Species richness patterns along altitudinal gradient in Manaslu Conservation Area, Central Nepal’

Abstract

Species richness is currently the most widely used measure of diversity which is assumed as a simple and easily interpretable indicator of biological diversity. The present study was carried out in Manaslu Conservation Area, namely two VDCs Samagaun and Lho. The study addresses the plant species richness patterns, floristic composition and distribution as well as a comprehensive series of environmental factors affecting the vegetation of the area. A total of 70 plots of 10 m x 10 m each were laid from the altitude of 3000 m to 4400 m in different habitat types with in an interval of 100 m altitudinal band. Five subplots were laid in each altitudinal band. All the flowering plants species present in each plot were documented. Moisture, pH, aspect, latitude, longitude and altitude of each plot were recorded. The flowering plants were further classified into various lifeforms as dicots, monocots, gymnosperm, woody and herbs and their altitudinal range were also computed from Press et al., (2000) for interpolated empirical richness. Detrended Correspondence Analysis (DCA) was used to analyse the distribution and abundance of the species with respect to altitude. A Generalized Linear Model (GLM) along with quasi-Poisson error distribution and F-test statistics was used to evaluate the richness pattern along the altitudinal gradient. The patterns of richness were interpreted with relation to altitude, soil moisture and pH. A total of 161 species were recorded, representing 124 dicots, 24 monocots and 10 gymnosperms. Dicots (124 species) were found dominant over the monocots (24 species). Similarly, herbaceous species (114 species) dominated the woody species (47 species).Total species density varied from 29 to 62 within the sampling plots. A unimodal relationship between diversity pattern and altitude was the most common pattern observed. Species density of dicots, monocots and herbs showed a unimodal pattern when regressed against altitude while woody species and gymnosperms decreased linearly with altitude. The species richness (except woody species, which showed linear decrease) and interpolated empirical richness of all the life forms showed a unimodal pattern with altitude. A positive linear pattern was observed when moisture and pH were regressed against altitude. No significant relationship was found between the species density and RRI. The environmental variables play significant role to explain the species richness patterns. Therefore, these do affect the patterns, composition and distribution of plant species.