The Ecology of the Cairngorms: Part II. The Mountain Callunetum

Abstract

In the Cairngorm mountains (Scotland) the Mountain Callunetum forms a belt of vegetation between 670m. and 970m. The Calluna forms a short turf about 5 cm. high formed by the interweaving of prostrate stems. The associated flora on the acid sandy soil is poor in spp. The principal arctic-alpine spp. are Arctostaphylos uva-ursi, Loiseleuria procumbens, Empetrum hermaphroditum, Juncus trifidus, Carex bigelowii, Lycopodium alpinum. Much Cladonia rangiferina is anchored in the turf. These spp. occur in patches forming a characteristic pattern which is dependent on local topographic factors (terracing, etc.). At the lower limit the community merges into wet Calluna heath; at the upper limit ecotones with Empetreto- Vaccinietum occur in less exposed situations and with Juncetum trifidi in more exposed. Calluna ascends higher on exposed ridges (to 970m.) than in sheltered situations with longer snow cover (ca. 920m.). The lower limit of L. procumbens is 610m., of J. trifidus, 730m., the upper limit of A. uva-ursi, 790m. Callunetum is replaced by Vaccinietum or Nardetum where there is long snow cover. On eroded ground and in closed vegetation, Calluna and Arctostaphylos are in constant cyclical competition. On eroding ground Calluna grows in strips separated by areas of eroding soil; Calluna and Arctostaphylos colonize the bare ground at the front of each wave and are overwhelmed behind. The plants and the habitat form an interacting complex which results in the formation of step-like terraces.