Decline of moorland plants following the establishment of a Scots pine plantation

Summary

A tract of heather (Calluna vulgaris) moorland on a brown-earth soil in north-east Scotland was planted with Scots pine in 1974, and the subsequent changes in heather and botanical composition were monitored. The pines established well and attained a mean girth of 37 cm by 1995. Before planting the moorland was heavily grazed by sheep which kept the heather short (mean height 7 cm) but with high cover (71%). After planting there have been three phases in the development of the ground vegetation. In the first eight years the heather benefited from the cessation of grazing, reaching 17 cm height and 89% coverin 1982. The cover of pine remained less than 5%, but grasses declined significantly in cover and some forbs became extinct e.g. Lotus corniculatus. In the second 8-yr phase the pine canopy closed but heather retained its dominance still having 89% cover in 1990 and a mean height of 20 cm. The main change in composition was a decline in the subsidiary dwarf shrubs (Arctostaphylos uva-ursi, Erica cinerea and Genista anglica), but grass cover was further reduced and more angiosperms became extinct. After 1990 there was rapid death of heather and a reduction in bryophyte cover, causing the extent of bare ground to increase. By 1995 the combined cover of all vascular plants had fallen to 17%, and only Deschampsia flexuosa, Festuca ovina, Trientalis europaea and Vaccinium vitis-idaea seem likely to survive the intense shade of the thicket stage. Differences between the present flora and that of second-rotation and native pinewoods are discussed.