An alvar is a biological environment based on a limestone plain with thin or no soil and, as a result, sparse vegetation. It is also known as a pavement barren although this term is also used for similar landforms based on sandstone. In the United Kingdom the exposed landform is called a limestone pavement and thinly covered limestone is known as calcareous grassland. This challenging 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. Alvars can be found in southern Sweden, northwest Estonia and around the Great Lakes in Michigan, New York and Ohio in the United States and in Ontario and Quebec in Canada. Alvars comprise a small percentage of the Earth’s ecosystems by land extent; although some 120 exist in the Great Lakes region, they comprise only 0.2% of the land area there.
In North America, alvars provide habitat for birds such as Bobolinks, Eastern Meadowlarks, Upland Sandpipers, Eastern Towhees, Brown Thrashers and Loggerhead Shrikes whose habitat is declining elsewhere. Rare plants include northern bog violet, balsam squaw-weed, Kalm’s lobelia, Pringle’s aster, Juniper sedge (Carex juniperorum), Lakeside daisy (Hymenoxys acaulis), Ram’s-head Lady’s-slipper (Cypripedium arietinum) and Dwarf Lake Iris (Iris lacustris). Also associated with alvars are rare butterflies and snails.
European alvar locations
Öland – Stora Alvaret – largest alvar extent in Europe
Västergötland – several locations on limestone mountain Kinnekulle, smaller fragments on Falbygden, e.g. in Dala and Högstena parishes.
Alvars are distributed along the whole northern cost of Estonia from approx. the town of Paldiski to Sillamäe, wherever limestone comes to the surface near the seashore (see Baltic Klint), as well as on the islands of the West Estonian archipelago. Estonia used to be home to approximately one third of the world’s alvars, however, the total area of alvars has decreased from 43,000 hectars in the 1930s to 12,000 hectars in 2000, and approximately 9,000 hectars in 2010. Estonian alvars are home to 267 species of vascular plants, approximately one fifth of which are protected. There are also 142 species of bryophytes and 263 species of lichens. The Estonian government has committed itself to protect at least 9,800 hectars of the country’s alvars as part of the Natura 2000 network.
Cumbria and North Yorkshire – under protection in the UK Biodiversity Action Plan
The Burren, a large alvar in northwest County Clare
The use of the word “alvar” to refer to this type of environment originated in Scandinavia. The largest alvar in Europe is located on the Swedish island of Öland. Here the thin soil mantle is only .5 to 2.0 centimeters thick in most places and in many extents consists of exposed limestone slabs. The landscape there has been designated a UNESCO World heritage site.
Stora Alvaret, Öland – Largest alvar extent in Europe.