PHYTOSOCIOLOGY OF THE NAMIB DESERT PARK, SOUTH WEST AFRICA by Ernest Richard Robinson B.Sc. (Hons.) (Natal) Submitted in partial fulfilment of the requirements for the degree of Master of Science in the Department of Botany University of Natal PIETERMARITZBURG NOVEMBER 1976 I HEREBY DECLARE THAT, EXCEPT WHERE OTHERWISE STATED, ALL MATERIAL PRESENTED HEREUNDER IS ORIGINAL AND HAS NOT PREVIOUSLY BEEN SUB - MITTED FOR PUBLICATION OR ANY OTHER PURPOSE. i TABLE DF CONTENTS. PAGE Acknowledgements. v Summary. vii Chapter 1 Introduction 1 Chapter 2 Methods ...... 5 2.1 Introduction : Why classify the vegetation ? • 5 2.2 Classification of the vegetation ...... 6 2.2.1 Choice of the Braun-Blanquet method 6 2.2.2 Application of the method 7 2.2.2.1 Collection of field data • • 7 2.2.2.2 Synthesis of the data • 13 2.3 Measurement of infiltration rate of water on the plains ................ 14 Chapter 3 The study area 17 3.1 Introduction 17 3.2 Geology 18 3.3 Topography ..... 20 3.3.1 Lagoons and salt marshes 20 3.3.2 The sand dunes 21 3.3.3 The plains north of the Kuiseb River .... 23 3.3.4 Drainage and associated features 23 3.3.5 Pans 25 3.3.6 Inselbergs and rock outcrops ........ 25 3.4 Soils 26 3.4.1 Soils of the dune areas 26 3.4.2 Syrosems 27 3.4.3 Limestone soils • 27 3.4.4 Soils of gypsum crusts 29 3.4.5 Silts and flood-loam soils • • 30 3.4.6 Gravels of the watercourses 30 3.4.7 Saline soils 31 3.5 Conclusion 31 Chapter 4 Climate 32 4.1 Introduction 32 4.1.1 Description of the climate of the Namib Desert 32 4.1.2 Factors responsible for the existence of the 34 desert ii PAGE 4.1.3 The climate of the study area ........ 35 4.2 Cloudiness 36 4.3 Insolation 37 4.4 Temperature ...... 38 4.4.1 Air temperature . 38 4.4.2 Soil temperature 40 4.5 Wind 41 4.6 Sandstorms ..... 42 4.7 Precipitation 43 4.7.1 Kinds of precipitation 43 4.7.2 Rain 43 4.7.3 Fog 45 4.7.4 Hail 48 4.8 Relative humidity 49 4.9 Evaporation 50 Chapter 5 Results and Discussion Introduction . ....... 52 5.1 The salt marsh system . 53 5.1.1 General 53 5.1.2 The salt marsh communities .......... 53 5.1.2.1 The Typha latifolia community . 53 5.1.2.2 The Arthrocnemum affine community 55 5.1.2.3 The Sporobolus virginicus community .... 58 a The typical sub-community 58 b The Scirpus dioicus sub-community 60 c The Phragmites australis sub-community ... 61 5.1.2.4 The Odyssea paucinervis community 63 5.1.3 Discussion of the relationships of the salt marsh communities ...... 64 Floristic relationships . 64 Ecological relationships ..... 65 5.1.4 Syntaxonomic position of the salt marsh communities . ......... 66 5.2 The sand dune system 68 5.2.1 Introduction 68 5.2.2 The sand dune communities 69 5.2.2.1 The Eragrostis cyperoiaes community .... 69 5.2.2.2 The Stipayrostis sabulicola community ... 71 iii PAGE 5.2.2.3 The Acanthosicyos horrida community ..... 72 5.2.2.4 The Stipagrostis gonatostachys community ... 74 5.2.2.5 The S_. lutescens community 76 a The typical sub-community ......... 76 b The Limeum fenestratum - Hermannia gariepina sub-community 78 5.2.3 Discussion of the dune communities ...... 80 5.2.3.1 Floristic relationships . 80 5.2.3.2 Ecological relationships .... 80 5.2.3.3 Syntaxonomic position of the communities ... 81 5.3 Communities of the washes, Kuiseb River and rock outcrops 83 5.3.1 Introduction (i) Reasons for grouping these habitats 83 (ii) Status of the Pechuel-Loeschea leubnitziae and Zygophyllum stapfii communities 83 5.3.2 Communities of the washes, river and outcrops 84 5.3.2.1 The Asclepias buchenaviana community ..... 84 5.3.2.2 The Acacia giraffae community ......... 85 a The typical sub-community 86 b The Acacia albida sub-community ....... 88 5.3.2.3 The Datura spp. - Argemone ochroleuca community 91 5.3.2.4 The Pechuel - Loeschea leubnitziae community 94 5.3.2.5 The Zygophyllum stapfii community 97 5.3.2.6 The Adenolobus pechuelii - Acacia reficiens community ........... 99 5.3.2.7 The Mesembryanthemum guerichianum - Sporobolus nebulosus community ....... 103 • 5.3.2.8 The Petalidium setosum community ....... 105 5.3.2.9 The Sesuvium sesuvioides - Stipagrostis obtusa community ........ 108 5.3.2.10 The Monechma genistifolium community ..... 110 5.3.2.11 The Petalidium variabile community . 113 5.3.3.12 The Commiphora glaucescens - Anthephora pubescens community 116 5.3.3 Relationships between the communities .... 122 iv PAGE 5.4 Communities of the larger pans 122 5.4.1 Introduction 122 5.4.2 The Platycarpha carlinoides community . 122 5.4.3 The Calicorema capitata community . 124 a The Aptosimum spinescens sub-community . 124 b The typical sub-community 125 5.4.4 The Aristida adscencionis - Eragrostis annulata community 127 5.4.5 Relationships between the communities . 