See his complete works, ed. by K. Fleig (tr. of 3d ed., 2 vol., 1970-71); studies by F. A. Gutheim (1960) and P. D. Pearson (1978).
An alvar or pavement barren is a biological environment based on a limestone plain with thin or no soil and, as a result, sparse vegetation. In the United Kingdom this landform is called a limestone pavement. 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.
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.