Alvar

An alvar is a distinctive physical environment formed on a flat limestone plain that carries thin soil or none at all, producing sparse, prairie like grassland rather than forest. The bare limestone surface is often flooded in spring and then dries out under summer drought, a stressed cycle shared by most alvars, which occur mainly in northern Europe and around the North American Great Lakes. This exposed bedrock setting supports a distinctive community of rare plants and animals, including species more typical of open prairie, along with common lichens and mosses, while trees and shrubs are largely absent or stunted.