131 5.5 Communities of the "Namib fog desert" and the inland plains ........... 132 5.5.1 Introduction 132 5.5.2 Description of the communities 132 5.5.2.1 The Salsola nollothensis community . 132 5.5.2.2 The Salsola tuberculata community . 134 a The typical sub-community 135 b The Zygophyllum stapfii sub-community . 137 c The Arthraerua leubnitziae sub-community 140 d The Stipagrostis obtusa sub-community . 142 5.5.2.3 The Stipagrostis ciliata community . 146 5.6 Discussion of results and notes on inter­ relationships of the communities of the river, washes, pans, plains and rock outcrops . 150 5.6.1 Slope and aspect ............ 150 5.6.2 Environmental gradients 151 5.6.3 Life forms 153 5.6.4 Relationships between the communities . 154 Chapter 6 General discussion and conclusions ri,"i Discussion of results and recommendations for future studies ..... 159 6.2 Conclusions . 163 Literature cited 164 Appendix I List of all species recorded from relev^s . 176 Appendix II Life form class definitions 217 Appendix III Floristic affinities of the communities, measured by S^renson coefficients of similarity ... 218 Maps showing the location of relevfis of the communities . from 221 Phytosociolo^ical tables (Tables I to VII) . In pocket in back cover V ACKNOWLEDGEMENTS Many people gave advice, encouragement and assistance, and their help is very deeply appreciated. The author wishes to thank the following persons and organisations in particular: Dr. Charles M. Breen, who supervised the project and gave a great deal of help and encouragement throughout the protracted period of writing-up. His help and "chivvying" are very much appreciated. Prof. C.H. Bornman suggested the project and made the facilities of the Botany Department, University of Natal, available. The author is deeply indebted to Dr. Marinus Werger for his interest and assistance at all stages of the work. Any understanding of the Braun-Blanquet system which has been gained is due to Dr. Werger's clear explanations during many hours of discussion in the course of field work in the Kalahari National Park and in Holland. The laborious task of drawing the phytosociological tables and some of the maps was cheerfully undertaken by Keith Thomson, and the neatness of the final presentation is thanks to his patience and skill. Alan Channing made it possible to obtain aerial photographs and helped with printing of the pictures used. In South West Africa a number of people contributed to the project.- The author is specially grateful to Willi Giess, of the Windhoek Herbarium for his patience in identifying typical "ecologist's specimens." Mr. B.J.G. de la Bat, Director of the Department of Nature Conservation and Tourism assisted with permits to collect specimens and to travel through many areas in the Territory. The Council for Scientific and Industrial Research funded the project as part of the research programme of the Desert Ecological Research Unit and permitted the author to use the data obtained for this thesis. This is gratefully acknowledged. vi The author would like to thank Dr. Mary Seely, Director of the Desert Ecological Research Unit, and all the other people working at Gobabeb for sharing of their experience and help which were so freely given. Drs. Ted Botha and Beth Gibbs-Russell are thanked for the loan of the typewriter used and for typing much of this thesis respectively. Alan and Jenny Channing and my father expended a great deal of effort in overseeing the reproduction and compilation. Their help is deeply appreciated. Finally, the author would like to acknowledge his debt to Dr. K.D. Gordon-Gray, who by her encouragement has done much to stimulate him in an attempt to study plants and vegetation. vii SUMMARY. The geology, topography, soils and climate of the Namib Desert Park south of 23 S. Lat. are described briefly. The vegetation was investigated using the techniques of the Zurich - Montpellier school of phytosociology. Floristic and other site data were collected from 472 sites in the standard Braun - Blanquet manner and the techniques are described in some detail. These data are presented by means of phytosociological tables and detailed descriptions of each community. A total of 34 noda, communities and sub-communities, were delimited in the study area and the floristic and ecological relationships of these are discussed. Only a few of the communities can be assigned to syntaxa from other parts of the world or southern Africa because most of the Namib Desert communities seemed too different to be compared to associations from North Africa, the Middle East, South America or Australia on more than a superficial, structural basis.