Niche Relationships of Mountain Stream Bryophytes Author(s):

Bryophyte community structure was studied in ten streams in the Adirondack Mountains of New York and adjacent areas over an elevation range of 625 m. Species composition, including frequency and cover and possible niche parameters including elevation, water temperature, pH, flow rate, incident light, substrate type and height above or depth below water level were measured. An ordination was done of the ten streams, and species diversity, niche breadth and niche overlap were calculated. Elevation and stream flow were important for niche separation between streams. Height and type of substrate including rock size were important niche parameters within streams. Characteristic height segregation was seen within streams formany species including several co-occurring members of the Brachytheciaceae and two morphologicalforms ofHygrophypnum ochraceum. The communities included 28 mosses, seven hepatics and one aquatic lichen. It is advantageous to be able to test interactions within a group ofbryophytes in a habitat dominated by bryophytes. Many habitats fill this requirement, but few have been studied in terms of community structure. Forest floor communities (Slack 1977; Lee & LaRoi 1979a, 1979b) and bogs and fens (e.g., Slack et al. 1980; Vitt & Slack 1984) have been analyzed. Although both forest floors and mires are often dominated by bryophytes in the ground layer, these habitats are complicated by the large number of non-bryophyte plant species also present. Mountain streams, the subject of the present study, are often virtually free of higher plants. This absence of multilayer plant association facilitates the study of bryophyte species interactions. Early studies of North American stream ecosystems emphasized the importance of allochthonous detritus as the major energy source. Naimer, in the 1982 meetings of the North American Benthological Society, was the first to report that bryophytes are important biological contributors to these systems since they constitute a major part of the primary productivity in lower order streams. Bryophytes are also important as a substrate for insects 007-2745/85/7-18$1.35/