Plant species diversity and density patterns along altitude gradient covering high-altitude alpine regions of west Himalaya, India

Understanding species richness and diversity patterns and their governing factors in less-to-unexplored regions across Himalaya provide invaluable insights into exploring drivers which shape as well as influence plant community structures. The present investigation explores plant species richness and diversity patterns across different growth forms and its association with environmental parameters along altitudinal gradient (3200 m-4800 m) in alpine regions of west Himalaya, India. A total of 265 plant taxa were documented from study area with higher proportion of herbs (212), followed by shrubs (44) and trees (9). Species richness, diversity, and density patterns were estimated for each growth form along altitude gradients using polynomial regression and an apparent monotonically decreasing trend (p < 0.05) was seen across transects, with highest values for herbs. Beta diversity, estimated for each transect, was low in Darma for herbs exhibiting high species packaging and homogenous composition, and high in Mana showing more scope for occurrence of rare/occasional herbs. Four major distinct altitudinal zones were identified for Uttarakhand alpines using cluster dendrogram, i.e., 3200 to 3500 m, 3600 to 3900 m, 4000 to 4500 m and 4600 to 4800 m with respect to their vegetation composition. NMDS of combined dataset along altitude gradient across transects also exhibited proximity among lower altitudesof transects with similar species composition (like Anaphalis, Danthonia, Geranium, Pedicularis, Potentilla), while high-altitude plots were scattered towards both ends of axesinhabiting specialized plant species (like Gentiana, Nardostachys, Saussurea, Sedum, Swertia). The relationship between vegetation variables (richness, diversity and density) and climate variables was modelled using Pearson’s correlation (P < 0.001) and temperature, precipitation, and solar radiation exhibited positive correlation, while windspeed showed negative correlation. Relative effect of climatic parameters on species composition, analysed by CCA, showed strongest influence of precipitation in vegetation zones with high axes correlation, followed by temperature, isothermality and wind speed, while influence solar radiation was lowest. Thus, under the current climate change scenario, any change in these factors may alter the composition of these high-altitude area and threaten the unique flora as well as the fauna dependent on it. Hence, any effort made towards conservation would eventually benefit a significant proportion of Himalayan biodiversity.