Floodplain Succession Pattern in Khorsor Region of Budhi Rapti River, Barandabhar Corridor, Chitwan, Nepal

Abstract

Riverine floodplain forms ecosystem that has great significance in ecosystem services. But frequent change in river course disturbed this floodplain. Budhi-Rapti River formed quite stable floodplain ecosystem nearby Khorsor zone (Barandabhar corridor). As such understanding the process of ecosystem development in the Budhi Rapti river floodplain holds great significance. This study was designed to understand plant colonizing pattern, variation in species richness and composition at the floodplain along the distance based gradient from river bank to the mature forest. Plot size of 20 × 20 m (subdivided into 4 subplots) were established along the two transect (200m apart from each other). First plot was set 200m away from the bank of river and each plot were 50 m apart. A total of 20 plots were sampled along one transect thereby altogether 40 plots were sampled. All vascular plants occurred inside each plot was recorded (0 or 1). The species richness and composition was calculated. Richness for each plant life form i.e. herbs, shrubs and trees were also calculated. Altogether 158 plants (60 families and 136 genera) were recorded; Gramineae being richest followed by Leguminosae, Asteraceae and Cyperaceae. Succession was considered as main variable and measured indirectly through the first axis sample score value after indirect ordination i.e. NMDS. NMDS1 and NMDS2 scores were regressed against species richness as well as species composition variables. Here, total species richness was negatively correlated with the NMDS1 (temporal gradient) which showed convergent pattern of succession. However, herbs and shrubs species richness pattern were negatively correlated with NMDS1 but positive correlation was found with trees and climbers species richness. RDA analysis showed that herbs like Anisomeles indica and Cynodon dactylon as an early successional species and tree species like Ficus hispida and Bauhinia purpurea as late successional species. This study suggests that flood plain succession is convergent type.