Vascular Plant Species Richness along Elevation Gradient ofthe Karnali River Valley, Humla District, Nepal Himalaya

Abstract

The Himalayan mountain range exhibits the largest elevation gradient in the world and a very wide range of climatic zone.Study of species richness with elevation has been known for over a century and found a different trend with elevation. This study shows the pattern of species richness with altitude and the environmental factors that are responsible for creating such pattern. The study was conducted in Humla District, North-West Nepal which is located near recently declared Api-Nampa Conservation Area.The sampling method was designed to include all the habitat types and vegetation zones within 2800 to4400 m in the southern slope of the southern Himalayan main range. Five plots of 10 ×10 m were sampled in each 100 m elevation band i.e. a total of 80 plots between 2800-4400 m. Presence–absence data was used for the analysis. Latitude, longitude,altitude,aspect,soil pH,soil moisture, rock cover and grazing intensity were recorded for each plot. The total vascular plants along with the life forms were regressed against the altitude as well as different environmental parameters.A Generalised Linear Model was used to elucidate the pattern of species richness. A Poisson error distribution with a Chisquare-test statistics was usedfor the analysis. A quasi-Poison error distribution with F-test was used where the data showed the over dispersion.A total of 199 vascular plant species were recorded of which 165 species were dicots, 23 monocots, 145 herbs,21trees, 35 shrubs, 7 gymnosperms and 4 pteridophytes. Species density of total vascular plants and all life forms showed a unimodal pattern except monocot (linear pattern) with altitude. Species density of total vascular plants showed a linear pattern with RRI, pH, rockcover and grazing intensity however,a unimodal pattern was observed with soilmoi sture. Species richness of total vascular plants and all the life forms showed aunimodal pattern with altitude.The species richness pattern was found similar for both empirical and interpolation of species data . Besides that the species richness pattern was also similar for different life forms. A number of environmental variables play a dominant role to explain the pattern of richness at the local scale.Thus, considering multiple gradients would help to reveal better pictures of richness patterns and the potential mechanisms that structure the distributions of biodiversity in high mountainous region.