassy meadows, tall forb-rich meadows, low grassy meadows, low forb-rich meadows, dry grassland, rock margin grassland and bare rock flats.^[6]

Alvars comprise a small percentage of the Earth's ecosystems by land extent. Although some 120 exist in the Great Lakes region, in total there are only about 43 sq mi (110 km²) left across the entire Great Lakes basin, and many of these have been degraded by agriculture and other human uses. More than half of all remaining alvars occur in Ontario. There are smaller areas in New York, Michigan, Ohio, Wisconsin and Quebec.^[7]

In

• Sweden
  • Öland – Stora Alvaret – largest alvar extent in Europe
  • Gotland
  • Västergötland – several locations on limestone mountain Kinnekulle, smaller fragments on Falbygden, e.g. in Dala and Högstena parishes
• Estonia
  • Alvars are distributed along the whole northern coast of Estonia from approx. the town of
    Estonian government has committed itself to protect at least 9,800 hectares of the country's alvars as part of the Natura 2000 network.^[14] The Loopealse subdistrict of Tallinn
    is named after alvar.
  • Vardi Nature Reserve in Rapla County is an Estonian nature reserve especially designated to protect one of the more representative alvar areas of Estonia.
• England
  • Biodiversity Action Plan
• Ireland
  • The Burren, a large alvar in northwest County Clare

• 
  Sarve alvar in Hiiumaa island
• 
  Alvar in

  Väike-Pakri

  island
• 
  Sparse vegetation, Kinnekulle, Sweden
• 
  Limestone pavement at Malham Cove, UK

Some North American alvar locations

• The rare Charitable Research Reserve – Cambridge, Ontario^[15]
• Lake Erie
  • Kelley's Island, Ohio – North Shore Alvar State Nature Preserve^[16]
  • Marblehead, Ohio – mostly destroyed by limestone quarrying
  • Pelee Island, Ontario – Stone Road Alvar Nature Reserve^[17]
• Lake Huron
  • Maxton Plains Proposed Natural Area,
    Drummond Island, Michigan^[18]
  • Belanger Bay Alvar, Manitoulin Island, Ontario^[19]
  • Quarry Bay Nature Reserve, Manitoulin Island, Ontario^[20]
  • Bruce Alvar Nature Reserve, Bruce Peninsula, Ontario^[21]
  • Baptise Harbour Nature Reserve, Bruce Peninsula, Ontario^[22]
  • Misery Bay Provincial Park, Manitoulin Island, Ontario^[23]
• Lake Michigan
  • Red Banks Alvar, Red Banks, Brown County, Wisconsin^[24]
• Lake Ontario
  • Carden Plain Alvar, City of Kawartha Lakes, Ontario, including Carden Alvar Provincial Park^[25]
  • Chaumont Barrens Preserve, New York^[26]
  • Three Mile Creek Barrens, New York
  • Burnt Lands Alvar, Almonte, Ontario
  • Balsam Lake Indian Point Provincial Park, Ontario^[27]
• Quebec
  • Quyon
  • Alvar d'Aylmer^[28]
• Manitoba
  • Interlake^[29][30][31]

See also

• Calcareous grassland – An ecosystem associated with thin basic soil
• Chalk heath
• Edaphic
   – Science concerned with the influence of soils on living beingsPages displaying short descriptions of redirect targets
• Gypcrust – Hardened layer of soil with a high percentage of gypsum
• Gypsum flora of Nova Scotia – Group of plants in Nova Scotia, Canada
• Rendzina – Humus-rich shallow soil type
• Barren vegetation – Area of land where plant growth may be limited

References