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.

[3] This stressed habitat supports a community of rare plants and animals, including species more commonly found on prairie grasslands.

[4] The habitat also has strong competition gradients, with better competitors occupying the deeper soil and excluding other species to less productive locations.

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.

Here the thin soil mantle is only 0.5 to 2.0 centimeters thick in most places and in many extents consists of exposed limestone slabs.