Pastoralism in the highest peaks: Role of the traditional grazing systems in maintaining biodiversity and ecosystem function in the alpine Himalaya

tonnes and the concurrent increase in regeneration of species of high conservation value such as Rhododendron barbatum [41,42]. At the same time, Bhagwat et al. [41] also warned of insig- nificant regeneration of important fodder species and other species of high conservation value such as Quercus spp. coupled with a spread of gregarious species such as Arundinaria maling and Viburum cordifolium. Restriction on free access to forest resources have had significant socio-economic impacts on the herders who were dependent on grazing pastures in the sanc- tuary. Their average net income from livestock was reduced by more than half the pre-ban period, with the source of majority of the incomes now coming from government subsidies and schemes like the National Rural Employment Guarantee Act programme (MGNREGA) for unskilled labor [41,43]. A study on the perception of sedenterized ex-herders from West Sikkim identified loss of traditional livelihoods leading to decreased income and limited land holdings as their main protestations. In addition to socio-economic impacts to herders the grazing ban has had a cascading impact on non-herders [41]. Perceptions of local villagers indicate an increase in human wildlife conflict in the form of crop raids and livestock depreda- tion with over 85% of the households experiencing greater losses in agricultural outputs after the grazing ban [41,43]. Here, I explore the impact of the present pastoral system on high elevation plant species in Lachen valley, Sikkim. The region is of significance for two reasons. First, it falls in one of the

most biodiverse regions of the world, the alpine zone of the Sikkim Himalaya [37]. Second transhumant pastoralism has been practiced in the region for centuries with the indigenous communities directly dependent on the biodiversity of their surrounding for livestock hus- bandry, water storage and provisioning, and the collection of medicinal, aromatic, and edible plants [38,44,45]. I address two broad questions: 1. What is the impact of the traditional grazing system on plant diversity and ecosystem func- tion (using aboveground net primary productivity as an integrative measure of ecosystem function [46,47]) in the high-elevation alpine Himalaya? 2. How does grazing maintain biodiversity and ecosystem function in the region? I first analyze the impact of grazing on diversity and productivity. I then discuss the role of grazing in maintaining high biodiversity and ecosystem function. Finally, I conclude by identi- fying further knowledge needs and propose recommendations for an improved grazing policy to protect the rich yet vulnerable biodiversity of the region. Materials and methods Study area The study was conducted in Lachen valley in the North district of the state of Sikkim in India. Necessary field research permits were obtained from the Department of Forest, Environment & Wildlife Management, Government of Sikkim, India—Letter No. 16/SRO/F dated 20/04/ 2010 and Ref. No. 101 /PCCF/F dated 03/02/2012. Sikkim, in the Eastern Himalayan region (Fig 1), is the second smallest (7096 km2) and the least populous state of India. The alpine

zone of Sikkim has unique biodiversity since it also falls in the transition zone of two biogeo- graphic regions, namely the central Himalaya region and the southern fringe of the Palearctic region [48]. Lachen valley lies within the alpine zone of Sikkim and shares an international border with the Tibet Autonomous Region (TAR) of China. The valley is among the few places where open grazing is permitted in the state of Sikkim [40]. It is inhabited by two pastoral communities—the yak and sheep herders, the Dokpas and the agro-pastoral Lachenpas. PLOS ONE Role of the traditional grazing systems in maintaining biodiversity and ecosystem function in alpine Himalaya PLOS ONE | https://doi.org/10.1371/journal.pone.0245221 January 7, 2021 3 / 19