Numerical analysis of bryophyte-environment relationships in a lowland English flora

摘要

Presence-absence data for 301 bryophytes within 95 5 x 5 km grid squares of the lowland English county of Berkshire were subjected to ordination and classification employing Detrended Correspondence Analysis (DCA), Two-Way Indicator Species Analysis (TWINSPAN) and Canonical Correspondence Analysis (CCA), Two qualitative (1/0) and eleven quantitative environmental variables were also included in the analyses. All three numerical procedures drew attention to a calcicole-calcifuge distinction as the major pattern in the bryophyte flora. The primary ordination axis from DCA and from CCA ordered the taxa similarly and these orderings were highly correlated with published 'indicator values' of species response to soil reaction. Later ordination axes and divisions in TWINSPAN indicated that moisture requirement, particularly the distinction between the bare Chalk downland and the valley floras on clay and alluvium, the unusual features of the Corallian landscape (presence of rich fens and hard limestones), and the occurrence of the ancient woodland are other major causes of variation in the bryophyte flor a. Rainfall and atmospheric pollution by SO2 were less important explanatory variables, possibly due to confounding with the important geological variables.