BIODIVERSITY IN MONTANE BRITAIN - HABITAT VARIATION, VEGETATION DIVERSITY AND SOME OBJECTIVES FOR CONSERVATION

The montane (low- to mid-alpine) zone in Great Britain (GB) lies above the potential tree-line (700-800 m, but descending to 200 m in the north). It is composed of moss and lichen heaths, snowbeds, blanket bog and dwarf-shrub (Ericaceae) health-covered solifluction/gelifluction terraces (38 communities/sub-communities). Approximately 3.0% of the land surface is covered by this - the most extensive predominantly near-natural terrestrial habitat in GB. Internationally distinctive features include oceanic and southern biotic outliers of arctic-alpine fellfield and mountain tundra, and plant communities that are either globally rare/localised or especially well represented in GB. The absence of extensive sub-alpine Betula spp. and Salix spp. scrub is striking. The main sources of habitat diversity are climate, regional variation in topography and geology, and regional modifications due to land-use impact. Over 50 examples are given. Five important gradients in Scottish Highland vegetation are described. Only some 15% of the sampled montane vegetation is anthropogenic; the rest is semi- or near-natural. The vegetation is divided into 5 functional groups: chionophobous (avoids snow), chionophilous (prefers snow), species-rich, mires (including springs and flushes), and anthropogenic. Chionophobous and then chionophilous communities contribute most to montane vegetation diversity (calculated here as the Shannon H diversity index). H diversity increases asymptotically with montane site area but linearly with the number of communities present. A more varied topography, geology and topo-climate gives the highest H diversity. Two examples of montane biodiversity reductions south of the Highlands are the loss of prostrate Calluna vulgaris heaths and modification of Racomitrium lanuginosum heaths. Five objectives for nature conservation are proposed, covering restoration of montane R. lanuginosum heaths, prostrate dwarf-shrub dominated heaths, sub-alpine scrub and upper treelines, and the extension of the breeding ranges of both ptarmigan (Lagopus mutus) and dotterel (Charadrius morinellus) south of the Scottish Highlands. International support for monitoring is sought.