The Shaping of Tibetan Grasslands
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The shaping of Tibetan grasslands: Combined effects of livestock-grazing and environment – a multi-site, interdisciplinary study Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.) der Naturwissenschaftlichen Fakultät I – Biowissenschaften – der Martin-Luther-Universität Halle-Wittenberg, vorgelegt von Frau Yun Wang geb. am 08.03.1984 in Kunming, Yunnan, P.R. China Gutachter/in: 1. Prof. Dr. Isabell Hensen 2. PD. Dr. Karsten Wesche 3. Prof. Dr. Peng Luo Halle (Saale), 14.06.2016 Copyright notice Chapters 3 to 6 have been published in, submitted to or in preparation for submitting to international journals. Only the publishers and the authors have the right for publishing and using the presented materials. Any re-use of the presented materials should require permissions from the publishers and the authors. Norther Winslow: I've been working on this poem for 12 years. Young Ed Bloom: Really? Norther Winslow: There's a lot of expectation. I don't wanna disappoint my fans. Young Ed Bloom: May I? Young Ed Bloom: [Edward reeds the poem on the notebook] “The grass so green Skies so blue Spectre is really great!” Young Ed Bloom: It's only three lines long….. Norther Winslow: This is why you should never show a work in progress. Big Fish (2003) Content Content Extended summary ................................................................................................................................ I Ausführliche Zusammenfassung ........................................................................................................... V Acknowledgements ............................................................................................................................. IX Abbreviations ...................................................................................................................................... XI Chapter 1 Introduction .......................................................................................................................... 1 Chapter 2 Study region and general methodology .............................................................................. 11 1 Geology, climate and soils ........................................................................................................... 12 2 Grassland types, plant and fauna diversity .................................................................................. 15 3 Grazing systems, livestock and management .............................................................................. 19 4 General methodology ................................................................................................................... 25 Chapter 3 Literature review ................................................................................................................ 31 Chapter 4 Responses of vegetation and soils ...................................................................................... 55 Chapter 5 Responses of multiple indicators........................................................................................ 75 Chapter 6 Responses of hyperspectral data ........................................................................................ 99 Chapter 7 Synthesis–lessons for different indicator groups.............................................................. 125 7.1 Responses of vegetation.......................................................................................................... 125 7.2 Responses of soil conditions ................................................................................................... 126 7.3 Responses of fauna indicators ................................................................................................. 127 7.4 Responses of hyperspectral data ............................................................................................. 127 7.5 Lessons from interdisciplinary approach ................................................................................ 128 7.6 Management implications ....................................................................................................... 129 Chapter 8 Conclusion ....................................................................................................................... 133 Chapter 9 Outlook–the way ahead for further studies ...................................................................... 134 Erklärung über den persöhnlichen Anteil an den Publikationen....................................................... 139 Curriculum Vitae .............................................................................................................................. 141 Eigenständigkeitserklärung ............................................................................................................... 143 Extended summary I Extended summary Livestock grazing is the dominant land use on Central Asian grasslands, where the increasing grazing pressure has been widely blamed as the main cause of grassland degradation. Livestock directly reduce plant aboveground biomass and change plant species composition through foraging. Trampling compacts soils and often negatively affects soil physical conditions, which may further influence soil carbon (C), nitrogen (N) and other nutrient contents. Livestock-mediated nutrient redistribution might reshape plant communities; in turn, grazing-induced alterations in plant communities also feedback on soil properties. Grazing influences animal communities by changing vegetation structure, soil conditions, and disturbing food chains. Previous empirical studies from semi-arid grasslands have revealed that plant communities are not mainly structured by livestock impacts as classical equilibrium theories proposed. Climate conditions, especially precipitation patterns, might strongly control plant growth and population dynamics at certain temporal and spatial scales. Interactions with climate and topographic conditions could mitigate or intensify grazing effects by changing resource availability (e.g. food, water, light, heat) or modifying relationships within and among trophic levels. Disentangling environmental impacts from livestock grazing effects is not only important to understand rangeland theories, but also critical for grassland management and conservation. As one of the largest grassland regions in the world, Tibetan grasslands host enormously varying physical environments along with an evolutionary history of grazing by large herbivores including wild, and now predominantly domestic animals. Grassland health in this region is relevant for local livelihoods and the environment of surrounding regions. The broadly held perception that increased grazing leads to extensive grassland degradation across the plateau is rooted in equilibrium theories and has overlooked the importance of environmental variability as non-equilibrium theories highlight. Accordingly, policies for grassland conservation and restoration mostly focus on reducing livestock numbers and restricting mobility of pastoralism. Besides the insufficient theoretical considerations, several methodological problems exist in previous degradation assessments of Tibetan grasslands. First, field studies mostly focus on controlled grazing experiments from single sites, and hardly consider interactions with physical environmental factors. Even among those which do, the limited study duration often Extended summary II restricts the possibility of detecting long-term responses. Whether the typically employed clipping could represent the natural grazing situation is still questionable. Second, large-scale studies are typically based on remote sensing data or modelling approaches, thus are often too generalized, simplified and lack of proper field calibrations. Although there are several multi-site field surveys on plant communities and soil conditions along large environmental gradients, grazing effects are rarely taken into account. Finally, inconsistent definitions and standards of degradation and non-standardized sampling methods make the interpretation of general patterns difficult, as shown from the extensive review focused on grazing effects on vegetation and soils (Chapter 3). Baring these inadequate aspects in mind, this thesis presented a multi-site study on five indicator groups (vascular plants–hereafter plants, small mammals, ants, soils and hyperspectral data) across two main habitats (alpine meadow, steppe) and one transitional ecotone (steppe-meadow) on Tibetan grasslands. Four levels of livestock activity (piosphere directly adjacent to herder camps, heavy, moderate and light grazing) were considered. Plant communites (626 species, six functional groups) and soil conditions (eight chemical properties) from 173 plots/28 sites were compared among all these four levels. In the course of partner projects, ants (15 species), small mammals (15 species) and hyperspectral data (15 indices) were sampled from heavy-light grazing pairs at 18 sites within the same standardized sampling strategy (Chapter 2). Environmental factors include climate conditions of mean annual precipitation total (hereafter precipitation, P, 110–660 mm) and the coefficient of interannual variation (cvP, 14–42%), mean annual temperature (hereafter temperature, T, −6.1–3.2 °C ), accumulative temperature above 0 °C (acT0, 478–1816 °C ) and shortwave incident radiation (srad, 190–260 w/m2); and topographic conditions of elevation (Elev, 2820–5150 m), inclination (incl, 0–16 °), relief positions