Durham E-Theses The ecological eects of slope and aspect in chalk grassland Bennie, Jonathan James How to cite: Bennie, Jonathan James (2003) The ecological eects of slope and aspect in chalk grassland, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/4017/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk A copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. The Ecological Effects of Slope and Aspect in Chalk Grassland Jonathan James Bennie B.A. M.Sc. School of Biological and Biomedical Sciences University of Durham 2003 This thesis is submitted in candidature for the degree of Doctor of Philosophy 7 'm- 11 Frontispiece: South-facing sward on Hambledon Hill. Ill Table of Contents List of figures vii List of tables x List of plates xi Declaration xii Abstract xiii Acknowledgements xiv Notes on nomenclature used in this thesis xv Glossary of acronyms xvi Chapter 1: Introduction and Aims 1 1.1 Introduction to slope and aspect 1 1.1.1 Slope, aspect and microclimate 1 1.1.2 Slope and aspect in ecological studies 1 1.1.3 Slope and aspect in chalk grassland 2 1.2 Scope and aims of thesis 3 Chapter 2: Background to Study 6 2.1 Introduction 6 2.2 Literature review 6 2.2.1 The effects of climate on the distribution of plants 6 2.2.2 Physiological mechanisms 11 2.2.3 Microclimate and topography in grasslands 25 2.2.4 Topography, soils and vegetation in calcareous grasslands 28 2.3 Further analysis of Perring's data 32 2.3.1 The data set 32 2.3.2 Methods of analysis 33 2.3.3 Results 35 2.3.4 Discussion of analyses 47 2.4 Summary of chapter 2 49 iv Chapter 3: Field sites and climate measurement 51 3.1 Introduction 51 3.2 Metliods 51 3.3 Acquisition of digital terrain models (DEM) 53 3.3.1 Hambledon Hill 53 3.3.2 Sylvan Dale 54 3.4 Methods - Macro- and microclimate measurement 60 3.4.1 Measurements at AWS sites .60 3.4.2 Mobile dataloggers 61 3.4.3 Buried temperature loggers 61 3.4.4 Soil moisture measurement 64 3.5 Climatic observations at field sites 65 3.5.1 Comparison of AWS climate between sites 65 3.5.2 Diurnal patterns in radiation and temperature 69 3.5.3 Temperature and altitude at Hambledon Hill 71 3.5.4 "Frost hollow" effect at Sylvan Dale 72 3.5.5 Comparison of temperatures on different slopes 73 3.5.6 Observed patterns in soil temperature 75 3.5.7 Observed patterns in soil moisture 77 3.6 Summary of Chapter 3 79 Chapter 4: Modelling topographic microclimate 81 4.1 Introduction 81 4.2 Approach to modelling topographic microclimate 81 4.2.1 Physical/empirical approaches 81 4.2.3 Landscape-scale variation in screen height climate 82 4.3 Model development 83 4.3.1 Solar radiation 83 4.3.2 Photosynthetically active radiation (PAR) 87 4.3.3 Net radiation 87 4.3.4 Near surface temperatures 90 4.3.5 Soil moisture 100 4.4 Model testing and validation 105 4.4.1 Solar radiation 105 4.4.2 Sward temperature 108 V 4.4.3 Soil temperature 110 4.4.4 Soil Moisture 113 4.5 Discussion 117 4.6 Summary of chapter 4 120 Chapter 5: Field experiments and observations 122 5.1 Introduction 122 5.2 Nutrient cycling on contrasting slopes 122 5.2.1 Calcareous grassland soils 122 5.2.2 Nutrient availability in chalk grassland 123 5.2.1 Methods 125 5.2.2 Results 131 5.2.3 Conclusions 140 5.3 Gas-exchange measurements in four chalk grassland species 143 5.3.1 Soil moisture, photosynthesis and water-use efficiency 143 5.3.2 Methods 144 5.3.3 Results 147 5.3.4 Conclusions 149 5.4 Germination of selected chalk grassland species 150 5.4.1 Microclimate and germination 150 5.4.2 Materials and Methods 151 5.4.3 Results 156 5.4.4 Conclusions 156 5.5 Summary of chapter 5 159 Chapter 6: Vegetation analysis 161 6.1 Introduction 161 6.2 Methods 162 6.2.1 Vegetation survey 162 6.2.2 Microclimatic variables 165 6.2.3 Ellenberg and CSR scores 168 6.2.4 Vegetation analysis 168 6.3 Results 169 6.3.1 Qualitative comparison between slopes 169 6.3.2 