Riparian plant species of Sherichhu River in Eastern Bhutan: their diversity, distribution, and ethnobotanical uses

The floristic study along the Sherichhu River was carried out to determine the riparian plant species diversity and distribution pattern. A total of 34 study plots were laid on either side of the riverbank and recorded 72 woody species belonging to 52 families and 61 genera. Based on ocular inspections and topography, the areas were categorised into U-shaped and V-shaped valley. These two valleys, though differing in topography, has fostered the existence of diverse plant species in the study area. A considerable variation in the species diversity and richness was observed between the V-shaped and U-shaped regions based on the Shannon diversity index (P = 0.013) and species richness (P = 0.005) values. The Importance Value Indices (IVI) were highest for Desmodium elegans, Mallotus philippensis, and Rhus paniculata in the V-shaped area and Murraya koenigii Duabanga grandiflora and Quercus glauca had the highest IVI in the U-shaped area. Fabaceae, Euphorbiaceae, Anacardiaceae exhibited a high family value index (FVI) in the V-shaped area, while the U-shaped area had a high FVI for Rutaceaec, Lythraceae, Fagaceae, and Myrtaceae. Structurally, the Mallotus-Desmodium-Rhus community was dominant in the V-shaped area, while Duabanga-Terminalia-Murraya and Quercus-glauca woodland communities were dominant in U-shaped valley. The CCA analysis revealed that the slope and litter thickness had shown greater influence on the plant species composition. In general, topography, micro-habitat conditions, river channel width, and flood regimes may have influenced riparian plant species diversity and distribution patterns. Thus, identifying key plant community types and underlying environmental conditions may help to accomplish and safeguard forest resources in the area. Riparian vegetation along the Sherichhu River is also a habitat for medicinal plants (11 out of 72 woody species), a source of food and income to rural communities. Thus, future studies should also focus on devising appropriate strategies for protecting and conserving Bhutan's riparian ecosystem from global warming.