Biodiversity of pteridophytes at Mulawella Mountain of the Sinharaja Forest

Abstract

Pteridophyte flora represent an important component of natural vegetation and about 362 taxa belongs to 30 families have been described in Sri Lanka. Even though Pteridophytes play a significant role in natural ecosystems, they are one of the least studied plant categories in Sri Lanka. Although majority of Pteridophytes (81%) have been distributed in the wet zone of the country, little is known about the diversity of them even at Sinharaja Forest which provides a natural refugee for many species. Therefore, the objective of this study was to initiate a systematic study on Pteridophytes at Sinharaja Forest with respect to species and habitat diversity.

The study was conducted in the Mulawella Mountain. Nine plots of 20×20 m were established randomly along the stream. Each plot was divided to four sub plots. All Pteridophytes growing in each sub plot were identified to species level and their number was recorded. Pteridophyte species observed were categorized according to their life forms. Diameter at breast height of all tree species above 5 cm dbh was measured along with their number. Number of saplings from all tree species was also counted. Point diversity of Pteridophytes was estimated as number of species recorded in each plot of 100 m2 and Shannon-Wiener diversity index was calculated. In addition to plot assessment, all Pteridophytes along the stream and other areas were also identified to species level to prepare the checklist for the area.

The study plots and assessments of stream banks and other specific areas documented 63 species belonging to 20 families. Twenty two percent of recorded Pteridophytes in Mulawella area were endemic to Sri Lanka. A check list of Pteridophytes was prepared for the study area. Two extremely rare species namely, Teratophyllum aculeatum and Lindsaea repens were also recorded from the area. A single specimen was recorded which closely resembles Prosaptia ceylanica which is presently limited to a type specimen only at the Kew Herbarium, UK. However, only 28 species (44%) which belongs to 12 families were identified from a total 0.36 ha of randomly selected sample plots. Terrestrial category was the dominant life form with 49% of species at Mulawella mountain area followed by epiphytic (34%) and lithophytic (16%). Only four species were observed in both epiphyte and lithophyte habitats. Elevation of the study area changed from 515 to 750 m amsl, however, the number of fern species and total number of ferns did not show correlation with increasing elevation. Shannon’s Wiener diversity index for individual plots varied from 0.44-1.89. Cumulative number of species showed significant asymptotic relationship with cumulative area surveyed. Based on the results, requirements for future sampling of Pteridophytes have to be developed.