P.K. Ramachandran Nair An Introduction to Agroforestry KLGWER ACADEMIC PUBLISHERS An Introduction to Agroforestry P.K. Ramachandran Nair Department of Forestry, University of Florida, Gainesville, Florida, U.S.A. Kluwer Academic Publishers DORDRECHT / BOSTON / LONDON IN COOPERATION WITH International Centre for Research in Agroforestry ICRAF Library of Congress Cataloging-in-Publication Data Nair, P. K. R. An introduction to agroforestry / P.K. Ramachandran Na1r. p. cm. Includes bibliographical references and index. ISBN 0-7923-2134-0 (alk. paper) 1. Agroforestry . I. Title. S494.5.A45N3543 1993 634.9'9—dc20 92-46550 ISBN 0-7923-2134-0 Published by Kluwer Academic Publishers, P.O. Box 17, 3300 AA Dordrecht, The Netherlands. Kluwer Academic Publishers incorporates the publishing programmes of D. Reidel, Martinus Nijhoff, Dr W. Junk and MTP Press. Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers, 101 Philip Drive, Norwell, MA 02061, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers Group, P.O. Box 322, 3300 AH Dordrecht, The Netherlands. Printed on acid-free paper All rights reserved © 1993 by Kluwer Academic Publishers No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission from the copyright owners. Printed in The Netherlands Contents Preface xi Acknowledgements xiii Section I. INTRODUCTION 1. The history of agroforestry 3 References 11 2. Definition and concepts of agroforestry 13 Community forestry, farm forestry, and social forestry 16 References 17 Section II. AGROFORESTRY SYSTEMS AND PRACTICES 3. Classification of agroforestry systems 21 3.1. Structural classification of systems 24 3.2. Classification based on function of systems 26 3.3. Ecological classification 28 3.4. Classification based on socioeconomic criteria 30 3.5. A framework for classification 31 3.6. Agroforestry systems and practices 32 References 35 4. Distribution of agroforestry systems in the tropics 39 4.1. The tropical environment 39 4.2. Distribution of tropical agroforestry systems 41 4.3. Agroecological spread of tropical agroforestry systems 48 References 53 v vi Contents 5. Shifting cultivation and improved fallows 55 5.1. System overview 55 5.2. Soil management and shifting cultivation 60 5.3. The evolution of planted fallows 63 5.4. Improved tree fallows 68 References 71 6. Taungya 75 6.1. Soil management 78 6.2. Alternatives and improvements to Taungya 79 References 83 7. Homegardens 85 7.1. Types of homegardens 85 7.2. Structure of homegardens 91 7.3. Food production from homegardens 94 7.4. Research on homegarden systems 95 References 96 8. Plantation crop combinations 99 8.1. Integrated land-use systems with plantation crops 100 8.2. Smallholder systems with coconuts: a notable example of integrated land-use 103 8.3. Crop combinations with other plantation crops 115 8.4. Multistory tree gardens 117 References 121 9. Alley cropping 123 9.1. Nutrient yield 125 9.2. Effect on soil properties and soil conservation 127 9.3. Effect on crop yields 130 9.4. Future directions 134 References 137 10. Other agroforestry systems and practices 141 10.1. Tree fodder and silvopastoral systems 141 10.2. Agroforestry for firewood production 144 10.3. Intercropping under scattered or regularly planted trees 146 10.4. Agroforestry for reclamation of problem soils 150 10.5. Underexploited trees in indigenous agroforestry systems 152 10.6. Buffer-zone agroforestry 153 References 155 Contents vii Section III. AGROFORESTRY SPECIES 11. General principles of plant productivity 161 11.1. Photosynthesis 161 11.2. Plant productivity 165 11.3. Manipulation of photosynthesis in agroforestry 167 References 170 12. Agroforestry species: the multipurpose trees 171 12.1. Multipurpose trees (MPTs) 172 12.2. Herbaceous species 182 References 183 Appendix: short descriptions of multipurpose trees and shrubs (MPTs) commonly used in agroforestry systems 201 13. Component interactions 243 13.1. Positive (production-enhancing) interactions 245 13.2. Negative (production-decreasing) interactions 249 13.3. Component management 254 References 255 Section IV. SOIL PRODUCTIVITY AND PROTECTION 14. Tropical soils 261 14.1. Soil classification: the U.S. soil taxonomy and the FAO legend 261 14.2. Tropical soils 263 References 266 15. Effects of trees on soils 269 15.1. Beneficial effects 271 15.2. Adverse effects 273 References 274 16. Nutrient cycling and soil organic matter 277 16.1. Nutrient cycling in tropical forest ecosystems 277 16.2. Nutrient cycling in agroforestry systems 279 16.3. Improving nutrient cycling efficiency through management 283 16.4. Soil organic matter 289 16.5. Litter quality and decomposition 291 16.6. Trees and