Bryophyte community composition in a second-order tropical stream at the Luquillo Experimental Forest, Puerto Rico

Streams are important ecosystems that harbor a high diversity of plant species including bryophytes. Studies suggest streams can function as refugia and/or corridors that buffer against the effects of disturbances. In this study, we sampled five sites along a second-order tropical stream in the Luquillo Experimental Forest. We described the riparian bryophyte community composition in conjunction with the physical structure of the stream to understand what environmental factors influence bryophyte composition in the stream. We identified 56 bryophytes, 33 liverworts and 23 mosses; and we recorded cyanobacteria associated with over half of the species of bryophytes. Rocks were the most frequent and important substrate which supported the highest bryophyte richness. Community composition and species diversity were similar among sites. Ceratolejeunea cornuta (Lindenb.) Steph. and Taxithelium planum (Brid.) Mitt. were the most frequent species, recorded in all sites. Although stream width varied between sites, all the other environmental variables measured (canopy cover, temperature, humidity, and elevation) were similar. Across plots, species richness increased with bryophyte cover, whereas canopy cover, location in the stream, substrate, site, temperature, and relative humidity showed no clear associations with richness. Bryophyte community composition seems to be shaped by the substrates occupied. We found that similar types of substrates such as branches, trunks, logs and vines, shared more species in common. This is one of the first studies to describe the bryophyte community of a tropical stream and can provide a baseline for future research on the response of bryophytes to increased disturbances and a changing climate.