Forest microclimate as a driver of epiphytic bryophyte diversity along a subtropical elevational gradient

Aim: Considering the importance of microclimate in maintaining
the diversity of epiphytic bryophytes, we
investigated epiphytic bryophytes along an elevational gradient
in the subtropical forest of eastern China to unravel the
diversity patterns of epiphytic liverworts and mosses along the
elevational gradients, and the roles of forest microclimates, topographic
variables and host plant composition attributes in shaping these
elevational diversity patterns.  Location: Tianmushan National
Nature Reserve, Zhejiang, China. Taxon: Epiphytic bryophytes.
Methods: Species diversity patterns of liverworts and
mosses were compared based on inventory of 16 plots along an elevational
gradient from 367 m to 1470 m. In-situ microclimatic data of air
temperature and moisture were collected under constant monitoring
for over three years. Spatial linear model and structural equation models
were used to assess the relative roles of the environmental variables in
shaping the patterns of species diversity along elevation. Results: We
found that epiphytic liverwort and moss richness showed different
elevational patterns; overall richness patterns of epiphytic
bryophytes were largely driven by mosses. Epiphytic mosses exhibited a
decline followed by a hump-shaped pattern of species richness with
increasing elevation, while epiphytic liverworts showed a
mid-elevation plateau with a richness maximum between 800
and 1300 m. Forest microclimate, topography and
host plant composition attributes influence epiphytic moss and liverwort
patterns differently and interact in a complex way. Overall, species
richness of epiphytic liverworts was most strongly
affected by microclimate (mean annual air temperature of growing
season) and of epiphytic mosses richness by
topography (Slope). Further, epiphytic liverwort species
richness was more influenced by temperature than moisture. 
Main conclusions: This study highlights the importance
of collecting climatic factors at a fine scale (microhabitats)
for understanding the patterns and drivers of bryophyte
diversity. Further, our findings demonstrate the differences
between liverworts and mosses in terms of their response to different
environments in the forest ecosystem.