Habitat limitations of Sphagnum along climatic, chemical, and physical gradients in mires of western Canada

Sphagnum distribution was studied on twenty-seven peatlands found along a transect extending from the Queen Charlotte Islands, British Columbia, to central Alberta. Based on surface water chemistry, oceanic mires are either ombrotrophic bogs or poor fens, while in subcontinental areas, mires range from extreme-poor fens to moderate-rich fens. Species are grouped into five clusters; stands into ten. Species groups and stand dispersal are determined by climate and surface water chemistry, especially corrected conductivity and calcium, magnesium, and potassium concentrations. Sphagnum species habitats are limited to mires having low cationic contents and corrected conductivities. Seven of eighteen species studied are limited by climatic factors to oceanic areas. Sphagnum fuscum is the most widespread of all the species studied, independent of climate and surface water chemistry. Only three Sphagnum species are present in moderate-rich fens. Most of the species height requirements along the hummock-hollow gradients are present on the mires studied, and the height relative to the water table does not limit the geographic distribution of these species. Height is limiting only for species found at either end of the topographic gradient. Tree-produced shade does not limit the habitat of any of the species studied.