Does moisture affect the partitioning of bryophytes between terrestrial and epiphytic substrates within cool temperate rain forests?

Abstract

Bryophyte communities are highly sensitive to moisture and/or humidity levels. Most studies on the subject focus on bryophytes on either tree or ground habitats and do not consider how bryophytes partition themselves across both ground and epiphytic substrates within the same forest. Sampling mesic temperate forest sites of the same physiognomy from two Tasmanian regions with slightly different moisture levels (a wetter northwest versus a drier northeast region), we examine various aspects of the community structure (overall liverwort and moss cover; species richness; and liverwort to moss ratios) of both tree and ground communities with respects to moisture availability. We then test the hypothesis that a wetter site will exhibit a greater magnitude of bryophytes inhabiting both tree and ground habitats. Results of the analyses show that the ground habitat in the northwest sites exhibited a significantly higher mean species richness, higher overall and mean liverwort to moss ratio, and a higher liverwort cover than the northeast sites. This suggests that the northwest had a more ameliorated ground microclimate than the northeast. In terms of habitat partitioning, a significantly higher percentage of taxa occupied both tree and ground habitats in the northwest, compared to the northeast, which exhibited a higher percentage of taxa restricted to trees. It is proposed that within a single vegetation type, a higher site moisture level may create microclimates conducive to more bryophyte species in both tree and ground habitats, especially the latter, thereby enabling taxa to colonize and coexist on both substrates more freely.