Fern species richness and diversity in the forest ecosystems of Papua New Guinea. A case study along an elevational gradient

This study aims to analyze the occurrence and composition of ferns along an elevational gradient and among different forest types and disturbance regimes in Papua New Guinea (PNG). The assessment was conducted using the monitoring protocol of the National Forest Inventory. The investigation revealed a high richness of ferns, with 122 species or morphospecies from 51 genera and 21 families. Among them, 81 species were terrestrial and 16 were epiphytes. The project also highlighted increasing richness with elevation, both for terrestrial and epiphytic ferns. Reflecting other environmental variables, elevation was a significant proxy factor in determining the taxonomic composition. Lowland forest was clearly differentiated from the montane one, which was characterized by epiphytic species from the Drynaria and Ctenopteris genera. Lowland disturbed and primary forests were slightly differentiated in terms of fern composition, the latter characterized by sciophilous species belonging to the Polypodium, Microlepia, and Pronephrium genera and the former mainly by species of the Gleichenia genus adapted to forest margins and gaps. The research points to the richness of ferns in PNG and their effectiveness as a potential indicator to characterize and monitor forest types and their conservation status with respect to a disturbance regime. In the future, studies should aim to increase species sampling in abundance and seek precision in understanding species response variables in diverse forest regimes.