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Land resources of the Solomon Islands Volume 6 Choiseul and the Shortland Islands i6"M^ A deep, well drained, reddish clay Tropohumult overlying finely banded Moli Sediments on Moli Island 1 I Land Resources Division Land resources of the Solomon Islands Volume 6 Choiseul and the Shortland Islands J R D Wall and J R F Hansell Land Resource Study 18 Land Resources Division, Ministry of Overseas Development Tolworth Tower, Surbiton, Surrey, England KT6 7DY 1976 THE LAND RESOURCES DIVISION me L.OIIU iicauuii/co uivtaiuii ui Li ic mil nau y ui uvci scaa L^cvciu|j||iei IL aaai3L3 ucvciupil ILJ countries in mapping, investigating and assessing land resources, and makes recommenda­ tions on the use of these resources for the development of agriculture, livestock husbandry and forestry; it also gives advice on related subjects to overseas governments and organisations, makes scientific personnel available for appointment abroad and provides lectures and training courses in the basic techniques of resource appraisal. The Division works in close co-operation with government departments, research institutes, universities and international organisations concerned with land resources assessment and development planning. IV List of volumes Title: Land resources of the Solomon Islands. J R F Hansell and J R D Wall Volume 1 Introduction and recommendations Volume 2 Guadalcanal and The Florida Islands Volume 3 Malaita and Ulawa Volume 4 New Georgia Group and the Russell Islands Volume 5 Santa Isabel Volume 6 Choiseul and the Shortland Islands Volume 7 San Cristobal and adjacent islands Volume 8 Outer Islands During the course of the production of these reports, the name of the British Solomon Islands Protectorate was changed to the Solomon Islands. The former name has been used throughout the first two volumes to be published (2 and 3), in the text (but not on the covers) of Volumes 4 and 7, and not at all in the remaining volumes (1, 5, 6 and 8). v I s Contents LIST OF FIGURES x LIST OF PLATES x LIST OF STEREOPAIRS x LIST OF MAPS xi PART1 INTRODUCTION 1 Preface 1 Abstract 1 Résumé 2 Descriptors for co-ordinate indexing 2 PART2 THE ENVIRONMENT 3 Introduction 3 Factors in the determination of potential land use 3 Environmental factors 3 Location 5 Physiographic Regions 5 I Eastern islands 5 II Eastern ridges 6 I III Eastern lowlands 6 IV East-central highlands 6 V Maetambe volcanic centre 8 i VI Southern karstlands and ridges 8 VII Central plateaux 8 VIM Central ridges and hills 9 IX Northern karst and hills 9 1 X Fauro, Alu and nearby islands 10 1 XI Mono 10 I VII Landforms 10 High ridges 10 Rounded ridges 15 Young volcanic centres 16 Hilly plateaux 16 Low hills and ridges 25 Cuestas 25 Karstic areas 26 Karst 26 Terraces 29 Fluvial plains 29 Swamps 30 Littoral landforms 31 Soils 31 Introduction 31 Organic soils with mostly we 11-decomposed peat (Histosols: 33 Folists, Hemists) Young soils with little or no horizon development 35 (Entisois: Aquents, Psamments, Fluvents, Orthents) Slightly weathered soils with little horizon development 39 (Inceptisols: Tropepts) Weakly weathered soils with a thick dark topsoil and high base 42 status (Mollisols: Rendolls, Udolls) Moderately to strongly weathered and leached soils with high 43 base status (Alfisols: Udalfs) Strongly weathered and leached soils with low base status 44 (Ultisols: Humults) Very strongly weathered and leached soils (Oxisols: Orthox) 44 Current Land Use 46 Introduction 46 Shifting cultivation 47 Cash crops 47 Cattle 49 Land use pattern 49 Forests 52 PART 3. LANDSCAPE ANALYSIS: LAND REGIONS AND LAND SYSTEMS 53 Introduction 53 Kaipito Land Region 56 1. Kumbongava, 2. Posarae, 3. Taora Ghausava Land Region 62 4. Marapa, 5. Mbina Paru Land Region 66 6. Aroaro, 7. Aruliho, 8. Esperance, 9. Falamae, 10. Hisiai, 11. Ibatasi, 12. Kavakava, 13. Malanjili, 14. Panggoe Manawai Land Region 84 15. Andi, 16. Henefau, 17. Huranja, 18. Mbaeroko Kwainangali Land Region 92 19. Fata'olo, 20. Mono, 21.Sui Mbetilonga Land Region 98 22. Balo, 23. Rirama, 24. Sakatokana, 25. Sepa, 26. Tirua VIM Rokera Land Region 108 27. Aiokan, 28. Kohinggo Fiu Land Region 112 29. Kumotu, 30. Lomousa, 31. Manggo, 32. Pusuraghi, 33. Tenaru PART 4. THE AGRICULTURAL POTENTIAL OF THE LAND REGIONS 123 Introduction 123 Kaipito Land Region 124 Ghausava Land Region 125 Paru Land Region 125 Areas of low agricultural potential 126 Areas of low to moderate agricultural potential 126 Areas of moderately high agricultural potential 126 Manawai Land Region 127 Kwainangali Land Region 128 Mbetilonga Land Region 129 Tirua, Sakatokana and Rirama Land Systems 129 Balo Land System 130 Rokera Land Region 130 Fiu Land