Research Collection Doctoral Thesis Impacts of Climate Change on Alpine Grassland Ecosystems: Responses in Structure and Function Author(s): Schmid, Samuel Publication Date: 2017 Permanent Link: https://doi.org/10.3929/ethz-b-000224238 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library DISS. ETH NO. 24075 IMPACTS OF CLIMATE CHANGE ON ALPINE GRASSLAND ECOSYSTEMS: RESPONSES IN STRUCTURE AND FUNCTION A thesis submitted to attain the degree of DOCTOR OF SCIENCES of ETH ZURICH (Dr. sc. ETH Zurich) presented by SAMUEL SCHMID Dipl. Ing.-Agr. ETH, ETH Zurich born on 30.10.1979 citizen of Vordemwald (AG) and Suhr (AG) accepted on the recommendation of Prof. Dr. Nina Buchmann Prof. Dr. Andreas Lüscher Prof. Dr. Michael Scherer-Lorenzen 2017 Contents Contents 1 Definitions ....................................................................................................................................... 5 2 Summary ......................................................................................................................................... 7 3 Zusammenfassung ......................................................................................................................... 11 4 General introduction ..................................................................................................................... 15 4.1 High elevation life zone ......................................................................................................... 15 4.1.1 Life conditions ............................................................................................................... 15 4.1.2 Climate .......................................................................................................................... 16 4.1.3 Vegetation and elevational zonation ............................................................................ 17 4.2 Alpine grassland .................................................................................................................... 20 4.2.1 Sward communities in the drought experiment ........................................................... 20 4.2.2 Ecosystem services of alpine grassland ......................................................................... 21 4.3 Study sites ............................................................................................................................. 21 4.3.1 Albula and Furka Pass .................................................................................................... 21 4.3.2 Experimental sites and observational areas ................................................................. 23 4.4 Climate change ...................................................................................................................... 26 4.4.1 Global and regional climate change .............................................................................. 26 4.4.2 Climate change impacts on plant communities ............................................................ 26 4.4.3 Drought impacts on grassland ecosystems ................................................................... 27 4.4.4 Effects of climate change on alpine ecosystems ........................................................... 28 4.4.5 Consequences of a warmer climate in alpine ecosystems ............................................ 28 4.4.6 Consequences of a drier climate in alpine ecosystems................................................. 30 4.5 Plant stress ............................................................................................................................ 31 4.5.1 Conceptions of stress .................................................................................................... 31 4.5.2 Drought stress ............................................................................................................... 32 4.5.3 Physiological responses during drought stress ............................................................. 33 4.5.4 Survival of drought stress .............................................................................................. 33 4.6 Drought experiment .............................................................................................................. 35 4.6.1 Experimental design ...................................................................................................... 35 4.6.2 Rainout shelter design and sampling plot ..................................................................... 36 4.6.3 Rainfall manipulation .................................................................................................... 37 4.6.4 Assessment of the drought simulation with micro-meteorological measurements .... 38 1 Contents 4.6.5 Classification of the simulated droughts in relation to climate change scenarios and other drought experiments .......................................................................................................... 41 4.7 Thesis outline ........................................................................................................................ 48 4.8 References ............................................................................................................................ 49 5 Changes in vegetation structure of alpine grassland in response to three years of simulated summer drought are highly site-dependent (Study 1) ......................................................................... 59 5.1 Abstract ................................................................................................................................. 59 5.2 Introduction .......................................................................................................................... 60 5.3 Methods ................................................................................................................................ 63 5.3.1 Study sites ..................................................................................................................... 63 5.3.2 Experimental design and drought simulation ............................................................... 64 5.3.3 Data collection .............................................................................................................. 65 5.3.4 Data analysis ................................................................................................................. 66 5.4 Results ................................................................................................................................... 69 5.4.1 Canopy structure .......................................................................................................... 69 5.4.2 Soil surface structure .................................................................................................... 70 5.4.3 Ground protection (overlay canopy layer, soil surface) ............................................... 70 5.4.4 Vegetation dry matter .................................................................................................. 71 5.4.5 Methods comparison .................................................................................................... 71 5.5 Discussion ............................................................................................................................. 79 5.5.1 Structural variability in alpine grassland....................................................................... 79 5.5.2 Alpine grassland structural responses to summer drought ......................................... 80 5.5.3 Erosion susceptibility in alpine grassland ..................................................................... 85 5.5.4 Non-destructive assessment of structural responses to summer drought in alpine grassland vegetation ..................................................................................................................... 88 5.6 Conclusions ........................................................................................................................... 90 5.7 References ............................................................................................................................ 91 6 Shift from above- to below-ground biomass production in alpine grassland to resist recurring experimental summer droughts (Study 2)............................................................................................ 97 6.1 Abstract ................................................................................................................................. 97 6.2 Introduction .......................................................................................................................... 98 6.3 Methods .............................................................................................................................. 102 6.3.1 Study sites ................................................................................................................... 102 6.3.2 Experimental design and drought simulation ............................................................. 103 6.3.3 Data collection ............................................................................................................ 104 2 Contents 6.3.4 Data analysis ...............................................................................................................