A plant ecological evaluation of mechanical bush thinning in Marakele Park, Limpopo Province By FRANCINA CHRISTINA PIENAAR Submitted in fulfilment of the requirements for the degree MAGISTER SCIENTIAE In the faculty of Natural & Agricultural Sciences Department of Animal, Wildlife and Grassland Sciences University of the Free State Bloemfontein South Africa Supervisor: Prof. G.N. Smit Department of Animal, Wildlife and Grassland Sciences, UVS, Bloemfontein Co-supervisor: Dr. P.J. du Preez Department of Plant Sciences, UVS, Bloemfontein May 2006 i ACKNOWLEDGEMENTS I wish to thank the following persons, without whom the execution of this study would not have been possible: My Lord, Jesus Christ, who gave me the strength, ability and insight to complete this study and for the opportunity to experience His glorious creations and to live the life I love. My parents, Willie and Lorraine, for giving me the opportunity to make my dreams a reality, amidst difficult times, and my brother, sister and grandparents for all their support, unconditional love and guidance during this study. My mentor and supervisor, Prof. Nico Smit, for all his guidance, dedication and especially for all his patience and willingness to help amidst a full programme. Your support, perseverance and guidance are sincerely appreciated. My co-supervisor, Dr. Johann Du Preez, for always sharing his expert knowledge and for all his patience throughout this study. The National Research Foundation (NRF) for their financial support during the study period. Mr. Bradley Schroder {Park manager – Marakele Park (Pty.) Ltd.} and his staff for all their cooperation and help during the study period. All the staff of the Department of Animal, Wildlife and Grassland Sciences, especially Prof. Hennie Snyman and Mrs. Linda Nel, for all their support and encouragement throughout the study. Gideon Van Rensburg, I.B. Oosthuizen, Minette and Carissa for all their help during the practical surveys. Mr. Mike Fair for all his assistance during the statistical analyses, and Prof. Chris Du Preez, Dr. Piet Le Roux and Mrs. Yvonne Dessels for all their knowledge and help regarding the soil analyses that was necessary for this study. My special friends, Maré, Michelle, Marsha, CP and especially Samantha for all their encouragement and understanding and for being there through all the ups-and-downs. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS i LIST OF FIGURES vii LIST OF TABLES xii LIST OF APPENDIXES xviii CHAPTER 1: INTRODUCTION 1 CHAPTER 2: STUDY AREA AND TRIAL LAYOUT 7 2.1 STUDY AREA 7 2.1.1 Geographical location 7 2.1.2 History of the Greater Marakele National Park 8 2.1.3 Geology and soil 9 2.1.4 Climate 11 2.1.4.1 Temperature 11 2.1.4.2 Rainfall 13 2.1.5 Vegetation 14 2.1.5.1 The Greater Marakele National Park 14 2.1.5.2 Marakele Park 15 2.1.6 Fauna 18 2.2 TRAIL LAYOUT 19 2.2.1 Method of thinning woody plants 19 2.2.2 Selection of experimental plots 20 2.2.3 Vegetation description of the experimental plots 21 2.2.4 Geology and soil 24 2.2.5 Rainfall and temperature during the study period 24 2.3 TERMINOLOGY 26 CHAPTER 3: PHYTOSOCIOLOGICAL STUDY 27 3.1 INTRODUCTION 27 3.2 PROCEDURE 29 3.2.1 Botanical surveys (analytic phase) 29 3.2.2 Data analyses (synthetic phase) 30 iii 3.3 RESULTS AND DISCUSSION 31 3.3.1 Classification 31 3.3.2 Description of the plant communities 32 3.3.3 Ordination 44 3.4 CONCLUSIONS 46 CHAPTER 4: THE INFLUENCE OF THE TREE THINNING TREATMENTS 48 ON THE DYNAMICS OF THE WOODY LAYER 4.1 INTRODUCTION 48 4.2 PROCEDURE 50 4.2.1 Canopy cover 50 4.2.2 Quantification of the woody layer using the BECVOL-model 51 4.2.3 Data analyses 52 4.3 RESULTS 53 4.3.1 Canopy cover 53 4.3.2 Evapotranspiration Tree Equivalents and tree density 53 4.3.3 Number of stems 65 4.3.4 Leaf dry matter yield 69 4.3.5 Browsing capacity 69 4.4 DISCUSSION 78 4.5 CONCLUSIONS 83 CHAPTER 5: THE INFLUENCE OF THE TREE THINNING TREATMENTS 86 ON THE HERBACEOUS SPECIES COMPOSITION AND VELD CONDITION 5.1 INTRODUCTION 86 5.2 PROCEDURE 88 5.2.1 Quantification of the woody layer 88 5.2.2 Species composition of the herbaceous layer 88 5.2.3 Veld condition assessment 88 5.2.4 Data analyses 89 5.3 RESULTS 90 5.3.1 Quantification of the woody layer 90 5.3.2 Herbaceous species composition 90 iv 5.3.2.1 Acacia mellifera – Grewia flava plots 90 5.3.2.2 Combretum apiculatum – Grewia flava plots 95 5.3.2.3 Acacia erubescens – Dichrostachys cinerea plots 101 5.3.3 Relations between tree leaf biomass and herbaceous species 106 composition 5.3.4 