ECOTOPE DIMENSIONS OF PEATLAND BRYOPHYTE INDICATOR SPECIES ALONG GRADIENTS IN THE MACKENZIE-RIVER BASIN, CANADA

A TWINSPAN analysis based on bryophyte species distribution and abunda nce divided peatlands in the Mackenzie River Basin into seven types. T he analysis also selected seventeen bryophyte indicator species for ea ch division within the classification or for the characterization of t he peatland types. The most important environmental and climatic gradi ents segregating the seven types and the distribution and abundance of indicator species were pH, moss height relative to the surface water table, annual precipitation, and mean annual temperature. Ecotopes of each of the indicator species were analysed using response surfaces in ecological and climatic spaces. The southern limits of most species d istributions roughly coincide with the southern limits of the Mackenzi e River Basin, whereas the ranges of most species extend into more nor therly areas. However, these northern extensions were in habitats othe r than peatlands; habitats that are not examined in this study. Specie s with the widest ecological and climatic ecotopes were such hummock s pecies as Tomenthypnum nitens, Sphagnum fuscum, Polytrichum strictum, Dicranum undulatum, Pleurozium schreberi, Hylocomium splendens, and Au lacomnium palustre. The presence of permafrost has created higher peat surfaces than those found in warmer regions, and provides new habitat s for hummock species. Lawn and hollow species have narrower ecotope d imensions and become infrequent in peatlands at the northern limit of the study area due to loss of suitable habitats in perennially frozen peatlands.