SCLEROCARYA BIRREA A MONOGRAPH SCLEROCARYA BIRREA A MONOGRAPH Edited by John B. Hall, E. M. O'Brien and Fergus L. Sinclair School of Agricultural and Forest Sciences, University of Wales, Bangor, U.K. 2002 Veld Products Research & Development Cite as: Hall, J.B., O'Brien, E.M., Sinclair, F.L. 2002. Sclerocarya birrea: a monograph. School of Agricultural and Forest Sciences Publication Number 19, University of Wales, Bangor. 157 pp. ISSN: 0962-7766 ISBN: 1 84220 049 6 School of Agricultural and Forest Sciences Publication Number: 19 © 2002 University of Wales, Bangor. All rights reserved. Front cover: Extracting marula juice manually in Namibia, using a cow horn to separate the skin from the flesh. Oil is later extracted from the kernels. (PRshots.com and The Body Shop) Back cover: Sclerocarya birrea subsp. caffra: extracted whole kernels – South Africa (C Geldenhuys) DEDICATION This monograph is dedicated to the memory of Dr Abdou-Salam Ouédraogo, whose knowledge of the ecology and biology of the economic trees of West Africa’s parklands was unrivalled. Dr Ouédraogo, of the Centre National de Semences Forestières, Burkina Faso, and the International Plant Genetic Resources Institute, was tragically a victim of the air disaster off the West African coast on the 30th January 2000. i ACKNOWLEDGEMENTS We take this opportunity to thank in particular several research and rural development specialists who have generously given access to documents reporting important new surveys and evaluations of Sclerocarya birrea: Sheona and Charlie Shackleton of Rhodes University, South Africa; Roger Leakey of James Cook University, Australia; Caroline Agufa of ICRAF, Kenya and Susan Barton, Mineworkers Development Agency, South Africa. We are grateful to Coert Geldenhuys, PRshots.com and The Body Shop for making their photographic images available for use in this publication. Karen Cooper, Michelle Jones and Emma Youde, School of Agricultural and Forest Sciences, University of Wales, Bangor, have provided extensive office support and organized the final document. Jeremy Williams, using the School’s Geographic Information Systems facility, prepared the maps. Pat Denne, Mike Hale and Jon Tuson assisted with comments and illustrations for the account of the wood of the species. Charlie Shackleton and Susan Barton provided welcome comment on several other chapters. Permission for Eileen O’Brien to examine holdings of Sclerocarya at the Royal Botanic Gardens (Kew), the Natural History Museum (London), the Daubeny Herbarium (Oxford), Muséum National d’Histoire Naturelle (Paris) and the National Botanic Garden of Belgium (Meise) is gratefully acknowledged. This publication is an output from a research project funded by the United Kingdom Department for International Development (DFID) for the benefit of developing countries. The views expressed are not necessarily those of DFID. R7227, Forestry Research Programme. iii FOREWORD Sclerocarya birrea ranks among a select group of wide-ranging African trees that have remained essentially wild, despite having had major cultural and economic roles dating back for centuries. Sclerocarya is still important for sustaining rural livelihoods today and there is much recent interest in its domestication and commercialisation, both to protect the tree as a resource and to sustainably exploit it to increase the income and food security of rural people within its natural range. A little over 20 years ago, A K Shone drew together a wealth of information about this fascinating tree in a Bulletin published by the South African Department of Forestry, which remains an indispensable study for anyone concerned with the species in the South African part of the range. There have been many developments involving Sclerocarya since Shone wrote his bulletin, notably a burgeoning interest in its commercial potential and increasing awareness of its significance elsewhere in Africa, on both sides of the equator. This new monograph on the species re-assesses our knowledge of the species and brings it up to date, expanding the context in which the tree is considered to cover the whole of its vast natural range, and covering its emerging commercial potential that is making the tree significant far beyond the local communities which have used and conserved it into present times. Fergus L. Sinclair School of Agricultural and Forest Sciences University of Wales, Bangor v LIST OF CONTRIBUTORS Name Institution Professor O.T. Edje Crop Production Department, Faculty of Agriculture, University of Swaziland, Luyengo, Swaziland Dr John B. Hall School of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd, LL57 2UW, UK Tel: +44 1248 382446; Fax: +44 1248 38 2459 Email: [email protected] Dr Hannah Jaenicke World Agroforestry Centre, PO Box 30677, Nairobi, Kenya Mr Moses Munjuga World Agroforestry Centre, PO Box 30677, Nairobi, Kenya Dr Bernard Muok Kenya Forestry Research Institute, P O Box 892, Kitui, Kenya Dr Eileen M. O’Brien School of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd, LL57 2UW, UK Mr Kago Phofuetsile Veld Products Research & Development, Box 2020, Gaborone, Botswana Dr Fergus L. Sinclair School of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd, LL57 2UW, UK Ms Margaret K. Thiong’o World Agroforestry Centre, P O Box 30677, Nairobi, Kenya Ms Emma Youde School of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd, LL57 2UW, UK vii TABLE OF CONTENTS DEDICATION..........................................................................................................................I ACKNOWLEDGEMENTS..................................................................................................III FOREWORD...........................................................................................................................V LIST OF CONTRIBUTORS.............................................................................................. VII 1 IMPORTANCE ...................................................................................................................1 2 ECOLOGY........................................................................................................................... 7 2.1 DISTRIBUTIONAL CONTEXT ................................................................................... 7 2.1.1 Affinities................................................................................................................... 7 2.1.2 Fossil record............................................................................................................8 2.1.3 Origin ...................................................................................................................... 8 2.1.4 Present distribution ............................................................................................... 10 2.2 ENVIRONMENTAL FACTORS IN DISTRIBUTION .............................................. 11 2.2.1 Elevation................................................................................................................11 2.2.2 Climate ..................................................................................................................11 2.2.3 Geology and soils .................................................................................................. 14 2.2.4 Toposequences....................................................................................................... 15 2.3 SITE.............................................................................................................................. 16 2.4 SCLEROCARYA BIRREA AS A VEGETATION COMPONENT............................... 16 2.4.1 Chorology and vegetation types ............................................................................ 16 2.4.2 Community composition ........................................................................................ 17 2.4.3 Prominence, population levels and representation ............................................... 30 2.4.4 Interactions involving Sclerocarya birrea within communities............................. 35 3 BIOLOGY.......................................................................................................................... 45 3.1 CHROMOSOME COMPLEMENT............................................................................. 45 3.2 LIFE CYCLE AND PHENOLOGY............................................................................. 45 3.2.1 Life cycle................................................................................................................ 45 3.2.2 Phenology.............................................................................................................. 48 3.2.3 Year-to-year variation in flowering and fruiting................................................... 49 3.3 REPRODUCTIVE BIOLOGY..................................................................................... 49 3.3.1 Pollen..................................................................................................................... 49 3.3.2 Sexuality ................................................................................................................50 3.3.3 Anthesis .................................................................................................................50 3.3.4 Pollination and potential pollinators .................................................................... 50 3.3.5 Fruit development and seed set ............................................................................