BRYOPHYTE AND UNDERSTORY VASCULAR PLANT BETA DIVERSITY IN RELATION TO MOISTURE AND ELEVATION GRADIENTS

Bryophyte and understory vascular plant beta diversities were studied along complex gradients of elevation and moisture in the Canadian Rocky Mountains. Thirty stands were sampled in uniform, stable sites representing a variety of plant community types and widely differing elevational and soil moisture regimes in the alpine, subalpine and montane zones of the Maligne Range in Jasper National Park, Canada. Stands were positioned on a direct ordination of elevation and moisture using altimeter readings and a composite moisture index based on unweighted averages of vascular species moisture index values (1 xeric, 3 mesic, 5 hydric). Stands were then grouped into four elevational and three moisture coenoclines, i.e. stand series, based on their positions in the direct ordination. Beta diversity, i.e. change in species composition along a habitat gradient, was assessed in relation to elevation and soil moisture using several indices. All bryophyte beta diversity calculations were based on the principal substrate found in each stand, to minimize substrate-related effects upon the analysis. Beta diversities of bryophytes and understory vascular plants were similar along moisture gradients in the three vegetation zones, but significantly higher in vascular plants along elevational gradients in the four moisture regimes tested. The highest beta diversities of both plant groups occurred in the moisture coenoclines of the montane zone. It is suggested that bryophytes have wider tolerances to elevation-correlated factors, including temperature, than vascular plants, and consequently broader habitat responses and lower beta diversity along elevation gradients. In a complementary paper (Lee & La Roi 1979) we describe the response patterns of individual byrophyte species to complex gradients of elevation and moisture in Jasper National Park. © 1979 Dr. W. Junk b.v.