FLOODPLAIN VEGETATION RESPONSES TO FLOOD REGIME IN THE SEASONAL OKAVANGO DELTA, BOTSWANA By MICHAEL MURRAY-HUDSON A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2009 1 ©2009 Michael Murray-Hudson 2 To the late Pete Smith, who planted the seed, and to Frances, who helped it grow. 3 ACKNOWLEDGEMENTS The research on which this dissertation is based was funded and supported by many and various agencies: The University of Botswana, University of Florida (Adaptive Management: Water, Wetlands and Watersheds program funded by the National Science Foundation), and the Biokavango project (Global Environment Facility). The University of Botswana also provided funding for the costs of studying and living abroad. Their support is gratefully acknowledged. In addition the support of all of the staff at the Harry Oppenheimer Okavango Research Centre was instrumental in facilitating both the field research and the remote sensing components of this work. In particular, Piotr Wolski (who can make computers work for him), Cornelis Vanderpost for help with imagery, and Wilfred Kaneguba, Moagisi Diare, Florian Bendsen and Aulter Karumendu for unflagging enthusiasm, willingness to do transects chest deep in crocodile- infested waters, and very fine goat stews in very remote places. Dr Jonathan Timberlake and the staff at the Royal Botanical Gardens in Kew, England, provided invaluable help with identifying stubborn species. Special thanks are due to Dr Mark Brown, my supervisor, for allowing me great flexibility in achieving my goals, and for the field trips in support of the Integrative Graduate Education and Research Traineeship Program (IGERT) program. Thanks are also due to the following hunting and photographic safari operators for their cooperation: Harry Charalambous (Johan Calitz Safaris), Horseback Safaris, Elephant Back Safaris, and Rann Hunting Safaris. Lastly, and most important, my wife Frances not only participated in the field data collection, but also put up with me and my moods throughout the entire process: without her this dissertation would not have been possible. 4 TABLE OF CONTENTS page ACKNOWLEDGEMENTS......................................................................................................... 4 LIST OF TABLES ...................................................................................................................... 7 LIST OF FIGURES .................................................................................................................... 8 ABSTRACT ............................................................................................................................. 10 CHAPTER 1 INTRODUCTION ............................................................................................................. 12 Problem Statement ............................................................................................................. 12 Hydrology and Wetland Vegetation.................................................................................... 12 The Okavango Delta: A Flood-Pulsed Tropical Wetland .................................................... 15 Research Questions ............................................................................................................ 17 Dissertation Structure ......................................................................................................... 18 2 PREDICTING VEGETATION SUCCESSIONAL STAGE IN SEASONAL FLOODPLAINS FROM REMOTE SENSING-DERIVED HYDROLOGICAL HISTORY .......................................................................................................................... 23 Introduction........................................................................................................................ 23 Methods ............................................................................................................................. 27 Establishing Historical Hydroperiod ............................................................................ 27 Establishing Extant Floodplain Vegetation State ......................................................... 28 Results And Discussion ...................................................................................................... 29 Hydrological Variables ................................................................................................ 29 Flood Duration 2000-2007 .......................................................................................... 30 Vegetation-Hydroperiod Relationships ........................................................................ 31 Conclusions........................................................................................................................ 34 3 A VEGETATION-BASED HIERARCHICAL CLASSIFICATION FOR SEASONALLY PULSED FLOODPLAINS IN THE OKAVANGO DELTA .................... 43 Introduction........................................................................................................................ 43 Methods ............................................................................................................................. 46 Results ............................................................................................................................... 48 Discussion .......................................................................................................................... 50 Conclusions........................................................................................................................ 54 4 AN ANNUAL FLOOD PULSE AS THE PRIMARY DRIVER OF PLANT SPECIES DISTRIBUTION IN SEASONAL FLOODPLAINS OF THE OKAVANGO DELTA, BOTSWANA ..................................................................................................................... 62 5 Introduction........................................................................................................................ 62 Methods ............................................................................................................................. 64 Hydrological Variables ................................................................................................ 64 Vegetation Sampling ................................................................................................... 64 Analysis ...................................................................................................................... 65 Results ............................................................................................................................... 67 General Floristics ........................................................................................................ 67 Hydrology ................................................................................................................... 67 Hydrology-Vegetation Relationships ........................................................................... 68 Discussion .......................................................................................................................... 71 Conclusions........................................................................................................................ 76 5 A SPECIES-DISTRIBUTION MODEL FOR INVESTIGATING HYDROLOGICALLY-INDUCED CHANGES IN FLOODPLAIN VEGETATION IN LARGE FLOOD-PULSED TROPICAL WETLANDS. ..................................................... 87 Introduction........................................................................................................................ 87 Methods ............................................................................................................................. 90 Vegetation Species Composition ................................................................................. 90 Hydrological Variables For GLM Development .......................................................... 90 Species Distribution Model Derivation ........................................................................ 91 The Hydrological And Spatial Species Distribution Models ........................................ 92 Scenarios Of Change ................................................................................................... 93 Results ............................................................................................................................... 94 Discussion .......................................................................................................................... 96 Conclusions........................................................................................................................ 99 6 CONCLUSION ................................................................................................................ 109 APPENDIX 1. VEGETATION SURVEY SITE DATA ......................................................... 112 LIST OF REFERENCES ........................................................................................................ 114 BIOGRAPHICAL SKETCH ................................................................................................... 124 6 LIST OF TABLES Table page 2-1 Areas of flood frequency strata used in sample site selection. ........................................ 35 2-2 Comparison of accuracy of different wet-dry classification techniques for Moderate Resolution Imaging Spectroradiometer (MODIS)