ENVIRONMENTAL RELATIONS OF THE BRYOPHYTIC AND VASCULAR COMPONENTS OF A TALUS SLOPE PLANT COMMUNITY

The environmental factors correlating with community structure of vegetation on talus slopes of the 785 km long Niagara Escarpment, southern Ontario, Canada, were studied using canonical correspondence and regression analysis. The bryophytes and higher vascular plants were analysed separately to see if their responses were similar or different. Both vascular plants and bryophytes responded similarly to the environmental variables that were measured. For both vegetation components, location from north to south explained most of the variance. When species richness was plotted against location for the complete vegetation and for the two components separately, the results showed that vascular plant species richness decreased with increasing latitude, while bryophyte richness increased. The magnitude of both of these trends was slight but consistent with the hypothesis that available environmental energy governs a significant amount of the variance in species richness. Since separate components of the talus vegetation were shown to respond differently to the same environmental variable, groups of taxa should not be excluded from community level studies without a consideration of the possible consequences of this bias.