The Forest Ecotone Effect on Species Richness in an Arid Trans-Himalayan Landscape of Nepal

Abstract

Changes in species composition and richness across the sub-alpine forest ecotone are well known phenomena. The total number of species at a regional scale drops substantially above the forest-line in the central Himalayas of Nepal. This study tests the effect of a forest border ecotone on a local scale using a grain size of 100 m 2 . We sampled a set of vertical transects across a sloping sub-alpine forest line where canopy and temperature covary, and a set of horizontal transects across a forest ecotone where there was no altitudinal difference to eliminate the influence of temperature. Detrended correspondence analysis revealed a continuous change in species composition across the forest border ecotone. Species turnover was, in general, low, and species richness did not vary very much between the forest and open landscapes. We attribute this to the grazing and browsing pressure in the area, which may have lowered the tree line. A reduced tree line compared to the climatic limit may facilitate enhanced species richness above the forest line. There was no significant difference in species richness between forest and open landscapes along horizontal transects where temperature variations were minimized. This study exemplifies the difficulties encountered on a local scale when one aims to test diversity hypotheses deduced from general models on forest-ecotone effect and mass effect. The low species turnover and minor differences in alpha diversity may be because the area is a cultural landscape and the homogenizing effect of domestic animals overrides some of the edge effects of the ecotone.

A trait‐based approach reveals the importance of biotic filter for elevational herb richness pattern

“…The effect of OC on herb richness has also been supported by other studies (Camarero, Gutiérrez, & Fortin, ; Hodačová & Prach, ), suggesting that OC could act as a biotic filter that structures herb communities. In contrast, when Jiang, Ma, Anand, and Zhang () and Shrestha and Vetaas () applied a similar method (based on vertical and horizontal transects), they did not find a negative relationship between OC and herb richness. This disparity might be explained by different environmental conditions; for example, OC may facilitate herb richness in an arid system via increased understorey humidity in summer (Ramírez, Rey, Alcántara, & Sánchez‐Lafuente, ), and therefore, the influence of OC on herb richness might be conditional on multiple limiting factors.…”

Effect of anthropogenic disturbance on plant species diversity in oak forests in Nepal, Central Himalaya

“…In paper III, I refer to this border zone as a 'forest ecotone' or 'forest line ecotone'. In this study, the forest patch of 0.1 ha with > 50 % canopy cover was considered as forest (Shrestha & Vetaas 2009). Approximate elevational positions from the study area at Ngawal (dry area) are shown for the different eco-regions across the treeline ecotone.…”

Plant species and communities assessment in interaction with edaphic and topographic factors; an ecological study of the mount Eelum District Swat, Pakistan

“…The plant communities highlight changes in response to various factors not only related to its zone of origin but also to its ecology ( Afzal et al, 2000 ). The most simply interpretable sign of biological variation is species richness which highlight by different environmental characters ( Khan et al, 2016b , Shrestha and Vetaas, 2009 ). Researchers study several factors (abiotic and biotic) basically which interact in community structure formation.…”