Habitat Differentiation of Ferns in a Lowland Tropical Rain Forest

Abstract

Fern species and growth form diversity peak in tropical rainforests. In such forests, ferns often play important ecological roles. However the distribution and diversity patterns of different growth forms (i.e., epiphytic vs. terrestrial ferns) have not been broadly quantified. We compared the distribution and diversity patterns of epiphytic pteridophytes on the trunks of six individuals of the emergent canopy tree species Hyeronima alchorneoides (Euphorbiaceae) to those of terrestrial species at La Selva Biological Station in Heredia province, Costa Rica. A total of 21 species of epiphytic and 20 terrestrial ferns was recorded, with only one species found as an epiphyte and as a terrestrial species. Epiphytic species also exhibited increasing species diversity with increasing trunk height. Epiphytic species exhibited predictable patterns of distribution along the trunk and were easily grouped into high-trunk, low trunk, or bimodal categories. In terms of percent cover and number of species, simple-leaved ferns dominated the epiphytic growth form, 13 of 21 species, whereas ferns with compound or dissected leaves dominated the hemi-epiphytic and terrestrial floras with 20 of 20 species. These results indicate that there are significant functional differences in the ecology of epiphytic and terrestrial ferns and that reciprocal establishment is difficult and extremely rare.