Grazing Impacts on the Diversity and Composition of Alpine Rangelands in Northwest Yunnan

Aims The eastern Himalayan region of southwest China represents the world’s most biodiverse temperate region as well as a cultural hot-spot undergoing rapid cultural and ecological change.This area represents the center of origin for many plant groups including horticulturally valuable species of Pedicularis,Rhododendron and Primula.alpine meadows here also provide summer pastures for Tibetan yak herders and the source for important medicinal plants.stocking levels for livestock here have quadrupled over the last five decades and shrubs are encroaching into many historical rangelands.Yak herders voice concerns over both shrub encroachment and shrinking grasslands.in this study,we sought to determine:(i)are alpine rangelands in Deqin County overgrazed and degraded?(ii)What are the local impacts of grazing on plant diversity and community composition?and(iii)which environmental variables covary with these differences in species composition across the grazing gradient?Methods To examine the ecological impacts of grazing in Deqin County,northwest Yunnan and assess its long-term sustainability,we used county records to determine historical population and livestock numbers,confirmed the results of interviews by Haynes(2011)and surveyed plant species richness and cover along a grazing gradient extending away from herder huts.along these transects,we sampled 1 m2 quadrats at 5 m intervals,noting species present and per-cent cover for vascular plants,grasses,sedges,rushes,moss,lichen,exposed rock,bare ground and feces.We also measured the average and maximum plant height within each quadrat.We then computed species richness for each of the 38 transects,calculating alpha and beta diversities.We used one-way aNoVas to compare mean species richness values and average and maximum plant height across grazing intensities.To chart changes in composition along the 100m gradient,we also plotted the percent cover of graminoid,forb,shrub and bare ground versus distance from the hut.We applied Nm ordi-nation to relate community patterns to environmental variables and grazing intensity using distances to determine species groupings.Important Findingslivestock impacts are clearly evident with proportions of grass and bare ground decreasing,shrubs increasing and forbs maintaining even cover with increasing distance from the huts.in comparison with earlier surveys of sites farther from huts,we found reduced plant cover and diversity.Plant species richness almost doubles with increasing distance from herder huts from 9.9 to 19.3 species per 1 m2 quadrat.an ordination of species and environmental variables demonstrates that grazing strongly affects plant community com position across these plots with strong impacts on palatable plants.if herd sizes remain large and suitable areas for grazing continue to decline,the cumulative impacts of grazing appear likely to degrade the rich diversity of the region and reduce rangeland quality,threatening its ability to sustain current grazing levels.

Mixed reproduction strategy and polyploidy facilitate dominance of Kobresia pygmaea on the Tibetan Plateau

Aims The sedge Kobresia pygmaea is the dominant species of high-altitude pastures in Tibet,and it is the most important source of forage in animal husbandry.We present the first comprehensive reproduction study for this perennial key species that adopts a molecular approach and tests how sexual and vegetative reproduction,as well as ploidy,relate to survival and dominance under harsh conditions.Methods We assessed inflorescence numbers of K.pygmaea across two Tibetan alpine pastures with differing grazing regimes.Germination was tested in untreated diaspores and then following mechanical and chemical scarification.In a 4-year experiment,we assessed diaspore viability and seed bank formation.Using eight microsatellite markers,we recorded multilocus genotypes in hierarchical grids and measured their ploidy using flow cytometry.Adjusted analysis of variance models were used to analyse data on sexual reproduction,while the complement of the Simpson index and the Shannon diversity index were used to characterize the spatial distribution of multilocus genotypes and clonal richness.Important Findings Inflorescence production was high and differed significantly between years(2010:617±460 SD;2012:2015±1213 SD)but not between grazing regimes.Diaspore viability was high(94%)and gradually decreased after 3 and 4 years of storage in the soil.Diaspores not exposed to further scarification failed to germinate,while mechanical and chemical(H2SO4)scarification increased germination to 9 and 44%,respectively.Clonal diversity was high,although in situ germination was rarely observed.Multilocus genotypes intersected and covered a mean area of 0.74 m2.Most individuals were found to be tetraploid,with only 0.8%of all ramets being triploid.We conclude that K.pygmaea survives on the Tibetan Plateau by employing a mixed reproduction strategy involving both sexual and clonal propagation.The species’adaptability and dominance is further facilitated by its polyploidy.As pasture restoration using diaspores would be difficult,existing Kobresia pasture should be managed more sustainably.