Biomes of Southern Africa — an Objective Categorization
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MEMOIRS OF THE BOTANICAL SURVEY OF SOUTH AFRICA MEMOIRS VAN DIE BOTANIESE OPNAME VAN SUID-AFRIKA Republic of South Africa MEMOIRS OF THE BOTANICAL SURVEY OF SOUTH AFRICA No. 54 MEMOIRS VAN DIE BOTANIESE OPNAME VAN SUID-AFRIKA No. 54 BIOMES OF SOUTHERN AFRICA — AN OBJECTIVE CATEGORIZATION by M.C. RUTHERFORD and R.H. WESTFALL Editor/Redakteur: O.A. Leistner ADMINISTRASIE: VOLKSRAAD DEPT. VAN LANQflOU EN WATERVOORSIENING NAVORSINGSINSTITUUT VIR PLANTKUNDE Selling price • Verkoopprys iS (GST excluded/AVB uitgesluit) 1986 - 09-18 Local R4,35 Plaaslik PRETORIA Other countries R5,40 Buitelands '~ BOTANICAL RESEARCH INST*” Post free • Posvry ADMINISTRATION: HOUSF • . DEPT. OF AGRICULTURE AND vka! L« . ISBN 0 621 08862 5 BOTANICAL RESEARCH INSTITUTE — NAVORSINGSINSTITUUT VIR PLANTKUNDE DEPARTMENT OF AGRICULTURE AND WATER SUPPLY — DEPARTEMENT VAN LANDBOU EN WATERVOORSIENING SOUTH AFRICA — SUID-AFRIKA 1986 Foreword The classification of the vegetation of South Africa into conceptually manageable units has received the attention of a large number of botanists in the past. Whereas there is, as can be expected, a reasonable degree of convergence between these broadbased classifications, the differences in many cases were marked. The authors of the present work ascribe these differences mainly to the assumption apparently made by most authors, that subjective assess- ments are acceptable when working on a broad scale. The comparison of the broad scale classifications of vegetation by authors, ranging from Pole Evans (1936) to Huntley (1984) show clearly that a new approach to the delimitation of such units, on a more objective basis, was necessary. Furthermore, the use of the concept of the ‘biome’ by the Inter- national Biological Programme, later adopted by the National Programme for Environmental Sciences of the CSIR, as the basis of the organizational framework, made the classification of vegetation on the basis of biomes a necessity. The fact that the term biome was relatively unknown in South Africa and that no account except an unpublished note by Edwards was available, prompted Huntley to introduce the term and to briefly describe the five biomes he recognized in a short paper he published in 1984. The authors of this memoir, Rutherford and Westfall, can be said to be the first, at least in the South African context, to have studied and defined the concept ‘biome’ in detail and to have delimited the South African biomes on a firm climatological basis. The thoroughness of their approach is exemplary and the result of their studies is a definitive account which should have an impact far wider than the geographical area for which it was written. It is to be anticipated that this reappraisal of the concept of ‘biomes’ and the new approach to their delimitation will induce ecologists to take a new look at this useful biological category. B. DE WINTER Director: Botanical Research Institute Pretoria, February 1985 Contents Page FOREWORD (iii) ABSTRACT AND UITTREKSEL .... 1 1 PERSPECTIVE 3 1.1 Introduction 3 1.2 The Biome concept 3 1.2.1 Review of biome definitions 3 1.2.2 The zoological component 5 1.2.3 The climatic component 6 1.2.4 The plant component — review of life forms 8 1 .3 Definitions of life forms used in this study 11 1.4 Characteristics of life forms 12 1.5 Previously proposed biomes for South or southern Africa 14 1.6 Concluding remarks . 18 2 METHODS 21 2.1 Determination of dominant life forms 21 2.2 Determination of biomes 22 2.3 Determination of climatic patterns 22 2.3.1 Rainfall 22 2.3.2 Temperature 23 2.4 Integration of biome units and climatic pattern 23 2.5 Concluding remarks 24 3 ANALYSIS OF RESULTS 25 3.1 Life forms and biomes 25 3.2 Climate and biomes 25 3.3 Intra-biome interactions 31 3.4 Spatial relationships 33 3.5 Concluding remarks 43 4 DESCRIPTION OF THE BIOMES . 45 4.1 Overview 45 4.2 Desert Biome 45 4.3 Forest Biome 47 4.4 Fynbos Biome 50 4.5 Grassland Biome 53 4.6 Nama-Karoo Biome 55 4.7 Savanna Biome 57 4.8 Succulent Karoo Biome 60 4.9 Comparisons 63 4.10 Concluding remarks 64 5 ECOLOGICAL AND ENVIRONMENTAL RELATIONSHIPS OF DOMINANT LIFE FORMS 67 5.1 Phanerophytes 67 5.2 Chamaephytes 68 5.3 Hemicryptophytes 68 5.4 Therophytes 69 5.5 Concluding remarks 69 6 RATIONALIZATION OF RELATIONS BETWEEN MAPPING SCALE, VEGETATION STRUCTURE AND FLORISTIC COMMUNITY 71 7 CONCLUSIONS 77 ACKNOWLEDGEMENTS 78 REFERENCES 79 APPENDICES 86 (v) Abstract RUTHERFORD, M.C. and WESTFALL, R.H. 1986. The biomes of southern Africa — an objective cate- gorization. Memoirs of the Botanical Survey of South Africa No. 54, pp. 98. Keywords: biome, climate, life form, production, sampling method, scale, southern Africa, veld type, vegetation The biome concept is clarified