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

(McIntosh index [57])and taxonomic distinctness [58,59] (Dstar) the four components of diversity were combined into a single measurement using the DER_algorithm in the EcoIndR package in R [60]. The algorithm calculates the polar coordinates of all samples with all possi- ble combinations for the four indices and then calculates the convex hull and mean Euclidean distances between samples. Each circle represents a quadrat (1mX1m), the size of the circles represents species richness and the color rarity. To explore the response of species composition to grazing treatments and elevation a triangular similarity matrix was constructed using Bray Curtis similarity coefficients based on cover data. The similarity matrix was displayed in an ordination plot using non-metric multi- dimensional scaling (NMDS). The stress function assesses how well the calculated sample rela- tionships are represented in the two-dimensional plot. A lower value (<0.2 commonly accepted) represents a more accurate ordination [61,62]. The Analysis of similarity (ANOSIM) was used to check the degree of dissimilarity of spe- cies across grazing treatments, elevation zones, and treatments within each elevation zone. ANOSIM based on the Bray Curtis similarity matrix was used to check significance levels using a permutation test with 999 simulations. R values close to 1 suggest sites within a group are similar to each other and dissimilar to sites in other groups. While an R value close to "0" suggests an even distribution of high and low ranks within and between groups. A linear

regression was used to examine the relationship between diversity and productivity. All analyses were performed on R. The NMDS and ANOSIM analysis were performed using the vegan package in R [63]. Results Species diversity indices A total of 153 plant species between 3000–4500 m asl were sampled. This included the 66 (S = 13.38 ±5.71),56 (S = 11.42 ±5.01) and 47 (S = 9.38 ±3.41) species found in the lower, mid- dle, and higher zones, respectively. A significantly (p<0.001) higher number of species was found in grazed areas (114 species) than in ungrazed areas (61 species). I sampled 51,48 and 30 species in grazed areas and 22,19 and 22 species in ungrazed areas in lower, middle, and higher zones, respectively. The analysis showed all diversity indices (S,H,D and J) were significantly higher (p<0.001) in grazed quadrats than ungrazed quadrats in all elevation zones combined and in each zone (Fig 2A–2D, Table 1). Grazing had a significant (p<0.001) effect on all diver- sity indices in each elevation zone and all elevation zones combined (Table 1). Unlike grazing, elevation did not have a significant effect on diversity indices (Fig 2F–2I). Results of the ANOSIM indicate statistically significant differences in species composition. There is a significant difference in species composition between grazing treatments in each elevation zone (lower: R = 0.0.911 p<0.001;middle: R = 0.786 p<0.001; higher R = 0.878 p<0.001) (Fig 3C–3E). As would be expected, elevation plays a significant role in species com-

position. Species composition (grazed and ungrazed combined) in different elevation zones showed a significant difference (R = 0.844 p<0.001) (Fig 3B). The ANOSIM R value for graz- ing treatment across all elevations was relatively lower (R = 0.199 p<0.001) suggesting com- paratively more overlap in species compositions in grazed and ungrazed areas (Fig 3). Overall, grazed and ungrazed plots had 14.38% (22) species in common. In the lower, middle and higher zones they shared 7(10.61%), 11 (19.64%) and 5 (10.64%) species, respectively. In addition to S,H,D and J, grazing also affected the other components of diversity (Fig 4). Fig 4 shows high dispersion between grazed quadrats and ungrazed quadrats. Grazed quadrat number 5 in the lower zone (G5) showed the highest values of rarity, heterogeneity, evenness and taxonomic distinctness whereas U14 –ungrazed quadrat number 14 in the middle zone 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 6 / 19