A modelling approach to farm management and vegetation degradation in pre-modern Iceland By Amanda Mary Thomson Submitted to The Faculty of Natural Sciences, University of Stirling, March 2003 For the degree of Doctor of Philosophy This research was undertaken at the Department of Environmental Science, University of Stirling, Stirling, UK. Statement of originality I hereby confirm that this is an original study conducted independently by the undersigned and the work contained herein has not been submitted for any other degree. All research material has been duly acknowledged and cited. Signature of candidate: Date: TABLE OF CONTENTS TABLE OF CONTENTS……………………………………………………………..i LIST OF FIGURES………………………………………………………………...viii LIST OF TABLES……………………………………………………………….....xvi ACKNOWLEDGEMENTS………………………………………………………..xix ABSTRACT……………………………………………………………………….…xx GLOSSARY OF ABBREVIATIONS AND ICELANDIC TERMS………….…xxi CHAPTER 1: INTRODUCTION AND AIMS: LANDSCAPE MODIFICATION BY GRAZING ......................................................................................................... 1 1.1 INTRODUCTION ................................................................................................. 1 1.2 THE HUMAN ROLE IN OVER-GRAZING ................................................................. 2 1.3 ICELAND: A LANDSCAPE MODIFIED BY GRAZING ................................................. 3 1.3.1 Physical environment of Iceland................................................................. 4 1.3.1.1 The climate of Iceland.......................................................................... 4 1.3.1.2 The geology and soils of Iceland ........................................................ 11 1.3.1.3 Vegetation cover and history.............................................................. 14 1.3.2 Resource management and the pre-modern agricultural system ................ 16 1.3.3 Indications of land degradation in Iceland ................................................ 21 1.4 THE IMMEDIATE CAUSES AND PROCESS OF DEGRADATION................................. 24 1.5 ALTERNATIVE EXPLANATIONS OF LAND DEGRADATION IN ICELAND.................. 31 1.6 RESEARCH INTO THE ANTHROPOGENIC INFLUENCE ON LAND DEGRADATION IN ICELAND............................................................................................................... 36 1.6.1 The ‘Tragedy of the Commons’................................................................ 38 1.6.2 The impact of the first settlers .................................................................. 40 i 1.6.3 An historical ecology perspective ............................................................. 43 1.6.4 Summary of anthropogenic impacts.......................................................... 45 1.7 THE AIMS AND HYPOTHESES OF THE RESEARCH PROJECT................................... 47 CHAPTER 2: RESEARCH DESIGN AND METHODOLOGY......................... 49 2.1 INTRODUCTION ............................................................................................... 49 2.2 THE POTENTIAL FOR MODELLING ..................................................................... 50 2.3 THE CASE FOR A SPECIFIC ICELANDIC GRAZING MODEL..................................... 51 2.4 THE DEVELOPMENT OF BÚMODEL .................................................................... 53 2.5 MODEL SIMULATION RUNS .............................................................................. 58 2.6 CASE STUDY REGION I: VESTUR-EYJAFJALLAHREPPUR .................................... 61 2.7 CASE STUDY REGION II: MÝVATN HREPPUR ..................................................... 70 2.8 SUMMARY ...................................................................................................... 80 CHAPTER 3: THE CONSTRUCTION OF THE GRAZING SIMULATION MODEL I: INPUTS .............................................................................................. 85 3.1 INTRODUCTION ............................................................................................... 85 3.2 LANDSCAPE/ENVIRONMENTAL INPUTS ............................................................. 88 3.2.1 The vegetation classification .................................................................... 88 3.2.1.1 Vegetation community classifications in the literature........................ 89 3.2.1.2 Original fieldwork: botanical composition.......................................... 92 Fieldwork in 2000 ...................................................................................... 93 2000 fieldwork methodology...................................................................... 93 Fieldwork in 2001 ...................................................................................... 94 3.2.1.3 Búmodel vegetation classification ...................................................... 99 3.2.2 Land use categories .................................................................................105 ii 3.2.2.1 The tún zone of activity.....................................................................105 3.2.2.2 The outfield zone of activity..............................................................105 3.2.2.3 The rangeland zone of activity...........................................................107 3.2.3 Climate scenarios ....................................................................................107 3.2.3.1 The baseline scenario I......................................................................109 3.2.3.2 The extremely cold scenario II (1859 to 1868 type)...........................110 3.2.3.3 The cold scenario III (average of 10 coldest years 1937 - 1995) ........112 3.2.3.4 The warm scenario IV (average of 10 warmest years 1937 - 1995)....112 3.3 LIVESTOCK INPUTS.........................................................................................112 3.3.1 Flock size and composition .....................................................................113 3.3.2 Livestock body weight ............................................................................114 CHAPTER 4: THE CONSTRUCTION OF THE GRAZING MODEL II: PROCESSES AND OUTPUTS............................................................................116 4.1 MAINTENANCE FEED REQUIREMENTS SUB-MODEL ...........................................116 4.1.1 Calculation of maintenance requirements for adult sheep.........................118 4.1.2 Calculation of fodder requirements for lamb growth................................119 4.1.3 Grazing conditions ..................................................................................120 4.2 VEGETATION PALATABILITY AND PLANT PREFERENCES SUB-MODEL.................121 4.2.1 Components of vegetation palatability.....................................................123 4.2.2 Seasonal variation in vegetation palatability ............................................125 4.2.3 Construction of the plant preferences sub-model .....................................128 4.3 THE UTILISABLE BIOMASS SUB-MODEL............................................................131 4.3.1 Utilisable biomass and growing season....................................................131 4.3.2 A review of utilisable biomass measurements in the literature .................134 4.3.2.1 The RALA grazing research programme ...........................................136 iii 4.3.2.2 The horse grazing pasture project......................................................139 4.3.3 Original fieldwork: utilisable biomass .....................................................143 Statistical analysis of utilisable biomass samples .......................................144 4.3.4 The impact of climate upon utilisable biomass.........................................146 4.3.5 Intra-annual change in utilisable biomass ................................................151 4.3.6 Formulation of growth curves for Búmodel .............................................153 4.4 LIVESTOCK DISTRIBUTION SUB-MODEL ...........................................................156 4.5 OFFTAKE SUB-MODEL.....................................................................................163 4.6 GRAZING INTENSITY AND THE BIOMASS PRODUCTION FEEDBACK LOOP ............163 4.6.1 Grazing utilisation thresholds ..................................................................166 4.6.2 The biomass production-offtake feedback sub-model ..............................167 4.7 HAY MAKING SUB-MODEL ..............................................................................167 4.8 THE MODEL INTERFACE: SPREADSHEETS AND GIS...........................................175 4.9 SUMMARY OF THE MODELLING CHAPTERS .......................................................176 CHAPTER 5: MODEL EVALUATION: SENSITIVITY ANALYSIS AND VALIDATION......................................................................................................181 5.1 INTRODUCTION ..............................................................................................181 5.2 STRUCTURAL VALIDATION OR VERIFICATION OF BÚMODEL..............................182 5.3 SENSITIVITY ANALYSES ..................................................................................182 5.3.1 Livestock numbers ..................................................................................183 5.3.2 Climatic scenarios ...................................................................................193 5.3.3 Livestock distribution..............................................................................193 5.3.4 Lambing rates .........................................................................................197