CHANGES IN THE EXTENT AND FRAGMENTATION OF HEATHLAND AND OTHER SEMINATURAL HABITATS BETWEEN 1920-22 AND 1987-88 IN THE LLYN PENINSULA, WALES, UK

Habitat modification is assessed over a period of 20th century agricul tural expansion in the Llyn Peninsula, a coastal district on the weste rn oceanic fringe of Britain. Habitat area data were derived from vege tation maps produced by surveys in 1920-22 and 1987-88. These are comp ared to assess the extent and nature of habitat change and degree of f ragmentation. There was an over-all depletion of 3 629 ha (44%) of sem i-natural habitat, mostly due to conversion to agricultural grassland in low-lying areas. The major reductions were in dry heathland (1500 h a, 51%) and especially in wet heathland (1 738 ha, 95%), and there wer e also declines in the areas of scrub, fen and sand dune habitats. The re appear to have been temporary fluxes in some vegetation types, espe cially wet grassland and bracken, and local gains have also offset los ses in deciduous woodland. In many cases, habitat erosion has been acc ompanied by diminution in patch size, and there were fewer large areas of seminatural habitat in the 1980s. Implications for nature conserva tion are discussed, and it is suggested that the larger surviving patc hes should be a focus for priority protection. Possibilities for habit at redevelopment are considered.