Aspects of the Structure and Functioning of the Vegetation of the Hlatikulu Vlei
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ASPECTS OF THE STRUCTURE AND FUNCTIONING OF THE VEGETATION OF THE HLATIKULU VLEI by lAIN ANDREW GUTHRIE Submitted in fulfilment of the academic requirements for the degree of: MASTER OF SCIENCE in the Department of Botany University of Natal Pietermaritzburg 1996 DECLARATION . These studies represent original work by the author and have not otherwise been submitted in any form for any degree or diploma to any University. Where use has been made of the work of others it is duly acknowledged in the text. LA. Guthrie ACKNOWLEDGEMENTS I should like to express my sincere thanks and appreciation to the following people and organisations for their various inputs into this project: To my supervisor, Dr J.E. Granger, for initiating the project and for his advice and help. Professor van J. Staaden for making facilities at the Department of Botany available to me during various stages of the project. The South African Crane Foundation and Mondi Ltd. for the opportunity to work at the Hlatikulu Crane and Wetland Sanctuary, and the various landowners at Hlatikulu Vlei: Mr P.M. Theron, Mrs du Preez, Mr Harburn, Mrs Hobson and Messrs Steyn, for permission to conduct research on their land. To the NU-NPB Fund, the Foundation for Research Development and the University of Natal for financial support. Henry and Sue Davies for their help, encouragement and support throughout the project. Henry Davies initially proposed the project and did much to facilitate its smooth working at Hlatikulu Vlei. Mary Livingstone for providing a base and a home for the many months spent at the vlei during the field work. Ian Peddie and the late Paul Burke for assistance with the field work at the vlei. Prof K.D. Gordon-Gray and Jane Browning for help with the identification of sedges and grasses from the vlei. 1 Jane Browning for her constant support, encouragement and advice throughout the project. Dr Trevor Edwards for help with the identification of various species from the vlei. Shell S.A. for their donation of nine 200 litre drums for use in the flooding experiment. To Jenny Mander and Fonda Lewis at the Institute for Natural Resources for aid in digiti sing the vegetation maps. To the staff at the Computer Centre for Water Research for help in obtaining simulated rainfall data for Hlatikulu Vlei, Ntabamhlope Vlei and the mires at Highmoor. To Koen Albertyn of the Natal Parks Board at Highmoor for help and advice in the location of sites at the mires at Highmoor. Dr M.A. Johnston, Department of Soil Sciences, University of Natal, for help with soil moisture retentivity and the use of facilities in the Agronomy Department. To my parents, family and friends for their continued support and encouragement throughout the project. Finally to my wife Emma, who has been a constant support through the entire project, not only by helping set up various experiments and collecting of data during the field work, but also in the production, correction and vetting of the various drafts and final compilation of this thesis. 11 ABSTRACT Hlatikulu Vlei, situated in the foothills of the Natal Drakensberg, is one of the priority wetlands in KwaZulu-Natal, occupying an area of 733 Hectares. The importance of Hlatikulu Vlei lies in its functions to store water, regulate stream flow and attenuate floods, as well as to provide suitable habitat for wildlife and grazing for livestock. Hlatikulu Vlei is a threatened system and has suffered the effects of human mismanagement. Forty-nine percent of the vlei has been classified as disturbed or destroyed, mainly due to the construction of two large dams and past drainage of vlei to facilitate pasture planting. The effects of grazing and fire on the plant communities has been considerably less. Vegetation communities at Hlatikulu Vlei have similarities with those at Ntabamhlope Vlei. The main plant communities present at Hlatikulu Vlei are: vlei grassland, sege meadows, bulrushes and reedswamp. Species compositions of the mixed sedge and grass sedge-meadow community have a notably higher species diversity than similar communities sampled at Ntabamhlope Vlei and the mires at Higbmoor. Soil type and moisture content are shown to be the most significant environmental factors determining the distribution of plant communities and species within the vlei. A wetland re-establishment and rehabilitation programme in the Hlatikulu Crane and Wetland Sanctuary has been effective in allowing many wetland plants to become re established. The sanctuary communities bear greater similarity to the sedge and rush sedge-meadow community, than the mixed sedge and grass sedge-meadow communities that were originally present. This is also reflected in the seed bank. All three Southern African crane species (Blue, Wattled and Crowned Crane) and fourteen species of waterfowl have been recorded in the Hlatikulu Crane and Wetland Sanctuary since the wetland rehabilitation programme. The waterfowl playa role in the dispersal of seeds into the