Global average temperature increase during the last century has induced species geographic range shifts and extinctions. Montane floras, in particular, are highly sensitive to climate change and mountains serve as suitable observation sites for tracing climate-induced biological response. The Himalaya constitute an important global biodiversity hotspot, yet studies on species’ response to climate change from this region are lacking. Here we use historical (1849–50) and the recent (2007–2010) data on temperature and endemic species’ elevational ranges to perform a correlative study in the two alpine valleys of Sikkim. We show that the ongoing warming in the alpine Sikkim Himalaya has transformed the plant assemblages. This study lends support to the hypothesis that changing climate is causing species distribution changes. We provide first evidence of warmer winters in the region compared to the last two centuries, with mean temperatures of the warmest and the coldest months may have increased by 0.76±0.25°C and 3.65±2°C, respectively. Warming-driven geographical range shifts were recorded in 87% of 124 endemic plant species studied in the region; upper range extensions of species have resulted in increased species richness in the upper alpine zone, compared to the 19^th century. We recorded a shift of 23–998 m in species’ upper elevation limit and a mean upward displacement rate of 27.53±22.04 m/decade in the present study. We infer that the present-day plant assemblages and community structure in the Himalaya is substantially different from the last century and is, therefore, in a state of flux under the impact of warming. The continued trend of warming is likely to result in ongoing elevational range contractions and eventually, species extinctions, particularly at mountaintops.

That the Himalaya contain the basins of major rivers, regulate regional climate, and harbor rich biodiversity and varied ecosystems is well known. The perennial waters and biodiversity are closely linked to the livelihoods of over a billion people. The Himalaya are stressed because of a burgeoning human population and the escalating pressures of deforestation; urbanization; hunting; overexploitation of forests; and, more recently, intensive dam building. The cumulative effects of these forces have led to biotic extinctions and an increased frequency of hazards threatening human lives, livelihoods, and property. However, there is largely no comprehensive account of these challenges facing the Himalaya. We review and discuss the importance of the Himalaya and the need for their conservation by exploring four broad themes: (1) geobiological history, (2) present-day biodiversity, (3) why the Himalaya are worth protecting, and (4) drivers of the Himalayan change. We suggest scientific policy interventions, a strengthening of institutions, and proactive institutional networking to reverse the trend.

The Himalaya is one of the youngest and the loftiest mountain chains of the world; it is also referred to as the water tower of Asia. The Himalayan region harbors nearly 10,000 plant species constituting approximately 2.5% of the global angiosperm diversity of which over 4,000 are endemics. The present-day Himalayan flora consists of an admixture of immigrant taxa and diversified species over the last 40 million years. The interesting questions about the Himalayan flora discussed here are: how did the Himalaya achieve high endemic plant diversity starting with immigrant taxa and what were the main drivers of this diversity? This contribution aims to answer these questions and raise some more. We review and analyze existing information from diverse areas of earth and climate sciences, palaeobiology and phytogeography to evolve a bio-chronological record of plant species divergence and evolution in the Himalaya. From the analysis we infer the effects of major environmental upheavals on plant diversity in the region. The understanding developed in the following discussion is based on the idea that Himalaya experienced at least five phases of major geophysical upheavals, namely: (i) mega-collision between India and Eurasian plates, (ii) tectonic uplift in phases and progressive landform elevation, (iii) onset of southwest (SW) Indian monsoon, (iv) spurring of arid conditions in Central Asia, and (v) cyclic phases of cooling and warming in the Quaternary. The geophysical upheavals that were potentially disrupting for the ecosystem stability had a key role in providing impetus for biological diversification. The upheavals produced new geophysical environments, new ecological niches, imposed physical and physiological isolation barriers, acted as natural selection sieves and led to the formation of new species. This contribution aims to develop a comprehensive understanding of the plant biodiversity profile of the Himalaya in the context of complex, interconnected and dynamic relationship between earth system processes, climate and plant diversity.

Studying diversity and distribution patterns of species along elevational gradients and understanding drivers behind these patterns is central to macroecology and conservation biology. A number of studies on biogeographic gradients are available for terrestrial ecosystems, but freshwater ecosystems remain largely neglected. In particular, we know very little about the species richness gradients and their drivers in the Himalaya, a global biodiversity hotspot. We collated taxonomic and distribution data of fish species from 16 freshwater Himalayan rivers and carried out empirical studies on environmental drivers and fish diversity and distribution in the Teesta river (Eastern Himalaya). We examined patterns of fish species richness along the Himalayan elevational gradients (50–3800 m) and sought to understand the drivers behind the emerging patterns. We used generalized linear models (GLM) and generalized additive models (GAM) to examine the richness patterns; GLM was used to investigate relationship between fish species richness and various environmental variables. Regression modelling involved stepwise procedures, including elimination of collinear variables, best model selection, based on the least Akaike’s information criterion (AIC) and the highest percentage of deviance explained (D²). This maiden study on the Himalayan fishes revealed that total and non-endemic fish species richness monotonously decrease with increasing elevation, while endemics peaked around mid elevations (700–1500 m). The best explanatory model (synthetic model) indicated that water discharge is the best predictor of fish species richness patterns in the Himalayan rivers. This study, carried out along one of the longest bioclimatic elevation gradients of the world, lends support to Rapoport’s elevational rule as opposed to mid domain effect hypothesis. We propose a species-discharge model and contradict species-area model in predicting fish species richness. We suggest that drivers of richness gradients in terrestrial and aquatic ecosystems are likely to be different. These studies are crucial in context of the impacts of unprecedented on-going river regulation on fish diversity and distribution in the Himalaya.