By 'alvar' is meant the flat rocky soils that occur on hard limestone soils in some places in the world. Alvar on Öland is the result of a millennial coexistence between human farming and the natural conditions. Stora alvaret is a habitat for a large number of plants and animals - many very unusual elsewhere.

Alvar is characterized by the fact that they

lacks or has only a thin soil cover,
has a widely changing supply of water,
has a harsh climate and
has a unique plant and animal world.

Alvar similar to the Öland alvar are found on the islands with limestone bedrock in the Baltic Sea, mainly on Gotland, Dagö and Ösel, but small areas are also found in Västergötland.