Assessment of diversity and distribution patterns of Pteridophytes in the South-Central Biological Corridor III of Bhutan

Pteridophytes constitute an important component of forest ecosystems in addition to non-vascular cryptogams and spermatophytes (Magnoliophyta). Study has been carried out to assess the diversity and distribution patterns of pteridophytes in Biological Corridor III of South Central Bhutan with an aim to evaluate species composition along elevation-gradients and to understand how environmental factors influence species richness and distribution. Line-transect methods were adopted on site in four different locations. Species richness and diversity study was conducted in 47 sample plots taken at sizes of (10 x 10m) at 500m interval from 800 to 2200m altitude in three forest types. A total of 64 fern species were recorded represented by 3146 individual plants. Maximum species richness was observed at elevations between 1000 and 2000m. The species diversity index was (H = 1.368), evenness (EH = 0.88) and species richness (SR = 5.1). Pteris normalis was found to have the highest relative abundance of (RA = 9.91); Selaginella monospora had the highest relative density with (Rd = 11.35) and the maximum Importance Value Index of (IVI = 26.48) distributed along the widest range of elevation. Environmental and ecological variables such as temperature, slope and soil pH tend to have negative correlation with species counts. Elevation, soil-moisture content, precipitation and canopy coverage tend to have a positive correlation. Species counts through different vegetation zones tend to increase from tropical to subtropical and gradually decrease towards warm temperate forest.