- A study from Sikkim’s Lachen valley finds that areas grazed by livestock had greater plant species diversity and productivity compared with ungrazed areas.
- The findings suggest that a current ban on grazing in the region may not achieve the goal of conserving biodiversity.
- However, more research on the impacts of specific livestock, altered herd sizes and grazing intensities are needed before considering the reintroduction of grazing in the region.
A new study from pastures in the alpine rangelands of the Eastern Himalayan state of Sikkim, that enacted a grazing ban in 1998, finds that traditional pastoral grazing enhances plant species diversity and vegetation productivity. However, further research is needed to understand the role of livestock and wild ungulates on ecosystem structure and function before revisiting the present ban on grazing in the region, according to the author.
“The benefits of traditional free-ranging pastoralism cannot be ignored and a holistic approach is needed to conserve the rich biodiversity of the region,” said study author Tenzing Ingty, an ethnobiologist who is currently a Ph.D. candidate in the Department of Biology at the University of Massachusetts in the United States.
Rangelands of the Himalayas are a global biodiversity hotspot and provide a myriad of ecosystem services from carbon sequestration and water storage to maintaining biodiversity and providing livelihoods to pastoral communities. For millennia, pastoralists have been inhabiting rangelands and these socio-ecological systems have coevolved. While the rangelands of Sikkim—one of the most biodiverse regions of the world—occupy a mere 0.006 percent of rangelands globally, they harbour almost 60 percent of global alpine plant families.
In 1998, Sikkim enacted a ban on open grazing in reserved forests in response to growing human pressures on grazing lands and in protected forests. Lachen valley in the North district of the state, among other areas, was exempt from the ban and it is one of the few places where grazing still occurs. Yak herders, the Dokpas, and sheep herders, the agro-pastoral Lachenpas, inhabit the valley. The Dokpas travel to the Tibetan Plateau in the winter for snow-free pastures whereas the Lachenpas retreat to lower elevations in the winter.
The grazing ban has had both positive and negative effects as reported by various studies. On the one hand, carbon stocks shot up along with an increase in the regeneration of some species of high conservation value. However, monocultures in lowlands have risen and there has been a drop in manure production, which is important as Sikkim exclusively practices organic farming. Notably, herders suffered a decline in income from livestock. Local villagers have also perceived a rise in incidences of human-wildlife conflict.
Higher plant species diversity and productivity
The study examines the impact of traditional grazing on high-elevation plant species diversity and ecosystem functioning in Lachen valley. Ingty sampled vegetation in plots from grazed and ungrazed pastures along three different elevation zones for two years. He quantified plant species diversity using various indices and as an integrative measure of ecosystem functioning, he calculated aboveground net primary productivity (amount of plant biomass accumulated over a specific period of time).
Grazing occurred for at least two decades in the grazed areas while the ungrazed pastures had not been grazed upon for 10 years and were set aside by locals for hay formation. Species such as yak, sheep, cows, goats, horses and bulls shared the grazed pastures, with a slightly different mix at each elevation.
In all elevation zones, grazed areas had greater plant species diversity and productivity than the ungrazed areas. Species richness in grazed areas doubled in the middle and lower zone and increased by 61.5 percent in the high-altitude zone. Aboveground net primary productivity was on average 32 percent higher in grazed areas than in ungrazed areas.
Grazing could drive higher plant species diversity because of the role of livestock in dispersing seeds, allowing less-dominant species to compete and creating heterogeneity in the habitat by recycling nutrients from larger areas and concentrating it into small patches through their dung and urine, explained Ingty. A more diverse plant community may drive higher aboveground net primary productivity through various mechanisms.
Species diversity and grazing: To graze or not to graze?
Past studies in the Himalayas on the effect of grazing on species diversity have been varied: some have shown a decrease in species diversity in response to grazing while others have shown a rise. Factors such as the intensity of grazing play a role in determining the impact on diversity. “Grazing pressure is a function of the number and types of grazers (livestock and wild herbivores),” explained Ingty. In general, moderate grazing has been shown to increase species diversity whereas high grazing pressure leads to lower diversity, he said.
The findings of this study suggest that a complete ban on grazing may not meet the objective of conserving local and regional biodiversity, said Ingty, adding that a more holistic approach that is mutually beneficial for conservation and livelihoods is needed. But more research is needed before any changes are considered in the current grazing policies. He suggests conducting experiments “reintroducing grazing in a small area where grazing was banned to better understand the carrying capacity of pastures and the impacts of altered herd sizes and, specific livestock and grazing intensities.”
Ingty also cautions that “pastoralism is associated with numerous other spillover effects such as illegal timber and fuelwood collection, medicinal plants (often rare and endemic) collection and the negative effects of overgrazing.”
The study is interesting, said G.S. Rawat, ecologist and former Dean at the Wildlife Institute of India. “Grazing by wild ungulates such as wild yak, chiru, blue sheep and nomadic pastoralism is said to be much more ancient on the Tibetan plateau or Trans-Himalaya. Therefore, those ecosystems are possibly more resistant to grazing,” explained Rawat.
“On the other hand, southern slopes of the Himalaya are still evolving and grazing by wild ungulates and also pastoral practices may be less pronounced. Heavy animals such as yak and cattle have not evolved in these ecosystems. Hence, their ability to withstand grazing may be different.”
Based on his past observations from the Valley of Flowers in the Western Himalayas, Rawat and his co-author stated in a 1993 paper that while moderate grazing may lead to an increase in plant diversity in some areas, the desired species may not always arise in the grazed areas. He believes that “at least some areas should be kept free from livestock grazing and set aside for natural grazing by wild herbivores.”
Ingty, T. (2021). Pastoralism in the highest peaks: Role of the traditional grazing systems in maintaining biodiversity and ecosystem function in the alpine Himalaya. PLoS ONE, 16(1), e0245221.
Banner image:Lashar in Lachen valley, Sikkim. Photo by Tenzing Ingty.