Effect of Transhumance in Species Richness and Composition in a High-Altitude Landscape, Langtang National Park, Nepal.

Abstract

Transhumance in the Himalayas is accompanied by vertical movement of the livestock in a cyclic manner. There is a perception that, due to this activity, highland pastures are overgrazed which is associated with increasing bush cover and it has resulted decrease in biodiversity. With the main objective of exploring effect of transhumance in biodiversity in subalpine and alpine pastures in Langtang National Park, Nepal, the study addressed the following questions (i) is grazing related to change in species richness and composition along a grazing gradient [distance from goth (semi-permanent hut used during seasonal vertical migration of livestock in the Himalaya) to surrounding has been considered in this study to represent a grazing gradient]?; (ii) does grazing and its effect vary with different habitat patches? (iii) how does the effect of habitat type and distance from goth on species richness and composition vary with altitude? Data set consist of 17 environmental variables and 101 species recorded from 180 4-m2 plots (60 plots from each grass-, shrub- and stone-dominated patches) from 6 goths in three altitudes (low, mid and high; 2 goths in each altitude). Dung, trampling and bare soil showed high grazing pressure in grass-dominated patch than in other habitat patches and it decreased with increase in distance from goth. But species richness was lowest in grass-dominated patch and highest in shrub-dominated patch. There was an increase in species richness with the increase in distance from goth in grass-dominated patch reflecting decline in species richness within 70 m distance from goth. Canonical Correspondence Analysis (CCA) with forward selection of environmental variables in whole dataset in CANOCO showed that 12 out of 17 studied environmental variables had significant effect in species composition, being altitude, shrub and grazing more important than others. Nitrophilous and disturbance tolerance species showed affinity toward increasing level of trampling and dung in the CCA diagram. Distance from goth showed strong effect in species composition in grass-dominated patch and mid altitude site than in low and high altitude sites. The study concluded that grass-dominated patches were associated with high grazing intensities and low species richness than in shrub-dominated and stone-dominated patches at the local level. Grazing gradient was clearly evedient in such heavily grazed patches and grazing had more pronounced effect in mid altitude pastures at the landscape level. Key words: Canonical Correspondence Analysis (CCA), General Linear Model (GLM), goth, grazing, ordination, pasture