A review of the use of plant community data for assessing ecological quality

The use of community data for the assessment of quality is best developed in freshwater ecology. Methods such as RIVPACs use statistical relationships between environmental covariables and classifications of reference site communities to assess the relative quality of new sites. Although such ‘RIVPAC-like’ approaches can be conceived of for plant communities, existing sets of data most likely to be appropriate for defining reference sets (e.g. the NVC relevés) lack corresponding sets of environmental data. Environmental data could be extrapolated from extant high quality stands or remote-sensing data, but such approaches seem likely to lead to lower discriminatory ability as compared to actual co-located data. Other options include the 2007 Countryside Survey, which collected co-located environmental data but may not be representative of SSSI-quality habitat features, and the NPMS, which was purposefully biased towards higher quality sites, but which has not so far collected environmental data likely to be of use in a RIVPAC-like approach. Alternative approaches to assessing quality involve community data in isolation. That is, newly collected plant community data could be compared to reference sets denoting high and low ecological quality for a given habitat through multivariate methods such as classification and ordination. Challenges for this approach include: the selection of the reference samples to be used for any given habitat feature (potentially also taking into account regional variation); for ordination approaches, the number of axes to be assessed as part of a quality assessment, and how movement along these axes is assessed; and, for classification, the choice of clustering method to be used. ‘Fuzzy clustering’ in particular is increasingly used to derive measures of fit of new vegetation samples to existing reference classifications.