Impact of Changes in Land Use and Climate on Agricultural Grassland in the European Alps
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Impact of changes in land use and climate on agricultural grassland in the European Alps A thesis submitted to the Faculty of Biology, University of Innsbruck for the degree of Doctor of Philosophy by Georg Niedrist Supervised by Ulrike Tappeiner Institute of Ecology University of Innsbruck, Austria Erich Tasser Institute for Alpine Environment, EURAC Bozen / Bolzano, Italy November 2015 1 2 Contents 1. Extended Summary ................................................................................... 7 1.1 Introduction ........................................................................................ 7 1.2 Overview on mountain grassland communities in the European Alps ... 8 1.3 Plant diversity responses to land use changes ...................................... 9 1.4 Plant responses to changing climatic variability ..................................10 1.5 Mountain grassland responses to changing climate: A modelling approach .....................................................................................................11 1.6 Mountain grassland responses to changing climate: An experimental approach .....................................................................................................13 1.7 Conclusion and outlook ......................................................................13 1.8 References ..........................................................................................16 2. Plant communities of mountain grasslands in a broad cross-section of the Eastern Alps ...........................................................................................19 3. Plant diversity declines with recent land use changes in European Alps ...33 4. A plant’s perspective of extremes: Terrestrial plant responses to changing climatic variability ..................................................................................51 5. Modeling changes in grassland hydrological cycling along an elevational gradient in the Alps ................................................................................98 6. Down to future: Transplanted mountain meadows react with increasing phytomass and shifting species composition .........................................145 7. Curriculum Vitae ...................................................................................181 8. Additional publications, posters and presentations .................................182 8.1 Peer reviewed publications ..................................................................182 8.2 Book contributions ..............................................................................183 8.3 Oral presentations ...............................................................................184 8.4 Posters ................................................................................................185 9. Contribution statement ..........................................................................186 10. Acknowledgments/Danksagung .............................................................188 3 4 Abstract Mountain pastures and hay meadows represent both a source of livelihood for mountain agriculture as well as a biodiversity hot spot. This PhD thesis investigates the impacts of changes in land use and climate on species composition, water balance and productivity of agricultural grassland. The methods include field investigations (paper 1 and 2), literature reviews (paper 1, 2 and 3), modelling (paper 4) and field experiments (paper 4 and 5). All five studies are based on data from agricultural grasslands in the European Alps; paper 3 also includes data from other ecosystems. In general, the results highlight the diversity of these grasslands both at the plot level (α-diversity, max. 63 species per plot) and landscape level (β-diversity, 39 grassland communities). However, the vulnerability of these ecosystems was also visible, especially to land use intensification (-63.4% loss of species richness). Site conditions such as elevation or inclination were found to be less decisive. We found that increasing temperature influenced species composition, especially at lower elevations. Total species number, however, was not affected, but changes are probably only detectable with long-term observation. Productivity increased significantly with a +3°K scenario at the subalpine elevation, whereas no increase was observed at the foothill elevation. Modelling as well as in-situ measurements indicate that the higher (potential) evapotranspiration at lower elevations causes more and longer drought periods (that override the potential advantage of higher temperature at lower elevations). Late spring seem to be particularly sensitive to such drought events. Extreme events and the effect on plant physiology and phenology are still not fully understood and necessitate interdisciplinary approaches that combine experiments, modeling and long-term observation. 5 6 1. Extended Summary 1.1 Introduction Grassland ecosystems comprise a large proportion of all mountain landscapes worldwide. Grasslands cover two-thirds (i.e. 1.5 million km²) of the Tibetan plateau (Cui and Graf 2009), 37% of Tropical Andes (Tovar et al. 2013). In the European Alps 18% are covered by grasslands (Flury et al. 2013), many of them are agriculturally influenced. Though, the patterns of use are as varied as the global extent; for example, uses range from up to 7 times mown and fertilized meadows in in the pre-alpine lowlands to near-natural grasslands in remote, nutrient-poor areas, between the timberline and nival belt. Grasslands fulfill a wide spectrum of fundamental ecosystem services, depending on their location (inclination, elevation) and management intensity. Intensively used meadows and pastures are valuable for provisioning services such as hay and pastureland (O'Mara 2012). More diverse, colorful, flowering grasslands provide cultural services such as aesthetic aspects (Schirpke et al. 2013). Species-rich grasslands on steep slopes and high elevations fulfill crucial regulating services such as soil stabilization (Tasser et al. 2003) and soil water content regulation (Gross et al. 2014, Obojes et al. 2015). Currently, there are two main drivers that affect grassland species composition and thus their ecological function: 1) Modern changes in land use started in Europe during the industrial revolution and became more substantial after World War II when sociocultural changes, mechanization and rural flight led to radical changes in the structure of mountain agriculture (MacDonald et al. 2000). Consequently, grasslands on steep and poorly accessible sites lost importance for fodder production, while favorable sites (e.g. valley bottom) became more and more intensively managed in terms of cutting frequency and fertilizing (Tappeiner et al. 2008). 2) Rising greenhouse emissions affect grasslands rather indirectly via increasing global temperature and changing precipitation patterns than by rising CO2 concentrations (Dukes et al. 2005). In the European Alps, where temperature has increased by 2°K since 1900, scenarios predict a further increase of 1.5– 4.8°K by the end of the 21st century (IPCC 2013, Gobiet at al. 2014). In contrast to changing land use intensity, the consequences of climate change seem to be 7 less immediate, though they affect grasslands worldwide, from lowlands up to the alpine belt (Song et al. 2012, Cornelius et al. 2013). Both the drivers and the impact of such changes on grasslands have been extensively studied for decades (for reviews see Stoate et al. 2009, Queiroz et al. 2014, Dumont et al. 2015), but many questions are still unanswered. For example, studies on climate and land use change are often based on a single type of grassland or few study sites and are thus limited in their representativeness. Furthermore, it is not clear how extreme events and constant warming affect plant growth (Bahn et al. 2014) or to which extent the effects of higher temperature get compensated or even enhanced by lower soil water availability. This doctoral thesis consists of five studies that investigate some of these open issues. Paper 1 is an overview of the status quo (distribution and abundance) of grassland communities in the European Alps. Paper 2 builds on this database and compares diversity indicators among different land use types, i.e. very intensively used grassland, extremely species-rich meadows, pastures and abandoned areas. Paper 3, while maintaining the focus on grassland, also brings the effects of climate change into question. More in detail, it depicts differences in plant responses between changing mean climatic conditions and extreme events and provide an overview of suitable combined approaches to discriminate between changing climate mean and changing climate variability. The last two papers make use of these combined approaches. In paper 4 we investigate the effect of rising temperature on grassland (hay meadows) vegetation, bringing together a hydrological model with transect observations. In paper 5 we used field experiments along an altitude gradient to study grassland diversity and productivity in response to global warming. Finally, the extended abstract contains concluding remarks and an outlook on remaining open issues. 1.2 Overview on mountain grassland communities in the European Alps Despite or maybe even because of the increasing importance of remote sensing technologies (Franke et al. 2012), reliable ground data remain fundamental for grassland classification and distribution. The study in paper 1 is based on 1883