A multivariate study of moss distributions in relation to environment in the Gulf of St. Lawrence region, Canada

Abstract

Moss distribution patterns in the Gulf of St. Lawrence were investigated using multivariate analyses to determine the relationship of the patterns to environmental factors. Distance-based redundancy analysis was used to ordinate 29 operational geographical units (OGU) or sampling units based on their moss floras, and hierarchical cluster analysis in combination with indicator analysis was used to produce classifications of both species and sampling units. Climatic variables, in particular, warmth of the growing season, were the most important factors determining species distribution; this resulted in a north–south gradient through the study area. Oceanity was also shown to be important and manifested as an east–west gradient. Edaphic factors, in particular, amount of calcareous rock outcrop, had a secondary influence and modified the patterns established by climate. Ordination of OGUs showed the effects of environment to be more variable in the northern half of the Gulf of St. Lawrence, which may in part explain the higher species richness there. Seven OGU groups were recognized based on cluster analysis of floristic composition. Although indicator species were few, most groups were distinguished by unique sets of regionally rare species. Eleven species elements were identified based on species occurrence in OGUs. The elements constituted sets of overlapping distributions showing southern, northern, and eastern biases in the Gulf region. Multivariate analysis was shown to be effective tool for extracting moss–environment patterns, even at medium geographic scale.Key words: Gulf of St. Lawrence, mosses, environment, richness, distribution, ordination, cluster analysis.