DCA of sites at Sylvan Dale and Hambledon Hill 173 vi 6.3.3 GAMs of DCA axis 1 and species frequency 177 6.3.4 Vegetation change and topography at Hambledon Hill 1952-2000 183 6.3.5 Change in vegetation plot scores 1952-2000 186 6.4 Discussion 190 6.4.1 Topography, microclimate and vegetation at Hambledon Hill and Sylvan Dale 190 6.4.2 Vegetation change at Hambledon Hill 1952-2000 191 6.5 Summary of chapter 6 196 Chapter 7: General discussion 197 7.1 Introduction 197 7.2 Microclimatic gradients 197 7.2.1 Predicted and observed patterns 197 7.2.3 Limitations of models 199 7.3 Soil gradients 200 7.3.1 Spatial heterogeneity 200 7.3.2 Microclimate and soils 201 7.3.3 Topography and soils 202 7.4 Vegetation gradients 203 7.4.1 The effect of soil moisture on vegetation 204 7.4.2 Species response to microclimate 205 7.7 Topography and vegetation change 207 7.7.1 Vegetation change at Hambledon Hill 1952-2000 207 7.7.2 Topography and future vegetation change 207 References 210 Appendix 1 236 Appendix 2 237 Appendix 3 238 Appendix 4 241 Appendix 5 CD Vll List of figures Figure 2.1: Distributions of selected species, from Perring (1959) 31 Figure 2.2: Ordination of first two DCA axes 36 Figure 2.3: Ordination of first two DCA axes; CSR indices 37 Figure 2.4: Ordination of first two DCA axes; Ellenberg indices 38 Figure 2.5: Triangular C-S-R plot of Grime's indices for each plot 39 Figure 2.6: DCA axis 1 GAM partial residual plots 42 Figure 2.7: DCA axis 2 GAM partial residual plots 43 Figure 2.8: Hippocrepis comosa GAM residual plots 44 Figure 2.9: Asperula cynanchica GAM residual plots 45 Figure 2.10: Sanguisorba minor GAM residual plots 46 Figure 1.11: Plantago lanceolata GAM residual plots 47 Figure 2.12: Holcus lanatus GAM residual plots 47 Figure 3.1: Location of field sites 52 Figure 3.2: Contour map derived from Hambledon Hill DEM 55 Figure 3.3: Contour map derived from Sylvan Dale DEM 56 Figure 3.4: False shading image of Hambledon Hill DEM 58 Figure 3.5: False shading image of Sylvan Dale DEM 59 Figure 3.6: Contour map of Sylvan dale showing data loggers 63 Figure 3.7: Contour map of Hambledon Hill showing data loggers 64 Figure 3.8: Mean monthly screen height air temperature at field sites 65 Figure 3.9: Total monthly rainfall at field sites 66 Figure 3.10: Mean monthly relative humidity at field sites 67 Figure 3.11: Monthly mean hourly solar insolation at field sites 67 Figure 3.12: Monthly mean wind speed at field sites 68 Figure 3.13: Daily mean soil moisture (0-5 cm depth) at field sites 69 Figure 3.14: Hourly mean temperatures 25/06/01 at Hambledon AWS 70 Figure 3.15: Hourly mean solar radiation 25/06/01 70 Figure 3.16: Daily minimum screen temperature measured at Hambledon AWS and Fontmell Magna Met Office station during 2001 71 Figure 3.17: Daily maximum screen temperature measured at Hambledon AWS and Fontmell Magna Met Office station during 2001 72 Figure 3.18: Hourly sward temperature measured at Sylvan Dale 73 viii Figure 3.19: Hourly mean climatic data measured at datalogger sites 74 Figure 3.20: Soil temperature under short turf and tussock (green) 75 Figure 3.21: Soil temperature at different altitudes, Hambledon Hill 76 Figure 3.22: Soil temperature at different altitudes, Hambledon Hill 77 Figure 3.23: Soil moisture at (a) Hambledon Hill (b) Sylvan Dale 78 Figure 4.1: Hourly mean modelled and measured solar radiation 85 Figure 4.2: Hourly mean global solar radiation vs PAR 88 Figure 4.3: Hourly mean global solar radiation vs net radiation 88 Figure 4.4: Model of radiation on slopes 91 Figure 4.5: Hourly mean temperatures at Hambledon Hill AWS, 2001 93 Figure 4.6: Values of WpCp plotted against mid-point windspeed 97 Figure 4.7: Model of sward and soil temperature on slopes 100 Figure 4.9: Modelled and measured solar radiation on slopes 106 Figure 4.10: Modelled and measured sward temperature.