Atlantic heath vegetation at its northern fringe in Central and Northern Norway
Tveraabak, Liv Unn
This study emphasises Calluna vegetation on the lowland heaths along the coastline of north Trøndelag and Nordland, middle Norway, the northern fringe of the Atlantic coastal section. Four locations connected to old farming activity were examined through 387 sample plots. Twinspan analysis distinguished five vegetation units: the Calluna-Erica tetralix unit, the Calluna-Myrica-Molinia unit, the Calluna-Racomitrium unit, the Empetrum-Calluna unit with Vaccinium and the Empetrum-Calluna unit with grass and herbs. The geographical distribution shows a south-north gradient with the Calluna-dominated vegetation units at the two southern localities, and Empetrum-Calluna-dominated vegetation types increasing northwards. Direct and indirect ordination (CANOCO) shows that the vegetation changes are associated with both temperatures and humidity. Most important is the decline of the mean winter temperature resulting in shorter growing season and more snow. These five vegetation units were compared with earlier descriptions of related heath vegetation from anthropogenic Calluna heaths and from natural alpine and subarctic Calluna heaths. Indirect ordination shows that the units were most related to man-made Calluna heath vegetation types from the nemoral/boreonemoral zones and the south and middle boreal zones, and less to the natural alpine/subarctic vegetation types. The vegetation units from this study show affinities to five phytosocoiological alliances: E ricion tetralicis Schwick 33, Calluno-Genistion Duvigneaud 44, Empetrion boreale Bøcher 43, Loiseleurio-Arctostaphylion Kalliola 39 and Vaccinio-Piceion Br.Bl. et al. 39.