Region 132 Kumotu and Pusuraghi Land Systems 132 Lomousa and Tenaru Land Systems 132 Manggo Land System 133 PART 5. AGRICULTURAL OPPORTUNITY AREAS 135 Introduction 135 Poroporo 136 Pemba 137 Pachö 138 Ghaghara 140 Vaghena 141 Balo 143 Mono 143 PART 6. REFERENCES AND RELEVANT WORKS 145 APPENDIXES 149 1 Selected soil profile descriptions 149 2 Definition of geomorphological parameters 187 3 Soil analysis methods and definitions of pedological parameters 193 4 Sample area studies 195 IX LIST OF FIGURES 6-1 Cross-section of central Choiseui showing inferred relationships 11 between land systems, geology and landforms 6-2 Diagrammatic cross-section across Mono Island showing lithology, 27 soil, landform and vegetation relationships 6-3 Diagrammatic cross-section across north-east Choiseui showing lithology, 27 soil, landform and vegetation relationships 6-4 Diagrammatic cross-section near Ghaghara, east Choiseui, showing 28 lithology, soil, landform and vegetation relationships 6-5 Diagrammatic cross-section of area near Mboemboe showing lithology, 28 soil, landform and vegetation relationships 6-6 Changes of soil properties with depth in selected Choiseui profiles 36 LIST OF STEREOPAIRS 6-1 An area of mixed geology in which limestones are predominant in 17 the south, forming partly drowned cockpit karst; 6-2 Raised and tilted beds of limestone and fine-grained calcareous 18 sediments on Mono Island forming terraces 6-3 An uncultivated area of north Choiseui underlain by limestone or 19 calcareous, fine-grained sediments 6-4 A ridged landscape of north-central Choiseui with mainly early 20 Tertiary basalts and recent volcanic sediments 6-5 The volcanic footslopes of Mount Maetambe in the north-east, 21 separated from ridges of metamorphosed basement rocks by an inferred zone of limestone which reoccurs as karst terrain in the south 6-6 Tuffaceous sediments, pyroclastics and lavas underlie ridges and 22 flat-topped hills east of Mount Maetambe. Narrow volcanic sand beaches and swamps occur in coastal areas 6-7 Low-lying Vaghena Island contains tidal mangrove and freshwater 23 swamps. Lagoonal sediments form level platforms or low rolling ridges. 6-8 The extinct volcano of Kumboro Peak with andesitic pyroclastics 24 comprises rugged ridges radiating from a central point. Volcanic material over limestone forms the northern slope. PLATES Frontispiece A deep, well drained reddish clay Tropohumult overlying finely banded Moli Sediments on Moli Island 6-1 Drowned cockpit karst at Poro, west-central Choiseui 7 6-2 The Mbina Land System of eastern Choiseui with 7 specialised lowland forest vegetation x TEXT MAPS 15 Study area location 16 Landforms SAMPLE AREA MAPS IN APPENDIX 4 CA Alu CB Mono CC Chirovanga SEPARATE MAPS (in separate folder) 6a Physiography and physiographic regions 6b Catchment areas 6c Soil sample sites and traverses 6d Soil associations 6e Land systems and land regions 6f Land use, 1962-8 6g Agricultural opportunity areas 6h Forest types XI Parts 1-6 CORRECTION LAND RESOURCE STUDY 18 VOLUME 6 Page 26, paragraph 1, line 2, for eroding read erode Page 26, paragraph 6, line 2, for convex read concave Page 39, paragraph 3, line 2, for or read that Page 138 last line, for the read and Parti Introduction PREFACE This volume deals with the major island of Choiseul, an archipelago of small islands in the east dominated by Vaghena and, to the west, the Shortland group with the main islands of Mono (Treasury), Alu (Shortland) and Fauro. This report is one of a series of volumes describing the land resources of the Solomon Islands. Each is concerned with a major island or island group and incorporates the results of fieldwork, the subsequent land classification and the assessment of its agricultural potential. Reports are issued on an island-by-island basis to simplify district planning and to facilitate access to the recommendations. Landforms and soils are described fully in this volume as together they form the basis of the land classification, but other aspects of the physical environment such as geology, climate and vegetation are given only cursory attention, having been more fully described in Volume 1. Similarly, aspects of the cultural environment which are unique to the islands are discussed in this volume while a fuller discussion of popula­ tion and subsistence agriculture, for example, can be found in Volume 1. With this method of presentation, unnecessary repetition is avoided and it is possible to separate fieldwork data from information largely derived from published material. The system of measurement used in this report is metric, with the exception of the sample area studies of Appendix 4 for which original measurements were in the imperial system.