Plants in urban environments in relation to global change drivers at different scales Dissertation Zur Erlangung der Würde des Doktors der Naturwissenschaften des Fachbereichs Biologie der Fakultät für Mathematik, Informatik und Naturwissenschaften der Universität Hamburg vorgelegt von Katharina Johanna Schmidt aus Heidelberg Hamburg 2014 TABLE OF CONTENTS List of figures V List of tables VII Summary 1 Zusammenfassung 5 1 Introduction 11 1.1 Urbanisation 11 1.2 Environmental conditions in urban areas and urbanisation gradients 12 1.3 History of urban ecology 13 1.4 Urban areas and vegetation 14 1.5 Climate change and biodiversity 19 1.6 Hamburg as a case study 23 1.7 Aims and outline of the thesis 27 2 Effects of urban structure on plant species richness in a large European city 31 2.1 Introduction 31 2.2 Methods 33 2.3 Results 38 2.4 Discussion 43 2.5 Acknowledgements 45 3 Plant species distribution clearly reflects the structure of Hamburg (Germany) on a meso-scale 47 3.1 Introduction 47 3.2 Methods 49 3.3 Results 53 3.4 Discussion 58 3.5 Acknowledgements 60 3.6 Appendix 61 4 Floristic mapping data as a proxy for the mean urban heat island 65 4.1 Introduction 65 4.2 Data and Methods 67 4.3 Results and Discussion 73 4.4 Conclusions and Outlook 79 4.5 Acknowledgements 80 5 Plant species diversity in select habitats along an urbanisation gradient 83 5.1 Introduction 83 5.2 Methods 84 5.3 Results 85 5.4 Discussion and Outlook 87 6 Biotic interactions of Senecio inaequidens DC. with native species in its introduced range under climate warming 89 6.1 Introduction 89 6.2 Methods 92 6.3 Results 98 I TABLE OF CONTENTS 6.4 Discussion 105 6.5 Acknowledgements 111 7 General Discussion & Synthesis 113 7.1 Introduction 113 7.2 Defining urbanisation 113 7.3 Plant species richness, distribution and application of floristic mapping data 114 7.4 Possible impacts of climate change on urban vegetation 118 7.5 Applications for biodiversity conservation in urban areas 120 7.6 Outlook 122 8 References 125 Danksagung 147 II LIST OF FIGURES Figure 1.1 Diagram of a schematic urban heat island (UHI) ....................................................... 13 Figure 1.2 Overview of different hypotheses on increased dominance and invasiveness of non- native species .................................................................................................................... 17 Figure 1.3 Diagram of the interaction between global change drivers, mediating drivers and biodiversity ....................................................................................................................... 20 Figure 1.4 a) Location of Hamburg in Germany, b) Geology of Hamburg influenced by glacial periods (Saale-glaciation and Weichsel-glaciation) .......................................................... 23 Figure 1.5 Distribution of land-use and habitat types in Hamburg. ........................................... 24 Figure 1.6 Distribution of a) mean annual temperature [°C] and b) annual precipitation [mm] in Hamburg for the reference period 1971-2000 ................................................................. 25 Figure 1.7 Mean annual cycle of temperature differences [K] in Hamburg ............................... 26 Figure 2.1 Hamburg’s location within Europe and its main land-use distribution ..................... 33 Figure 2.2 Differences in species richness measures between three urbanisation zones ......... 39 Figure 2.3 Distribution of species richness predictor variables for plant species richness ........ 41 Figure 2.4 Plant species richness distribution in Hamburg ......................................................... 42 Figure 3.1 Hamburg’s location within Europe and its main land-use distribution ..................... 50 Figure 3.2 Dendrogram of the seven clusters revealed by cluster analysis of plant species composition of Hamburg .................................................................................................. 54 Figure 3.3 Spatial distribution of the assignment of grid cells to seven clusters revealed by cluster analysis of plant species composition ................................................................... 55 Figure 3.4 RDA with traits as species proxies and environmental variables .............................. 56 Figure 3.5 Variation partitioning of species, genera, communities, and traits data as response variables with environmental and spatial structure matrices as explanatory variables .. 57 Figure 4.1 Urban climate is a superposition of various effects and processes. .......................... 66 Figure 4.2 Example predictors for Hamburg, Germany .............................................................. 