Studies in the floristic diversity of Durham walls, 1958-2008

摘要

A study of the flora of the walls of Durham City over the period 2006-2008 indicated that the floristic diversity had increased by between 39% and 42% since a survey undertaken fifty years ago by Woodell & Rossiter (1959). In addition, the increased frequency 017 Occurrence of twenty-four of the thirty-four key species from the first survey is apparent and there is group of seven species not recorded in the first survey that has become especially prevalent. The increases may be interpreted in terms of the amelioration of the atmospheric environment which has offset any potential reduction of diversity associated with gentrification of the city. An influx of native species has been mainly responsible for the rise in diversity, though the number of neophytes has increased by almost a third of the original total. The floristic diversity of the urban wall habitat is higher than that of rural settlements of the Durham Dales, emphasising the importance of the former as a refuge for many species which have been perceived as declining at the national scale. The walls of each rural settlement have a distinct floristic signature, but the main chasmophyte communities show close phytosociological affinities with the alliance Cymbalarion-Asplenion.