Role of black alder (Alnus glutinosa) in vegetation dynamics in West Norway

Abstract

In Norway black alder (Alnus glutinosa) has an ‘optimal’ area along the western coast where it acts as a pioneer species in secondary successions on Calluna and grass heaths, pastures, formerly cultivated land and in hydroseres. Black alder is dominant or co–dominant with birch in oligotrophic grazing forests, most of which belong to the ass. Corno suecicae–Betuletum where black alder seems to be able to survive for a long time. It is also found in a variety of other woodland communities, some of which are stable Alnetea glutinosae or Alno–Padion communities. Others are successional stages towards meso– or eutrophic deciduous forests. The new Alnetea glutinosae ass. Carici nigrae–Alnetum glutinosae is described. The ecology of black alder in West Norway is compared to its ecology in other areas, especially on the British Isles. The humid climate and recent changes in agricultural practice are the main reasons for the present abundance of black alder in West Norway.