71 Figure 4.3 Mean Ellenberg indicator values for temperature (EITm) for different local climate zones (LCZs) ...................................................................................................................... 74 V LIST OF FIGURES Figure 4.4 Mean heat island intensity for Hamburg, Germany, derived from mean Ellenberg indicator values for temperature (UHIEIT) ......................................................................... 75 Figure 4.5 Modelled urban heat island (UHImod, x-axis) of different linear regression models against values from floristic proxy data (UHIEIT, y- axis) in Kelvin ..................................... 78 Figure 5.1 Location of study sites in Hamburg: Riparian and wasteland gradients .................... 84 Figure 5.2 Scatter plots of a) total plant species number, b) soil pH, and c) soil conductivity ... 86 Figure 5.3 Differences in a) total plant species number, b) soil pH, and c) soil conductivity between riparian and wasteland gradients ...................................................................... 86 Figure 6.1 Location of the six study populations within Hamburg and its surroundings ........... 93 Figure 6.2 Differences in a) seed mass between urbanisation intensities and b) germination percentage between urbanisation intensities and temperature treatments................... 99 Figure 6.3 Differences in growth and biomass of Senecio inaequidens in competition with Achillea millefolium in different densities between urbanisation intensities and temperature treatments ................................................................................................. 101 Figure 6.4 Differences in number of plants with flowerheads of Senecio inaequidens in competition with Achillea millefolium in different densities between urbanisation intensities and temperature treatments ........................................................................ 102 Figure 6.5 Differences in length of longest leaf [cm] of Senecio inaequidens between urbanisation intensities, temperature, and herbivory treatments................................. 103 Figure 6.6 Differences in stem diameter [cm] of Senecio inaequidens between temperature and herbivory treatments ...................................................................................................... 103 Figure 6.7 Differences in aboveground and belowground biomass of Senecio inaequidens between urbanisation intensities ................................................................................... 103 Figure 6.8 Differences in pyrrolizidine-alkaloid-content in Senecio inaequidens between urbanisation intensities and herbivory treatment .......................................................... 104 Figure 6.9 Differences in a) induced pyrrolizidine-alkaloid-content and b) number of damaged leaves by snails between urbanisation intensities and temperature ............................. 105 Figure 7.1 Plant species numbers of native and non-native species for different European cities in comparison to Hamburg. ............................................................................................ 115 VI LIST OF TABLES Table 2.1 Descriptive statistics of four species richness measures: total species richness, proportions of non-native, endangered, and thermophilic species ................................. 34 Table 2.2 Descriptive statistics of the plant species richness predictor variables of urban structure, habitat and environmental conditions ............................................................ 36 Table 2.3 Correlation matrix of species richness predictors ...................................................... 38 Table 2.4 Differences in total species number between different degrees of urbanisation in Hamburg (high, medium, low) according to two methods of index division. .................. 38 Table 2.5 Multiple regressions of the effects of species richness predictors on species richness patterns. ............................................................................................................................ 42 Table 3.1 Descriptive statistics of environmental variables ....................................................... 52 Table 3.2 Species numbers of the seven clusters ....................................................................... 54 Table 3.3 Explained variance [%] by two methods of redundancy analysis (RDA) of species, genera, communities, and traits data ............................................................................... 57 Table 3.4 Permutation tests of the explanatory variables’ single fractions from variation partitioning with species and the species proxies genera, communities and traits as response data and environmental and spatial variables as explanatory matrices .......... 57 Table 4.1 Predictors related to the urban heat