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

ungrazed areas. I used a randomized block design with two treatments (grazing and ungrazed) and three replicates (lower zone = 3000-3500m; middle zone = 3500-400m; and higher zone = 4000-4500m) making a total of six 30mX 30m plots (2 treatments X 3 replicates). All experimental data was collected over a two-year period starting from the growing season of 2013 to the end of the growing season in 2015. It was difficult to separate the effects of different grazers since there was much overlap in the grazing areas shared by the different livestock and wild species. Cows, bulls, goats, horses and a few yak shared the same pastures in the lower zone (3000–3500 m asl). Sheep, yak, cows, bulls, goats, and horses shared the middle zones (3500–4000 m asl) and yak, sheep and a few horses grazed in the higher zone (4000–4500 m asl). Thus, I studied the combined effects of different grazing species. Impacts of grazing on species diversity and above ground net primary productivity (ANPP) Diversity. In each 30mX30 m plot 12 quadrats (1mX1 m) were randomly laid. I had 36 quadrates in grazed areas (12X 3elevation zones) and 36 in ungrazed areas. Thus, a total of 72 quadrats were laid (24 in each zone/ replicate). Data on species composition and percentage cover was collected from each quadrat for herb species only (forbs and graminoids). The graz- ing pastures I sampled had a negligible amount of woody vegetation and none fell in our quad- rats. In the ungrazed plots there were few shrubs, only along the edges which I anyway exluded to avoid for edge effect.

ANPP. I followed the difference method by McNaughton et al. [53] to calculate ANPP in the grazed area. Twelve temporary movable exclosure cages, 1mX1m in size, were set up in each grazed plot. Thus a total of 36 movable exclosure cages were setup every month (12 cages in 3 elevation zones). After each sampling effort (monthly) these cages were moved to a new location within the grazed plot to account for biomass growth (over a month). The above ground standing biomass (vegetation) was clipped to ground level and collected inside and outside exclosure cages. The collected plant material was oven dried 24 hours at 60˚C and then weighed. The ANPP of grazing plots was calculated using the following formula [53] ANPP ¼ W1g þ ðW2u W1gÞ þ ðW3u W2gÞ þ ðW4u W3gÞ þ ðW5u W4gÞ where Wi is the dry mass weight of above ground standing biomass at sample time ti (i = 1, 2, 3, 4, 5: beginning of June, July, August, September, October respectively), u (ungrazed) and g (grazed) represent samplings inside and outside the exclosure cages, respectively. In ungrazed areas twelve 1mX1m quadrats were laid and biomass was collected at peak standing crop (annually). Data analysis Diversity indices—species richness (S), shannon index (H), simpson diversity index (D) and pielous’s evenness (J) were calculated for plant species in grazed and ungrazed quadrats in each elevation zone and for all quadrats (all elevations and grazing treatments combined). Pro- portional dominance (PD) of a species was calculated as a function of relative density and fre- quency (cover). PD ¼ Ni N

��fi where PD is the proportional dominance of species i, Ni is the percent cover of species i in all locations, N is the percent cover of all species in all locations, and fi is the frequency of plots at which species i occurs. The Kruskal-Wallis test was used to calculate significance for difference between diversity indices and ANPP in grazed and ungrazed areas and different elevation zones. To compare the differences between assemblages in terms of rarity (Leroy’s rarity index [54,55]), heterogeneity of the grassland community (Menhinick index [56]), evenness 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 5 / 19