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Montane Wetlands of the South African Great Escarpment: Plant Communities and Environmental Drivers

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Montane Wetlands of the South African Great Escarpment: Plant Communities and Environmental Drivers Montane Wetlands of the South African Great Escarpment: Plant Communities and Environmental Drivers A thesis submitted in fulfilment of the requirements of the degree of MASTER OF SCIENCE of RHODES UNIVERSITY BY MATTHEW RICHARD JANKS DECEMBER 2014 Supervisor: Prof. N. Barker (Department of Botany, Rhodes University) Co-supervisor: Dr. Erwin Sieben (Department of Plant Science, University of the Free State) Abstract Wetlands provide a number of valuable functions to both the surrounding environment and society. The anaerobic conditions created by flooding in wetlands provide a habitat that supports unique assemblages of plant life. High altitude wetlands are amongst the most species-rich in South Africa. They house a number of rare species and play a vital role in the supply of water to lower lying areas. These are some of the reasons that mountain wetlands are of high conservation value. A phytosociological study was undertaken on the high altitude wetlands of the Great Escarpment with the aim of classifying the plant communities and identifying the environmental drivers of plant community patterns within these ecosystems. Data collection was focused in the Eastern Cape and was supplemented with data from existing studies to gain a more complete understanding of the wetlands of the Great Escarpment of South Africa. Using the Braun-Blanquet approach, Hierarchical Cluster Analysis and Indicator Species Analysis; five broad wetland groups were identified, comprised of 33 individual plant communities and 81 indicator species. Multivariate analysis, including Canonical Correspondence Analysis revealed that the effects of altitude, such as temperature and rainfall, are the most significant large-scale drivers of vegetation patterns. Smaller scale drivers include wetness and soil nutrients including nitrogen, phosphorus, electrical conductivity, sodium, and organic content. The identification of indicator species served to reveal potentially important wetland species across different areas of the Great Escarpment. The effects of altitude on plant community patterns highlights the susceptibility of the high altitude specific communities to upward temperature zone shifts resulting from global warming. Other threats include livestock trampling, water extraction, and land use change for agricultural purposes. The relative absence of alien species in these wetlands gives an indication of their pristine condition and therefore their importance as a reference from which they may be monitored. A large proportion of the wetlands studied here occur outside protected areas, and given the rate of wetland loss in South Africa, it is important that continued effective land management is practiced to ensure that these ecosystems are conserved in the future . II Table of Contents Abstract ................................................................................................................................II Table of Contents ................................................................................................................ III List of Tables ...................................................................................................................... VI List of Figures .................................................................................................................... VII List of Abbreviations........................................................................................................... IX Acknowledgements ............................................................................................................. XI Declaration......................................................................................................................... XII CHAPTER 1 ......................................................................................................................... 1 GENERAL INTRODUCTION.............................................................................................. 1 Wetlands: An Overview..................................................................................................... 1 Wetland Services ............................................................................................................... 2 Hydrological Functions.................................................................................................. 2 Biogeochemical Functions ............................................................................................. 2 Plant and Wildlife Habitat ............................................................................................. 2 Wetland Soils .................................................................................................................... 3 Wetland Plants................................................................................................................... 3 Threats to Wetlands ........................................................................................................... 4 Wetland Conservation ....................................................................................................... 5 Wetlands of South Africa................................................................................................... 5 Mountain Wetlands of South Africa ................................................................................... 8 Rationale ........................................................................................................................... 9 Aims ................................................................................................................................ 10 Thesis Structure ............................................................................................................... 10 CHAPTER 2 ....................................................................................................................... 11 GENERAL MATERIALS AND METHODS ...................................................................... 11 Description of the Study Area .......................................................................................... 11 Vegetation: General Patterns ....................................................................................... 17 Geology and Soils ........................................................................................................ 18 Climate ........................................................................................................................ 18 Methods .......................................................................................................................... 19 Site Selection................................................................................................................ 19 Vegetation Survey ........................................................................................................ 20 III Description of Environmental Variables....................................................................... 21 Incorporation of Data into the National Wetlands Vegetation Database....................... 22 Analysis ....................................................................................................................... 26 CHAPTER 3 ....................................................................................................................... 27 VEGETATION CHARACTERISTICS, COMMUNITY CLASSIFICATION, AND COMMUNITY DESCRIPTION OF THE GREAT ESCARPMENT WETLANDS ............. 27 Introduction ..................................................................................................................... 27 Aims ................................................................................................................................ 28 Materials and Methods .................................................................................................... 28 Plant Community Classification ................................................................................... 28 Results ............................................................................................................................. 29 Wetland Flora and Diversity ........................................................................................ 29 Floristic Affinities ........................................................................................................ 34 Classification ............................................................................................................... 34 Descriptions of the Montane Wetland Plant Communities of the Great Escarpment ......... 41 Merxmuellera macowanii Wetlands ............................................................................. 41 The High Altitude Fen and Seepage Wetlands .............................................................. 43 The Common Escarpment Sedge and Grassy Communities .......................................... 48 The Miscanthus capensis Wetlands .............................................................................. 54 The Eastern Escarpment Wetlands ............................................................................... 55 Conclusion ...................................................................................................................... 57 CHAPTER 4 ....................................................................................................................... 58 Environmental Drivers of Wetland Plant Community Patterns ............................................ 58 Introduction ....................................................................................................................
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