Floral Species Richness Pattern in Arghakhanchi and Adjoining Areas, Nepal

Abstract

The biodiversity and their pattern may vary from a broad geographic area to a small local scale due to changes in their linked components along spatial and temporal gradients. Basic knowledge of distribution, diversity, and roles is necessary for the conservation of any group of organisms. In this synthesis I examined the variations in species composition and richness patterns over various spatial gradients and how they relate to the nutrients found in the low mountainous regions of west Nepal.

This thesis is based on field-survey data of vascular and lichen species, analyzed soil data as well as secondary data from published articles. The study is mainly focused on vascular plant as well as lichen species composition, richness and soil heterogeneity, which is based on direct field sampling in national and community forest of Arghakhanchi and adjoining area: Resunga forest of Gulmi district, Nepal, to compile baseline information. The survey was done in autumn and spring seasons for two consecutive years (2018-2019) at various elevations that varied from 200 to 2300 m. The primary data of vascular plants was collected by use of 10 X 10 m quadrats in stratified random sampling design along the elevational gradient. From the same sampled plots, lichen specimens and soil samples were also collected. The soil samples were chemically analyzed in laboratory. The vascular and lichen specimens were identified by comparing with already identified herbarium specimens and by following identification keys. The data was analyzed by use of various statistical techniques: Generalized linear model (GLM) regression, PerManova, DCA and CCA ordinations in R software. The elevational diversity indices (Shannon-Wiener, Simpson and Pielou’s evenness) of plant life forms were estimated.

A total of 606 species of vascular plants and 47 species of lichens were found in the field. Plant life forms classified by Raunkiaer (1934) yielded the following results: 265, 37, 158, 57, and 89 species for Phanerophytes, Chamaephytes, Hemicryptophytes, Geophytes, and Therophytes, respectively. According to the different types of forests, the mixed pine forest containing Schima wallichii, Castanopsis indica, Pinus roxburghii obtained the highest vascular species richness. Capillipedium assimile is the species which obtained bear the highest Important Value Index in all three ecological regions (Tropical, Sub-tropical and Temperate). The regression results show that all vascular plants, life-forms species and lichen species follow the statistically significant elevation-dependent unimodal structure. Unimodal pattern is found as common elevational species richness pattern, but is not compulsory pattern against elevation in small areas.

The explanatory factors show a stronger influence on species composition than species richness, according to correlations and canonical correlations. The Hemicryptophytes, Phanerophytes and Therophytes had significant positive relationships with elevation and soil nitrogen, whereas the Chamaephytes, and Geophytes, had a negative relationship. Elevation and nitrogen function show the uniqueness of the interplay between life forms by acting as key factors of plant dispersal. Other factors-RRI, soil pH, phosphorus, potassium show comparatively less impact in species composition.

According to the appearance of a peak in species diversity at nearly the same elevation and a pattern that is similar, the diversity of vascular plants promotes the abundance of lichens. The diversity of lichens was strongly correlated with the habitat and elevation than the aspect of hills. At all levels of spatio-temporal gradients, species richness and composition patterns are strongly scale dependent. Certain variables, such as soil-related local-scale heterogeneity and slope aspect, are essential for figuring out species composition and richness trends.

Based on our results, it is cleared that the study area: Arghakhanchi district and its adjoining areas provide variable habitats for vascular as well as lichen community. Open ground floor is mainly rich in native as well as alien herb plant species, which are less dominant in forests. It is clear that species composition is a more useful tool in landscape ecology and biogeography research than species richness. Therefore, plant community structure should be used as a reliable and insightful indicator in biogeography studies and conservation planning.