Moss communities of xeric calcareous habitats in the southeastern United States: An assessment of compositional variation and distance decay

Abstract

Moss floras of xeric calcareous habitats were studied at field sites in Florida, Alabama, Georgia, Tennessee and Kentucky. At each site, one study area was established, including open glade and wooded margin. A species inventory and a community composition investigation were conducted at each study area. Community composition was analyzed for ground-dwelling (soil and rock) and corticolous communities. Ground-dwelling communities were sampled with quadrats, and corticolous communities were sampled by examining trees along the margins. Presence/absence data from the complete species lists from the five sites were used to calculate Jaccard similarity indices among pairs of sites. The frequencies of species occurring in community samples were used to calculate Bray-Curtis similarity indices for ground-dwelling margin and corticolous communities. Jaccard and Bray-Curtis similarities were used in regression analyses to explore their relationship with geographic distance and climatic factors. The total number of species found at each 1 ha study area ranged from 32 to 35. Part of the flora at each site consisted of species common elsewhere in the region, but there were also species commonly associated with calcareous substrates, such as Pleurochaete luteola, Weissia jamaicensis, Orthotrichum strangulatum, Schistidium rivulare and Hyophila involuta. Regression analyses of pairwise similarities and geographic distances showed a strong non-linear correlation between distance and the Jaccard similarities, a somewhat lower correlation between distance and the Bray-Curtis similarities from ground-dwelling margin communities, and little correlation between distance and corticolous community compositions. Multiple regression analyses suggested significant correlations between community variation and temperature and in most cases weaker correlations with precipitation. Our results were notable in that the ground-dwelling community subset exhibited a pronounced distance decay but the corticolous subset did not. This finding suggests that in bryophytes characteristics associated with habitat fragmentation and substrate type have important effects on beta diversity.