sanctuary, particularly those of Schoenoplectus decipiens and HI Eleocharis dregeana and are in part responsible for the return of certain wetland plants to the sanctuary. The flooding of soils, the fluctuating water level and the soil type related to hummocks and to channels are shown to be responsible for the location of Cyperus denudatus , Arundinella nepalensis and Aristida junciformis in differing positions in the channels and on the hummocks and are also responsible for the maintenance and functioning of the hummocks and channels. Seed banks on the hummocks are similar to seed banks in the channels, however the extant vegetation on the hummocks is distinctly different to that in the channels. Certain species represented in the channel seed bank are being excluded from surviving to maturity. IV CONTENTS ACKNOWLEDGEMENTS ABSTRACT 111 T ABLE OF CONTENTS v CHAPTER 1: INTRODUCTION 1 CHAPTER 2: OBJECTIVES OF STUDY 11 CHAPTER 3: STUDY AREA 14 3.1 Introduction 14 3.2 Defmition of wetlands 14 3.3 Location 16 3.4 Geology 19 3.5 Soils 19 3.6 Topography 20 3.7 Hydrology 20 3.8 Climate 21 3.9 Fauna and Flora 24 3.10 History of the Area 29 CHAPTER 4: CLASSIFICATION AND COMPARISON OF WETLAND VEGETATION AT HLATIKULU VLEI, NT ABAMHLOPE VLEI AND HIGHMOOR WETLANDS. 32 4.1 Introduction 32 4.2 Study areas 34 4.3 Methods 34 4.3. 1 Sample site location 34 v 4.3.2 Sampling 35 4.3.3 Environmental factors 36 4.4 Data entry 38 4.5 Vegetation Analysis 39 4.5.1 Classification 39 4.5.1.1 Two-Way Indicator Species Analysis (TWINSPAN) 39 4.6 Sequence of analysis 40 4.7 Results 40 4.7.1 Classification and description of vegetation communities at Hlatikulu Vlei 48 4.7.2 Classification and description of vegetation communities at Ntabamhlope Vlei 55 4.7.3 Classification and description of vegetation communities at the mires at Highmoor 60 4.8 Discussion of results and comparisons of the vegetation communities at Hlatikulu Vlei, Ntabamhlope Vlei and the mires at Highmoor 64 4.9 Conclusion 74 CHAPTER 5: VEGETATION MAPPING 76 5.1 Introduction 76 5.2 Study Area 77 5.3 Methods 77 5.4 Definition of plant communities in vegetation maps 79 5.5 Results 81 5.6 Discussion 88 5.7 Conclusion 90 CHAPTER 6: THE RELATIONSHIP BElWEEN SPECIES AND CERTAIN ENVIRONMENTAL VARIABLES IN THE VEGETATION COMMUNITIES OF HLATIKULU VLEI 92 6.1 Introduction 92 vi 6.2 Methods 94 6.2.1 Sample site location 94 6.2.2 Environmental factors 94 6.2.3 Sampling 96 6.3 Data entry 96 6.4 Results 96 6.5 Discussion 105 6.6 Conclusion 110 CHAPTER 7: EFFECTS OF A WETLAND RE-ESTABLISHMENT AND REHABILITATION PROGRAMME ON THE VEGETATION AND SEED BANK DYNAMICS IN THE HLATIKULU CRANE AND WETLAND SANCTUARY 7. 1 Introduction 112 7.2. Methods 117 7.2.1 Vegetation sampling in the Hlatikulu Crane and Wetland Sanctuary 117 7.2.1.1 Vegetation prior to draining of sanctuary 117 7.2.1.2 Vegetation prior to the wetland re-establishment and rehabilitation programme 117 7.2. 1.3 Extant vegetation in the sanctuary 118 7.2.2 Soil stored seed bank sampling 123 7.2.2. 1 Seed bank prior to draining of sanctuary 124 7.2.2.2 Seed bank prior to the wetland re-establishment and rehabilitation programme 125 7.2.2.3 Extant seed banks in the sanctuary 125 7.3 Results 127 7.3.1 Vegetation sampling in the Hlatikulu Crane and Wetland Sanctuary 127 7.3. 1.1 Vegetation prior to draining of sanctuary 127 Vll 7.3. 1.2 Vegetation prior to the wetland re-establishment and rehabilitation programme 127 7.3.1 .3 Extant vegetation in the sanctuary 131 7.3.1.3.1 Ordination of species in extant vegetation in the sanctuary 136 7.3 .2 Soil stored seed bank sampling 140 7.3.2.1 Seed bank prior to draining of sanctuary 140 7.3.2.2 Seed bank prior to the wetland re-establishment and rehabilitation progranune 142 7.3.2.3 Extant seed banks in the sanctuary 142 7.4 Discussion 144 7.5 Conclusion 148 CHAPTER 8: USE OF THE HLATIKULU CRANE AND WETLAND SANCTUARY BY CRANES AND WATERFOWL AND THEIR ROLE IN THE DISPERSAL OF PLANT PROPAGULES 8.1 Introduction 150 8.2. Methods 152 8.2.1 Censii of crane and waterfowl 152 8.2.2 Role of waterfowl in the dispersal of plant propagules 152 8.3 Results 153 8.3.1 Censii of cranes and waterfowl 153 8.3 .2 Role of waterfowl in the dispersal of plant propagules 154 8.4 Discussion 154 8.5 Conclusion 158 VIll CHAPTER 9: ASPECTS OF THE FORMATION, MAINTENANCE AND FUNCTIONING OF HUMMOCKS AND CHANNELS AT HLATIKULU VLEI 9.1 Introduction 159 9.2 Methods 161 9.2.1 Flooding and fluctuation of water levels 161 9.2.1.1 Soil 161 9.2.1.2 Plant species selected 163 9.2.1.3 F ire treatment 163 9.2.1.4 Flooding 165 9.2.1.5 Fluctuating water levels 165 9.2.1.6 Data collection and analysis 167 9.2.2 Soil stored seed bank sampling 167 9.3 Results 168 9.3.1 Flooding experiment 168 9.3.2 Seed banks 172 9.4 Discussion 172 9.4 Conclusion 174 CHAPTER 10: CONCLUSIONS 176 REFERENCES 180 APPENDICES 191 IX 1 CHAPTER 1 INTRODUCTION 'Wetlands are among the most important ecosystems on the Earth' Mitsch & Gosselink:, 1986 On the second of February 1971 the Ramsar Convention on 'Wetlands of International Importance especially as Waterfowl Habitat' was signed in Iran.