The structure of calcareous grassland plant communities at different scales: a study from the South Downs, Sussex, UK

摘要

In this article, we examine nestedness and document the plant community patterns and species richness of calcareous grassland on the South Downs, Sussex, UK. The calcareous grasslands of the South Downs are internationally important, and are made up of an intimate mix of grasses, forbs and bryophyte species in close proximity. Analysis of plant community structure and composition can promote understanding and assist in the development of recommendations for conservation and enhancement of unimprovedand semi-improved calcareous grasslands. Initially, species frequency data was used to analyse distribution at the site scale. The paper then examines the interrelationships between rare/scarce, intermediate and core species at the quadrat and site levels, and in relation to grassland area. Plant communities were found to be structured, and the patterns found at the quadrat level were carried through, in modified form, to the site levels. A strong relationship was found between relative abundance/frequency of occurrence at the quadrat level and that observed at the site level. Finally, the patterns in community structure are explained in terms of nestedness, and their applicability to conservation and enhancement of internationally important grasslandhabitats.