TheKobresia pygmaeaecosystem of the Tibetan highlands – origin, functioning and degradation of the world’s largest pastoral alpine ecosystem
Authors: Miehe Georg , Schleuss Per-Marten , Seeber Elke , Babel Wolfgang , Biermann Tobias , Braendle Martin , Chen Fahu , Coners Heinz , Foken Thomas , Gerken Tobias , Graf Hans-F. , Guggenberger Georg , Hafner Silke , Holzapfel Maika , Ingrisch Johannes , Kuzyakov Yakov , Lai Zhongping , Lehnert Lukas , Leuschner Christoph , Liu Jianquan , Liu Shibin , Ma Yaoming , Miehe Sabine , Mosbrugger Volker , Noltie Henry J. , Opgenoorth Lars , Schmidt Joachim , Spielvogel Sandra , Unteregelsbacher Sebastian , Wang Yun , Willinghöfer Sandra , Xu Xingliang , Yang Yongping , Zhang Shuren , Wesche Karsten 
Published: May 2017

AbstractKobresiapastures in the eastern Tibetan highlands occupy 450000 km2and form the world’s largest pastoral alpine ecosystem. The main constituent is an endemic dwarf sedge,Kobresia pygmaea, which forms a lawn with a durable turf cover anchored by a felty root mat, and occurs from 3000 m to nearly 6000 m a.s.l. The existence and functioning of this unique ecosystem and its turf cover have not yet been explained against a backdrop of natural and anthropogenic factors, and thus its origin, drivers, vulnerability or resilience remain largely unknown. Here we present a review on ecosystem diversity, reproduction and ecology of the key species, pasture health, cycles of carbon (C), water and nutrients, and on the paleo-environment. The methods employed include molecular analysis, grazing exclusion, measurements with micro-lysimeters and gas exchange chambers,13C and15N labelling, eddy-covariance flux measurements, remote sensing and atmospheric modelling.The following combination of traits makesKobresia pygmaearesilient and highly competitive: dwarf habit, predominantly below-ground allocation of photo assimilates, mixed reproduction strategy with both seed production and clonal growth, and high genetic diversity. Growth ofKobresiapastures is co-limited by low rainfall during the short growing season and livestock-mediated nutrient withdrawal. Overstocking has caused pasture degradation and soil deterioration, yet the extent remains debated. In addition, we newly describe natural autocyclic processes of turf erosion initiated through polygonal cracking of the turf cover, and accelerated by soil-dwelling endemic small mammals. The major consequences of the deterioration of the vegetation cover and its turf include: (1) the release of large amounts of C and nutrients and (2) earlier diurnal formation of clouds resulting in (3) decreased surface temperatures with (4) likely consequences for atmospheric circulation on large regional and, possibly global, scales.Paleo-environmental reconstruction, in conjunction with grazing experiments, suggests that the present grazing lawns ofKobresia pygmaeaare synanthropic and may have existed since the onset of pastoralism. The traditional migratory rangeland management was sustainable over millennia and possibly still offers the best strategy to conserve, and possibly increase, the C stocks in theKobresiaturf, as well as its importance for climate regulation.