Bryophyte distribution and environment across an oceanic temperate landscape

Correlations between environmental variables and species distributions can make an important contribution to the formulation of hypotheses of cause-and-effect relationships. At a resolution of 2 x 2 km, presence/absence data for bryophytes have been collected recently for an area of 4553 km 2 in north-west England. The aim of the present paper is to make use of these data in order to investigate the relationship between bryophyte distributions and environment at the landscape level. Analysing the north and south of the study area separately, the major distributional variation of bryophytes was identified using Detrended Correspondence Analysis (DCA) and a comprehensive set of environmental variables was fitted onto the ordination spaces of the first two DCA axes. Altitude (an indirect environmental variable) was most strongly associated with changes in bryophyte distributions in both the north and south, and was coupled with important changes in habitats. Direct and resource variables associated with the altitudinal gradient seem in particular to be related to water supply, nutrient limitation and substrate pH. Alkalinity of the solid geology has an important secondary influence in the north where large exposures of limestone exist, but the scarcity of this rock on the surface of the south results in no major influence on bryophyte distributions. Results are discussed in relation to other comparable studies, which show some clear similarities with the present outcomes, and the major direct and resource gradients that appear to be present at large scales.