A NEW BIOGEOGRAPHICAL CLASSIFICATION OF THE SCOTTISH UPLANDS .1. DESCRIPTIONS OF VEGETATION BLOCKS AND THEIR SPATIAL VARIATION

1. A vegetation survey of 88 Scottish upland sites (mainly designated as Sites of Special Scientific Interest) was carried out between 1981 and 1988. Vegetation stands were classified in the field into 90 previ ously defined types, equivalent to 65 communities in the National Vege tation Classification. Vegetation maps were drawn for each site and me asured to give quantitative data on the occurrence and extent of the c ommunities. 2. Two-way indicator-species analysis, used to classify th e sites and communities, gave nine geographical groups of sites, each defined by blocks of indicator communities. These nine groups remained stable when the analysis placed varying degrees of emphasis on commun ities which are rare and restricted (in area) or on extensive communit ies which make up the major components of the upland landscape. 3. The geographical groups summarize the range of ecological variation acros s upland Scotland and can be regarded as a biogeographical classificat ion. Two major biogeographical contrasts were between: (i) the highest and marginally lower sites, and (ii) eastern and western Scotland. Th e greatest contrasts in the diversity of upland communities lie betwee n south-east and north-west Scotland, with particularly low diversity in the Southern Uplands. Low-altitude Calluna vulgaris-dominated sites were found to be similar in all Scottish geographical groups. The gro ups concur with many of the regions of interest that have been previou sly described as being related to climate and geology.