Geographical patterns in the flora of Cambridgeshire (v.c.29)

Cambridgeshire data collected for the BSBI’s Atlas 2020 project include 347,496 records at monad (1 km) or finer resolution. We used these data to cluster taxa by spherical k-means to produce 21 clusters of taxa with similar patterns of distribution. Some of the clusters correspond to well-defined habitats such as chalk grassland, ancient woodland, traditional fenland, and saline riversides and roadsides. Other clusters were less expected, corresponding to arable clayland, washland (the Ouse and Nene washes), waste ground and garden escapes. There was a cluster of ubiquitous species and another of common arable weeds. The distributions of the clusters are displayed as coincidence maps. Some species are intermediate between two clusters. These can be recognised by their relatively poor goodness of fit to any one cluster. The clusters differ markedly in ecological attributes and whether they include rare or threatened species. We interpret these differences using Ellenberg values and the vascular plant Red List for England.