Spatial variety in vegetation of Potentilla fruticosa rangeland rotationally grazed by yak (Bos grunniens) in warm and cold seasons on the distance to night paddock in northern Qinghai-Tibetan Plateau

Spatial variability in vegetation (cover, height, biomass, species diversity) was evaluated in two seasonally grazed, daytime paddocks (WSP, warm-season paddock; CSP, cold-season paddock; 20 years of grazing history) in Potentilla fruticosa rangeland in northern Qinghai-Tibetan Plateau, focusing on the distance to a night paddock (CP, -50 m; NP, 450 m; MP, 850 m; FP, 1250 m). In WSP, coverage and height of P. fruticosa and the coverage and community height of the understory increased as the distance to the night paddock increased (p0.05). Elymus nutans and Kobresia capillifolia which were tall in height were main species in the FP. The dominance values of Potentilla anserina and Plantago asiatica which were prostrate, trampling-tolerant and avoided by yak increased as the distance to the night paddock decreased. Coverage value of Kobresia humilis increased from the FP to the NP but was smallest in the CP among the measuring points. In CSP, the coverage and plant height of P. fruticosa and understory did not show significant differences among FP, MP and NP. Floristic composition of understory was Gramineous plants, K. capillifolia, Polygonum viviparum, Taraxacum mongolicum, Astragalus adsurgens and others. In the CP, number of plant species decreased steeply and dominance value of P. fruticosa was greatest among the plant species. Biomass of understory plants in WSP was greater in FP (169 gDM/square m) and MP (170 gDM/square m) than NP (101 gDM/square m) and CP (100 gDM/square m) (p0.05), and that in CSP was greatest in FP (402 gDM/square m) and smallest in CP (259 gDM/square m ) (p0.05). Both in WSP and CSP, the values of species density and Simpson, Shannon-Wiener and Pielou evenness indices were greatest in NP and smallest in CP among measuring points (p0.05). It was indicated that, in P. fruticosa rangeland rotationally grazed in warm and cold seasons by yak, the distance to the night paddock caused spatial variety in vegetation and the influence was especially greater in warm- season grazed paddock than in cold-season grazed one. It is considered that alternative grazing systems should be investigated for maintaining floral diversity and preventing grazing rangeland from deterioration in Qinghai-Tibetan Plateau.