Floristic Analyses of British Mires and Mire Communities

Abstract

Floristic data were collected from 40 quadrats (1 .times. 1 m) at each of 56 mire sites in Great Britain [UK]. These data were used to derive ordination scatter diagrams (using reciprocal averaging) and classification hierarchies (using indicator-species analysis) at site and community levels of differentiation. Ordination of the sites showed a major line of variation from ombrotrophic mires with acid waters and peats to geotrophic sites with circumneutral waters and peats. Classification of individual quadrats to produce floristically similar units (noda) revealed a major line of variation, from those noda found in the most acid peats to those of more basic, mineral-enriched locations. The change from one extreme to the other was mostly continuous, with a number of noda containing common species, the proportions of which varied from one nodum to another. By combining site and nodum data, the changes taking place between the extremes were examined. In the most acid and the most basic sites there were high proportions of quadrats falling into a few noda, but in the intermediate sites a large number of noda were represented, each by few quadrats. A series was produced which linked floristic classifications on the basis of species-content of sites and the proportions of different communities (noda) within sites, and related these to hydromorphological mire types and overall chemical conditions, as indicated by pH. By the use of the classification keys produced by indicator-species analysis, new sites may be fitted into this graded series without recourse to re-analysis of the full data-set for all sites. The assigning of a new site to indicate its relationships with other British mires may be by use of species-content of the site as a whole, or on the basis of the proportions of different noda present within that site. Mire bryophytes and other vascular plants were discussed.