Pattern of Tree Species Richness along the Elevation Gradient of Modi River Basin in Annapurna Conservation Area, Central Nepal

Abstract

Elevational diversity gradient is an ecological pattern where biodiversity changes with elevation. Main aim of this study was to find the relationship between species richness along the elevational gradients in southern aspect of Modi River basin Annapurna Conservation Area, Central Nepal. The study was carried out in three elevational zones namely lower (1000-1800m), middle (2000-2800m) and upper elevation (30003800m). Starting from 1000m at Birethanti and ending to 3800m at Machhapuchhare

Base camp at an interval of 200 m. Two transects having 25m × 2.5m sizes were laid

at each elevation band. R- Software, SPSS- Software and Microsoft Excel were used

to perform the statistical analysis. All together 30 tree species belonging to 27 genera

and 21 families have been documented. Among the 21 families Fabaceae was found

to

be the largest family having highest number of genera and species followed by Betulaceae and Anacardiaceae. Species richness of tree species showed bimodal pattern of distribution with elevational gradients. The tree species richness significantly differs along the elevational gradients within different sites. Tree species like Alnus nepalensis, Bombax ceiba were dominant in lower elevational zone; Rhododendron arboreum, Alnus nepalensis were dominant in middle and Betula utilis, Rhododendron arboreum were observed dominant in upper elevational sites. The size class distribution diagram of overall tree species showed reverse J shaped pattern indicating a good regenerating capability of the forest. The regeneration of Alnus nepalensis, Rhododendron arboreum and Betula utilis were higher in comparison to other tree species which was indicated by the higher density of 0-20 size classes of them. The Canonical Correspondence Analysis (CCA) diagram shows elevational gradient strongly affected the study area sites vegetation.