Elevational patterns in tropical bryophyte diversity differ among substrates: a case study on Baru volcano, Panama

Questions. Bryophytes attain their highest diversity in tropical mountain forests. Although distribution patterns have been described, little emphasis has been placed on comparing patterns among substrates (e.g., terrestrial, epiphytic). Understanding these patterns is important, because they determine not only the pool of genetic resources, but also the functioning of these forest ecosystems. Therefore, we studied how bryophyte species diversity changes with elevation, how elevational patterns differ between substrate types, and how elevational trends relate to environmental drivers. Location. Baru Volcano, Panama. Methods. At each of eight elevations, between 1900 and 3300 m, bryophytes were collected in 600-cm2 plots from six substrate types with four replicates. Species cover was registered as a measure of relative abundance. Species richness and community structure were determined and related to elevation, substrate types, and environmental drivers at three scales (plots, sets of four replicate plots per substrate per elevation, and all plots at each elevation). Results. Bryophyte species richness decreased towards higher elevations, at all three scales and on all substrates except bryophytes on soil, for which, at the plot scale, richness peaked at higher elevations than on the other substrates. Relative humidity explained richness slightly better than elevation. Communities at the lowest elevations had the most uneven compositions, due to the presence of many small species with low abundance. Conclusions. In studies on the spatial distribution of bryophyte diversity, it is essential to consider different substrates and spatial scales separately. If substrates differ in their elevational species-richness patterns, climate and land-use change may affect bryophyte diversity patterns not only directly, but also indirectly via changes in substrate availability. Therefore, a better understanding of the spatial variation in bryophyte diversity in mountains is essential to elucidate the effects of environmental change on this important group of plants and their implications for ecosystem functioning. FILE: Main data base_JVC.xlsx Sheet=TaxonomicInformation Our database contains taxonomic information on bryophyte species collected along an elevation gradient on the Baru volcano, Panama. Sheet=data The relative abundance of each species or morpho-species is included per 600-cm2 plot in each of the six considered substrates (soil = terricolous, rock = saxicolo