Veld condition assessment 107 5.3.4.1 Ecological grouping 107 5.3.4.2 Veld condition score 115 5.4 DISCUSSION 118 5.5 CONCLUSIONS 126 CHAPTER 6: THE INFLUENCE OF THE TREE THINNING TREATMENT ON 128 THE HERBACEOUS DRY MATTER YIELD 6.1 INTRODUCTION 128 6.2 PROCEDURE 129 6.2.1 Quantification of the woody layer 129 6.2.2 Quantification of the herbaceous layer 130 6.2.3 Calculation of the grazing capacity 132 6.2.4 Data analyses 133 6.3 RESULTS 133 6.3.1 Quantification of the woody layer 133 6.3.2 Quantification of the herbaceous layer 134 6.3.2.1 Total dry matter yield 134 6.3.2.2 Influence of subhabitat differentiation 136 6.3.2.3 Individual species contribution 140 6.3.3 Relations between tree leaf biomass and herbaceous dry matter yield 157 6.3.4 Grazing capacity 161 6.4 DISCUSSION 162 6.5 CONCLUSIONS 169 CHAPTER 7: THE INFLUENCE OF THE TREE THINNING TREATMENTS ON 171 THE PHYSICAL PROPERTIES OF SOIL 7.1 INTRODUCTION 171 7.2 PROCEDURE 172 7.2.1 Soil sampling 172 v 7.2.2 Soil analyses 172 7.2.3 Data analyses 173 7.3 RESULTS 174 7.3.1 Cation concentrations 174 7.3.1.1 Calcium (Ca) 174 7.3.1.2 Potassium (K) 174 7.3.1.3 Magnesium (Mg) 174 7.3.1.4 Sodium (Na) 174 7.3.1.5 Cation Ratios 176 7.3.1.6 Cation Exchange Capacity (CEC), Exchangeable Sodium 176 Percentage (ESP) and Ex changeable Potassium Percentage (EPP) 7.3.2 Soil pH 178 7.3.3 Electrical conductivity and Electrical resistance 180 7.3.4 Sodium Adsorption Ratio (SAR) 181 7.3.5 Nitrogen (N), Organic carbon (C) and Carbon:Nitrogen ratio 182 7.3.6 Phosphorus (P) 184 7.3.7 Soil texture 184 7.4 DISCUSSION 186 7.4.1 Cation concentrations 186 7.4.2 Cation ratios 188 7.4.3 Cation Exchange Capacity (CEC), Exchangeable Sodium 189 Percentage (ESP) and Exchangeable Potassium Percentage (EPP) 7.4.4 Soil pH 191 7.4.5 Electrical conductivity and Electrical resistance 193 7.4.6 Sodium Adsorption Ratio (SAR) 195 7.4.7 Nitrogen (N), Organic carbon (C) and Carbon:Nitrogen ratio 196 7.4.8 Phosphorus (P) 198 7.4.9 Soil texture 199 7.4.10 The influence of variable soil properties on soil water 201 7.5 CONCLUSIONS 203 CHAPTER 8: GENERAL CONCLUSIONS AND RECOMMENDATIONS 205 8.1 INTRODUCTION 205 8.2 GENERAL CONCLUSIONS 205 vi 8.3 RECOMMENDATIONS 206 ABSTRACT 211 OPSOMMING 213 REFERENCES 216 APPENDIX 238 vii LIST OF FIGURES Figure 2.1: An illustration of the conservation areas that is included in the Greater 7 Marakele National Park – namely Marakele National Park, Marakele Park (Pty.) Ltd. (contract park) and Welgevonden private nature reserve. Figure 2.2: The geographical location of the Greater Marakele National Park in 8 relation to the nearest towns and cities. Figure 2.3: The distribution of the different land types and soil forms that can be 10 found in the Greater Marakele National Park (Beech & Van Riet, 2002a). Figure 2.4: Distribution of the different vegetation types, according to Acocks 14 (1988), which can be found in the Greater Marakele National Park. Figure 2.5: An illustration of the different vegetation units that can be found in the 18 Greater Marakele National Park (Beech &Van Riet, 2002b). Figure 2.6: (a) The mechanical mulcher, Barko Tractor, used in Marakele Park for 19 bush encroachment control. (b) The cutter head of the Barko Tractor (cutting width – 2.5 m). Figure 2.7: Photos illustrating what the Acacia mellifera – Grewia flava vegetation 21 unit looked like during the study period. (a) The Acacia mellifera – Grewia flava Treatment plot and (b) the Acacia mellifera – Grewia flava Control plot. Figure 2.8: Photos illustrating what the Combretum apiculatum – Grewia flava 22 vegetation unit looked like during the study period. (a) The Combretum apiculatum – Grewia flava Treatment plot and (b) the Combretum apiculatum – Grewia flava Control plot. Figure 2.9: Photos illustrating what the Acacia erubescens – Dichrostachys cinerea 23 vegetation unit looked like during the study period. (a) The Acacia erubescens – Dichrostachys cinerea Treatment plot and (b) the Acacia erubescens – Dichrostachys cinerea Control. Figure 2.10: Photos illustrating what the Combretum apiculatum – Grewia flava 24 Coppice plot looked like during the study period. Figure 2.11: Photos illustrating what the Acacia mellifera – Grewia flava Coppice 24 plot looked like during the study period. Figure 2.12: Monthly rainfall (mm) recorded in Marakele Park during the study 25 period {July 2003 – June 2004 (first season) and July 2004 – June 2005 (second season)}. Figure 2.13: Seasonal rainfall (mm) for Marakele Park from July 2000 to June 2005.