The peatlands sampled in this study are located in northern Minnesota and include 32 stands positioned in seven sites in the Red Lake peatland and Lake Itasca areas. Surface water chemistry ranges from pH values of 4.6 to 7.4, with corrected conductivity of 53 to 476 μohms cm−1 and calcium of 6.9 to 44.5 ppm. Six broad physiognomic landscape units are delimited based on quantitative analysis of the vegetation; these range from ombrotrophic ovoid islands to strongly minerotrophic forested fens. These landscape units can best be further divided or themselves characterized by the dominant Sphagnum species. Calculations of niche breadth across eight microhabitat axes and niche overlap for four microhabitat axes (pH, corrected conductivity, height above H2O level, and shade) for 13 species of Sphagnum suggest independent species utilization of the gradients. Among the mire-expanse species, niche breadths become narrower from hollow to hummock along calcium and pH gradients, whereas broadest niche breadths are present for midhummock species along the height gradient. For the taxonomically close species, S. fallax and S. angustifolium, niche overlap is greatest for conductivity and pH, whereas overlap is least along the height gradient. Quantification of niche breadth and niche overlap indicates considerable niche diversification along these microhabitat gradients, with individual species interacting independently to different gradients. These differing niche breadths along several different gradients suggest that these species of Sphagnum are largely equilibrium species, not opportunistic ones. In general, niche overlap is smaller in mire habitats where an abundance of bryophytes coexist with Sphagnum and highest in mire-expanse situations where Sphagnum is dominant.

Eight Sphagnum -dominated kettle-hole bogs in northern Michigan were analyzed to elucidate vegetation patterns of both vascular plants and Sphagnum species in relation to measured bog gradients. Methods of both direct and indirect gradient analysis, including ordination and cluster analysis, were used. Community types as delineated in the ordination are discussed, including species distribution for Sphagnum and vascular plants. Segregation of community types followed gradients of pH, light, and calcium and magnesium ion concentrations. Two types of kettle-hole bogs were distinguished surrounding acid and alkaline bog lakes respectively, each with its own continuum of community types.

The vascular plant and bryophyte vegetation of 50 stands in nine sites from the foothills of western Alberta were quantitatively sampled in order to determine the major vegetation gradients. These fens are mostly patterned, with pools of water (flarks), alternating with raised ridges (strings), and are minerotrophically rich. Mean calcium ion concentrations of the nine fens range between 18 and 37 ppm and mean pH values range between 6.8 and 7.9, with electrical conductivities varying from 140 to 456 μmho/cm (1 mho = 1S). One string community type, dominated by Tomenthypnum nitens, Betula glandulifera, and Larix laricina. and one flark community type, dominated by Scorpidium scorpioides, Drepanocladus revolvens, and Carex limosa, are described, with three phases recognized in the flarks. (The Scorpidium scorpioides phase is most prominent in the wettest flarks, with the Campylium stellatum – Scirpus spp. phase found in slightly drier habitats.) The water chemistry and vegetation of these rich fens compares well with similar mires described from eastern Canada and Fennoscandia. Indirect and direct gradient analysis techniques illustrate a wet–dry ecological series of bryophytes rich in Amblystegiaceae and lacking in Sphagnaceae.

Classical niche theory, particularly in terms of competitive exclusion, does not appear to apply as well to bryophytes as to other organisms. Bryophyte communities, as well as those of other plants and of animals, can be thought of in terms of individual species each utilizing particular portions of various resource or habitat continua. Quantitative studies carried out since 1981, particularly those involving niche breadth and overlap, are reviewed. Special attention is given to niche diversification in Sphagnum, Splachnaceae, bryophyte communities in streams, and to ephemeral bryophyte communities. Some bryophyte communities appear to have equilibrium characteristics and to contain species with relatively narrow niche breadths and with no or only partial niche overlap. In many habitats, however, bryophyte communites have non‐equilibrium characteristics and diversification of species in microhabitats is opportunistic. Do any bryophyte communities persist long enough for complete saturation by species which have realized niches determined by competitive interactions? Recent studies indicate that this is the case for at least some Sphagnum communities, but that it is the exception not the rule for bryophytes.

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