Worldwide, cliffs represent stable ecosystems that have been little disturbed by human activities, and are important reservoirs for regional biodiversity. Community composition patterns at >1 m2 scales in cliff habitats, across a wide range of taxa groups (including bryophytes), demonstrate abrupt changes perpendicular to cliff faces but relatively little variation parallel to them. Significant variation in community structure parallel to cliff faces, however, has been documented at smaller scales (0.01-1 m2; Larson et al. 1999). What is not clear is the level to which scale dependence in environmental variation is responsible for these differing patterns. In this study, the frequency of cliff bryophyte species and habitat variation across three different scales were analyzed to determine how environmental at various scales affects moss distribution. Four sites were investigated along a 100 km section of the Niagaran Escarpment in northeastern Wisconsin. At each site, transects were laid out at 4 m intervals in bryophyte rich areas from outcrop top to bottom (maximum height = 3 m). 1-2 areas were sampled per site, with 5-12 transects within each. Along each transect, 10x10 cm quadrats were placed sequentially along the entire length. Moss species and microhabitat (face, ledge, overhang, horizontal cracks, vertical cracks, and pits) frequency was recorded from each quadrat. These data were analyzed to determine the relative importance of micro- (microhabitats within quadrats), meso- (outcrop aspect and exposure), and macro-scale (bedrock chemistry, site isolation, and history) environmental factors in predicting the abundance of individual cliff moss species.

Key words: bryophytes, cliff, niche space, scale dependence