Nordic alvar and precambrian calcareous flatrocks

Description (English)

Nordic alvar and Precambrian calcareous flatrocks are very species-rich ecosystems, with an ecological character strongly influenced by winter climatic conditions. When a thin soil layer exists, it is often frozen to ice and covered with snow. Plants and animals have special adaptations to these conditions. For example the invertebrates must have strategies for overwintering. Annual freezing and thawing give rise to movements at the soil surface creating small patches of bare soil occupied by annual plants, a number of which are rare. The flat rocks may be covered with a thin layer of soil, which is the product of weathering of the underlying rock. The flora and fauna is very rich on species and many of them are rare. On Öland the Nordic alvar represents a subtype with dominating Helianthemum oelandicum and other endemic species. The ground is covered with a 5-30 cm deep crumbling soil. The inclination is near zero and the draining process is extremely slow. Freeze-thaw action creates soil polygons with a characteristic patterning of vegetation. In Nordic alvar there are also depressions, which sometimes are filled with water. In summertime those wetlands, on Öland and Gotland called “vätar” , will dry up - completely or partially. Nordic alvar is a habitat type of cambro-siluric or precambrian calcareous rocks.