according to established definitions to permit objective categorization of the major natural systems of southern Africa south of 22° S. Seven biomes were diagnosed according to explicit criteria of dominant and codominant plant life forms at the appropriate scale of 1:10 000 000. These are the Savanna, Nama-Karoo, Grassland, Succulent Karoo, Fynbos, Desert and Forest Biomes. The biomes correlate well with a combination of an index of summer aridity (SAI) and rainfall seasonality. This climatic combination also differentiates the biomes except for the Grassland Biome, the Forest Biome and areas of anthropogenicaily induced invasion of Grassland and Savanna Biomes by elements of the Nama-Karoo Biome. The Grassland Biome is differentiated climatically from Savanna in terms of minimum winter temperature in conjunction with moisture levels. The role of zoological components in biome differentiation appears to be very limited. Absolute annual moisture levels, sometimes associated with edaphic factors, appear to form an appropriate basis for major subdivision of biomes. Ecological implications of the relationship between climate and life form dominance and codominance are discussed. Each biome is systematically described in terms of geographic, biotic, abiotic and resource relations. Various informal approaches to biome categorization in the region illustrate a general lack of appreciation of scale-dependant hierarchical levels. Problems of the relation between mapping scale, vegetation structure and floristic community are elucidated. Uittreksel Die bioom-konsep word in die lig van bestaande definisies verduidelik om ’nobjektiewekategorisering van die belangrikste natuurlike sisteme van suidelike Afrika suid van 22°S daar te steL Sewe biome isvolgens bepaalde maatstawwe van dominante en kodominante plantlewensvorme gediagnoseer op die skaal van 1:10 000 000. Hierdie is die Savanne-, Nama-Karoo-, Grasveld-, Sukkulente Karoo-, Fynbos-, Woestyn-, en Woudbiome. Die biome korreleer goed met ’n kombinasie van ’n indeks van somerariditeit (SAI) en die seisoensverspreiding van die reenval. Hierdie klimaatkombinasie differensieer ook die biome, behalwe die Grasveldbioom, Woudbioom, en gebiede waar die mens indringing van Grasveld- en Savannebiome deur elemente van die Nama-Karoobioom veroorsaak het. Die Grasveldbioom is klimaties van Savanne gedif- ferensieer in terme van minimum wintertemperatuur tesame met vogtigheidsvlakke. Die rol van soologiese komponente in bioomdifferensiasie blyk uiters beperk te wees. Totale jaarlikse vogtigheidsvlakke, soms met edafiese faktore geassosieer, blyk ’n geskikte basis vir die hoofonderverdeling van biome te vorm. Ekologiese implikasies van die verhouding tussen klimaat en lewensvormdominansie en kodominansie word bespreek. Elke bioom word stelselmatig in terme van geografiese, biotiese, abiotiese en hulpbronverhoudings bespreek. Verskeie informele benaderings tot bioomkategorisering in die streek illustreer ’n algemene gebrek aan waardering vir skaal-afhanklike hierargiese vlakke. Probleme in die ver- houding tussen karteringskaal, plantegroeistruktuur en floristiese gemeenskap word toegelig. 1 Digitized by the Internet Archive in 2016 with funding from South African National Biodiversity Institute Libraries https://archive.org/details/biomesofsouthernOOruth 1 Perspective 1 , 1 Introduction This study attempts to categorize the biomes of southern Africa (south of 22° S) objectively. A specific Many attempts have been made to reduce the great effort was made to apply, consistently, each term of spatial and temporal complexity of man’s natural the original definition of a biome (see Section 1.2.1). environment into conceptually manageable units. Often these terms themselves required increased specif- Increasing subject specialization, together with global icity. The advantages of a reasonably rigorous approach expansion, has heightened the problem of dealing with in biome delimitation appears to have been underestimat- this complexity. A larger number of variables tends to ed in most past work. Many researchers appear to have obscure the significant components of large natural assumed that, at this broad scale, subjective assessments systems. Consensus has often been reached on the suffice. This approach suffers from lack of repeatability identification of narrower units of the World’s natural and allows serious bias that often reflects the regional systems, often on the basis of vegetation. At a smaller experiences of the authors concerned. A section on scale, however, with broader areas, consensus on units is methods in biome work is rarely encountered. seldom attained. Many conflicting divisions of natural systems have been proposed and mapped and most 1 .2 The Biome concept authors appear unperturbed by the plethora of different- ly mapped