biomass production 296 16.7. Role of roots 297 16.8. Conclusions 301 References 303 viii Contents 17. Nitrogen fixation 307 17.1. Rhizobial plants 308 17.2. Actinorhizal plants 311 17.3. Estimation of nitrogen fixation 312 17.4. Technology for exploiting nitrogen-fixing trees in agroforestry 315 17.5. Future trends in N2 fixation research in agroforestry 319 References 319 18. Soil conservation 325 18.1. Changing concepts and trends 327 18.2. Measurement of soil erosion 328 18.3. Effect of agroforestry on erosion factors 328 18.4. Erosion rates under agroforestry 331 18.5. Trees as windbreaks and shelterbelts 333 18.6. Erosion control through agroforestry in practice 338 References 343 Section V. DESIGN AND EVALUATION OF AGROFORESTRY SYSTEMS 19. The diagnosis and design (D & D) methodology 347 19.1. The genesis of D & D 347 19.2. Concepts and procedures of D & D 348 19.3. Key features of D & D 351 19.4. Variable scale D & D procedures 352 19.5. Comparison of D & D with similar methodologies 355 References 356 20. Field experiments in agroforestry 357 20.1. Agroforestry research: different perspectives 358 20.2. Principles of field experimentation 361 20.3. Special considerations in agroforestry experiments 362 20.4. The current state of agroforestry field experimentation 368 20.5. Prognosis of the directions in agroforestry research 370 References 372 21. On-farm research 375 21.1. General considerations 375 21.2. Modified stability analysis of on-farm trial data 377 21.3. On-farm research in agroforestry 379 21.4. Methodologies for on-farm research in agroforestry 380 21.5. Conclusions 382 References 382 Contents ix 22. Economic considerations 385 22.1. General principles of economic analysis 385 22.2. Financial and economic analyses 389 22.3. Project analysis 391 22.4. Past and recent economic studies of agroforestry 406 22.5. Conclusions 408 References 408 23. Sociocultural considerations 413 23.1. Agroforestry as a social science 413 23.2. Important sociocultural factors in agroforestry 414 23.3. Farmer's perception of tree planting 418 23.4. Government policies and agroforestry implementation 421 23.5. Social acceptability of agroforestry 423 References 425 24. Evaluation of agroforestry systems 429 24.1. Productivity evaluation 429 24.2. Sustainability evaluation 432 24.3. Adoptability evaluation 434 24.4. Towards development of a methodology for evaluating agroforestry systems 435 References 438 Section VI. AGROFORESTRY IN THE TEMPERATE ZONE 25. Agroforestry in the temperate zone 443 25.1. Characteristics of temperate-zone agroforestry 443 25.2. Historical perspective 445 25.3. Current temperate-zone agroforestry systems 446 25.4. Opportunities and constraints 462 References 465 Glossary 469 List of acronyms and abbreviations 483 SI units and conversion factors 485 Subject index 491 Preface Agroforestry has come of age during the past fifteen years. During this period, activities and interest in agroforestry education and training have increased tremendously, as in other aspects of agroforestry development. Today, agroforestry is taught at the senior undergraduate and postgraduate levels in many institutions around the world, either as a separate subject or as a part of the regular curricula of agriculture, forestry, ecology, and other related programs. Although several books on the subject have been published during the past few years, there is still no single publication that is recognized as a textbook. This book is an effort to make up for this deficiency. The need for such a book became obvious to me when I was faced with the task of teaching a graduate-level course in agroforestry at the University of Florida five years ago. Subsequently, the Second International Workshop on Professional Education and Training held here at the University of Florida in December 1988 recommended that the preparation of an introductory textbook be undertaken as a priority activity for supporting agroforestry education world-wide. The various educational and training courses that I have been involved in, and my interactions with several instructors and students of agroforestry in different parts of the world, further motivated me into this venture. Agroforestry is a very complex subject; indeed, it is an amalgam of many subjects. For centuries, agroforestry has been artfully practiced throughout the world, especially in the developing countries of the tropics. Lately, the underlying principles of these time-tested practices, as well as the scope for applying scientific principles to improve them, are being explored vigorously. It has now become obvious that the science of agroforestry does, or ought