RANGELAND DYNAMICS IN THE HIMALAYA

Rangelands

Rangelands cover around half of the planet’s landmass and provide vital ecosystem services to over a quarter of humanity. Rangelands are also recognized for their high biodiversity, including numerous endangered and endemic species, as well as habitat connectivity between protected forests. In much of the developing world, rangelands are inhabited by pastoral communities. Pastoralism that has existed for millennia has impacted the evolution of many rangelands, from the biodiverse rich African savanna to the highest elevations in the Tibetan steppe. Pastoralists and the rangelands they inhabit thus form complex socio-ecological systems that have co-evolved across different geographies, biodiversity and climates. Many pastoralists have been blamed, often wrongly, for rangeland degradation and targeted for “modernization” programs such as sedentarization.


Rangelands of the Himalaya

Rangelands in the Himalaya, a global biodiversity hotspot, form the largest land-use system and provides numerous ecosystem services to pastoral communities. The Himalaya is the source of 10 of the largest rivers in Asia whose basins feed about one-fifth of humanity. The alpine rangelands of the Himalaya thus play a vital role in retaining critical ecosystem services such as carbon sequestration, water storage, and provisioning, maintaining biodiversity, and food security and livelihoods. Despite its importance, a report on high elevation rangelands of the Himalaya underlines numerous threats such as invasive species, inappropriate management, and development policies, overgrazing , and climate change.

Our work in the Himalayan rangelands

Our work explores the impact of the traditional pastoral system on high elevation plant species in Lachen valley, one of the few regions of Sikkim where the grazing ban was not implemented. In 1998, the Indian state of Sikkim, in the Eastern Himalaya, enacted a grazing ban in response to growing anthropogenic pressure in pastures and forests that was presumably leading to degradation of biodiversity.

Results demonstrate that grazing significantly contributes to greater plant species diversity and ecosystem function. The multidimensional scaling and ANOSIM (Analysis of Similarities) pointed to significant differences in plant species assemblages in grazed and ungrazed areas. Further, ecosystem function is controlled by grazing, rainfall, and elevation. Thus, the traditional transhumant pastoral system may enhance biodiversity and ecosystem function. I argue that a complete restriction of open grazing meets neither conservation nor socioeconomic goals. Evidence-based policies are required to conserve the rich and vulnerable biodiversity of the region


Study site in Lachen Valley, North Sikkim. One of the few regions of the state where free-range grazing occurs.

https://doi.org/10.1371/journal.pone.0245221.g003

Non-metric multidimensional scaling (NMDS) based on Bray Curtis similarity matrix of plant communities. Analysis of similarity (ANOSIM) statistic R and its significance are indicated in boxes. Groups are represented by ellipses (95% CI around centroids). NMDS ordination of 153 species grouped according to grazing treatment (A) and elevation gradient (B); NMDS ordination of species in lower (C), middle (D), and higher elevation (E) zones respectively grouped according to grazing treatment

https://doi.org/10.1371/journal.pone.0245221.g004

Spatial distribution of 72 quadrates based on four diversity indices (rarity- Leroy’s rarity index, Menhinick -heterogeneity, Dstar-taxonomic distinctness and McIntosh index-evenness). The size of the circles increases with richness, and a color-code (gradient) is used to indicate the rarity index. Circles are labelled G for grazed quadrates and U for ungrazed quadrates. Numbers in circles represent quadrate numbers (1-12 Lower zone, 13-24 mid zone, 25-36 Higher zone)


https://doi.org/10.1371/journal.pone.0245221.g002

A-J Boxplots of diversity indices and above ground net primary productivity (ANPP) for 153 species sampled from 72 plots. A-E diversity indices and ANPP in grazed vs ungrazed plot in all elevations combined (All) and in each elevation zone (lower, middle and higher). F-J diversity indices and ANPP in each elevation zone for all species. K -ANPP in each elevation zone per month (June to October). L -Linear relationship between species richness (quadrate scale) and ANPP in lower, middle and higher elevation zone quadrates. R2 values indicated. *** represents statistical significance (p<0.01).