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Effects of Bush Encroachment Control in a Communal Managed Area in the Taung Region, North West Province, South Africa

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Effects of Bush Encroachment Control in a Communal Managed Area in the Taung Region, North West Province, South Africa Effects of bush encroachment control in a communal managed area in the Taung region, North West Province, South Africa RO Mokgosi orcid.org 0000-0001-8975-0868 Dissertation submitted in fulfilment of the requirements for the degree Magister Scientiae in Botany at the North West University Supervisor: Prof K Kellner Co-supervisor: Prof P Malan Graduation May 2018 21003149 i DECLARATION I, Reamogetswe Olebogeng Mokgosi (21003149), hereby declare that the dissertation titled: Effects of bush encroachment control in a communal managed area in the Taung region, North West Province, South Africa, is my own work and that it has not previously been submitted for a degree qualification to another university. Signature: ……………………………… Date: …………………………. Reamogetswe O. Mokgosi This thesis has been submitted with my approval as a university supervisor and I certify that the requirements for the applicable M.Sc degree rules and regulations have been fulfilled. Signed: ………………………………… Prof. K. Kellner (Supervisor) Date: ……………………....................... Signed: ………………………………. Prof. P.W. Malan (Co-Supervisor) Date: ………………………………….. ii Abstract The communally managed Taung rangelands are degraded because of bush encroachment. Bush encroachment is defined as a natural continuous retrogressive ecological succession, resulting in the increase of both alien and indigenous encroacher woody species and a reduction in grass species composition. This in turn result to changes in soil chemical and physical properties. The knowledge of the interaction between bush encroachment, land-use and soil conditions is essential to sustainably manage these areas. More than 80 % of the respondents in the Taung area owns cattle. To mitigate poverty stress; many pastoralists in the Taung area resorted to high stocking rates, leading to high grazing pressures locally and thereby, led to bush encroachment. The Working for Water (WfW) programme identified the need to implement both mechanical and chemical bush control strategies within the Taung area. Eight study sites were selected for this study. Each of the selected sites had a control and an uncontrolled (benchmark) site. The prominent woody encroacher species within these rangelands were Senegalia mellifera, Vachellia tortilis, V. karroo and Tarchonanthus camphoratus. This posed a threat towards the water resources in Taung communal communities and their economic status.Soil samples were collected and analysed for soil chemical properties such as soil pH, carbon (C) and nitrogen (N) concentrations, C: N ratio, soil magnesium (Mg) and exchangeable magnesium content (Mg2+), soil phosphorus (P) and sodium (Na) concentrations, soil calcium (Ca) content, soil exchangeable (Ca2+) concentration, soil CEC and EC values and the percentage base saturation. The results revealed that, soil pH and carbon concentrations were slightly higher in the uncontrolled sites as compared to the controlled sites. Soil Ca2+, Mg2+ and K concentrations and CEC values were higher in controlled sites as compared to the uncontrolled sites. P concentration, N availability and C: N ratios were limited in both the controlled and uncontrolled sites. EC values varied between the controlledand uncontrolled sites. Keywords: Bush encroachment, carbon and nitrogen concentrations, electrical conductivity (EC), Magnesium (Mg), overgrazing, soil pH, soil chemical properties, Taung communal area. i Acknowledgements I, Reamogetswe Olebogeng Mokgosi, would like to thank the following people and institutions for their assistance and contributions. Firstly, I would like to acknowledge God the All Mighty, for giving me the strength and courage to complete this study. My supervisors, Professor K. Kellner & Professor P.W. Malan, for their assistance, support, guidance and patience to facilitate the success and completion of this study. My mother, S.R. Ramakaba& the Mokgosi family, for their patience, support and encouragement during the course of this study. A special appreciation to my late father, P.J.R. Mokgosi, grandparents, Mr K.T. Mokgosi & Mrs D.G. Mokgosi &also my sister T.E. Sejake, you will always have a special place in my life. My pastor, Apostle M.R. Hanabe &his wife B. Hanabe, for praying with me and encouraging me to complete this study. The Department of Environmental Affairs&the Working for Water programme, for allowing me to conduct this study and also funding this project. I would also like to thank all the people who accompanied me during field surveys and data collection, Mr. Christiaan Harmse, Mr. Albie Götze, Mr. Sampie Van Rooyen, Mrs. Pulane Itumeleng & Ms. Lerato Garekoe. The cooperation and assistance of residents in the Taung community, for assisting me with the completion of social surveys. Mrs Tanya Seiderer, for helping me with the editing of my work. ii List of Contents Abstract …………………………………………………………………………………. i Acknowledgements …………………………………………………………………….. ii List of Figures ………………………………………………………………………….. ix List of Tables …………………………………………………………………………... xii Glossary of Abbreviations …………………………………………………………… xiii CHAPTER 1: INTRODUCTION ...................................................................................... 1 1.1 Background of the study .......................................................................................................... 1 1.2 Importance of ecological restoration in savanna rangelands .............................................. 4 1.3 Rangeland restoration types .................................................................................................... 5 1.3.1 Passive restoration ........................................................................................................ 5 1.3.2 Active restoration ......................................................................................................... 6 1.4 Restoration techniques ............................................................................................................. 6 1.4.1 Re-vegetation of degraded rangelands ......................................................................... 6 1.4.2 Prescribed fire .............................................................................................................. 7 1.4.3 Bush encroachment control .......................................................................................... 8 1.4.4 Rangeland enclosures ................................................................................................... 9 1.4.5 Grazing management ................................................................................................. 10 1.5 The cost of woody plant encroachment in South Africa ................................................... 11 1.6 Working for Water (WfW) programme in South Africa ................................................... 11 1.6.1 The establishment of the WfW programme ............................................................... 11 1.6.2 The significance of the Working for Water (WfW) programme ............................... 12 1.7 Problem statement of this study ............................................................................................ 14 1.8 Aim of the study ..................................................................................................................... 15 1.9 Framework ............................................................................................................................... 16 CHAPTER 2: LITERATURE REVIEW ........................................................................ 18 2.1 The savanna rangelands and the problem of bush encroachment .................................... 18 2.2 The economic significance of African savannas ................................................................ 20 iii 2.3 Effects of bush encroachment ............................................................................................... 22 2.3.1 Grazing ....................................................................................................................... 22 2.3.2 Soil conditions (or properties) as a result of bush encroachment .............................. 23 2.3.3 Rainfall variability ..................................................................................................... 25 2.3.4 Fire management ........................................................................................................ 27 2.3.5 Climate change ........................................................................................................... 28 2.3.6 Increased CO2 levels .................................................................................................. 28 2.4 Walter’s (1939) two-layer hypothesis .................................................................................. 30 2.4.1 Positive effects of trees on grasses ............................................................................. 31 2.4.2 Negative effects of trees on grasses ........................................................................... 32 2.5 Bush encroachment in communal rangelands of South Africa ........................................ 33 2.6 The involvement of indigenous knowledge towards bush encroachment ...................... 35 2.7 Bush control methods ............................................................................................................. 36 2.7.1 Mechanical control ..................................................................................................... 39 2.7.3 Chemical control .......................................................................................................
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