HALL, CHRISTINA C.* AND JEFFREY C. NEKOLA. Department of Natural and Applied Sciences, University of Wisconsin- Green Bay, Wisconsin 54311. - Influence of scale-dependent environmental factors on the distribution of cliff moss species.
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