COMMITTEE ON SUSTAINABLE AGRICULTURE AND THE ENVIRONMENT IN THE HUMID TROPICS pot

Sustainable Agriculture
and the Environment in
the
Committee on Sustainable Agriculture and the Environment in the
Humid Tropics
Board on Agriculture
and
Board on Science and Technology for International Development
National Research Council
NATIONAL ACADEMY PRESS
Washington, D.C. 1993
i
HUMID TROPICS
ii
NATIONAL ACADEMY PRESS 2101 Constitution Avenue Washington, DC 20418
NOTICE: The project that is the subject of this report was approved by the Governing Board of the
National Research Council, whose members are drawn from the councils of the National Academy
of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of
the committee responsible for the report were chosen for their special competences and with regard
for appropriate balance.
This report has been reviewed by a group other than the authors according to procedures
approved by a Report Review Committee consisting of members of the National Academy of Sci-
ences, the National Academy of Engineering, and the Institute of Medicine.
This report has been prepared with funds provided by the Office of Agriculture, Bureau for
Research and Development, U.S. Agency for International Development, under Amendment No. 2
of Cooperative Agreement No. DPE-5545-A-00-8068-02. Partial funding was also provided by the
Office of Policy Analysis of the U.S. Environmental Protection Agency through this cooperative
agreement. The U.S. Agency for International Development reserves a royalty-free and nonexclu-
sive and irrevocable right to reproduce, publish, or otherwise use and to authorize to use the work
for government purposes.
Cover illustration by Michael David Brown © 1987.

Library of Congress Cataloging-in-Publication Data
National Research Council (U.S.). Committee on Sustainable Agriculture and the Environment in
the Humid Tropics.
Sustainable agriculture and the environment in the humid tropics / Committee on Sus-
tainable Agriculture and the Environment in the Humid Tropics, Board on Agriculture
and Board on Science and Technology for International Development, National Research
Council.
p. cm.
Includes bibliographical references and index.
ISBN 0-309-04749-8
1. Agricultural systems—Tropics. 2. Sustainable agriculture—Tropics. 3. Land use, Rural
—Tropics. 4. Agricultural ecology—Tropics. I. Title.
S481.N38 1992
92-36869
333.76′15′0913—dc20
CIP
© 1993 by the National Academy of Sciences. All rights reserved.
No part of this book may be reproduced by any mechanical, photographic, or electronic process, or
in the form of a phonographic recording, nor may it be stored in a retrieval system, transmitted, or
otherwise copied for public or private use without written permission from the publisher, except for
the purposes of official use by the U.S. government.
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of
the author(s) and do not necessarily reflect the view of the organizations or agencies that provided
support for this project.
Printed in the United States of America
COMMITTEE ON SUSTAINABLE AGRICULTURE AND
THE ENVIRONMENT IN THE HUMID TROPICS
RICHARD R. HARWOOD, Chair, Michigan State University
MARY E. CARTER, U.S. Department of Agriculture
RODRIGO GÁMEZ, Instituto Nacional de Biodiversidad, Costa Rica

STEPHEN R. GLIESSMAN, University of California, Santa Cruz
ARTURO GÓMEZ-POMPA, University of California, Riverside
LOWELL S. HARDIN, Purdue University
WALTER A. HILL, Tuskegee University
RATTAN LAL, Ohio State University
GILBERT LEVINE, Cornell University
ARIEL E. LUGO, U.S. Department of Agriculture, Forest Service, Puerto Rico
ALISON G. POWER, Cornell University
VERNON W. RUTTAN, University of Minnesota
PEDRO A. SANCHEZ, International Center for Research in Agroforestry, Kenya
E. ADILSON SERRÃO, Center for Agroforestry Research of the Eastern
Amazon, Brazil
PATRICIA C. WRIGHT, State University of New York, Stony Brook
Staff
MICHAEL MCD. DOW, Study Director
CARLA CARLSON, Senior Staff Officer
CURT MEINE, Staff Associate
BARBARA J. RICE, Staff Associate and Editor
JANET L. OVERTON, Associate Editor
DAVID HAMBRIC, Senior Project Assistant
ALWIN PHILIPPA, Senior Program Assistant
iii
BOARD ON AGRICULTURE
THEODORE L. HULLAR, Chair, University of California, Davis
PHILIP H. ABELSON, American Association for the Advancement of Science
DALE E. BAUMAN, Cornell University
R. JAMES COOK, Agricultural Research Service at Washington State University
ELLIS B. COWLING, North Carolina State University
PAUL W. JOHNSON, Natural Resources Consultant, Decorah, Iowa
NEAL A. JORGENSEN, University of Wisconsin

ALLEN V. KNEESE, Resources for the Future, Inc.
JOHN W. MELLOR, John Mellor Associates, Inc.
DONALD R. NIELSEN, University of California, Davis
ROBERT L. THOMPSON, Purdue University
ANNE M. K. VIDAVER, University of Nebraska
JOHN R. WELSER, The Upjohn Company
Staff
SUSAN OFFUTT, Executive Director
JAMES E. TAVARES, Associate Executive Director
CARLA CARLSON, Director of Communications
BARBARA J. RICE, Editor
iv
BOARD ON SCIENCE AND TECHNOLOGY FOR
INTERNATIONAL DEVELOPMENT
ALEXANDER SHAKOW, Chair, The World Bank
PATRICIA BARNES-MCCONNELL, Michigan State University
JORDAN J. BARUCH, Jordan Baruch Associates
BARRY BLOOM, Albert Einstein College of Medicine
JANE BORTNICK, Library of Congress
GEORGE T. CURLIN, National Institutes of Health
DIRK FRANKENBERG, University of North Carolina, Chapel Hill
RALPH W. F. HARDY, Boyce-Thompson Institute for Plant Research, Inc.
FREDRICK HORNE, Oregon State University
ELLEN MESSER, Brown University
CHARLES C. MUSCOPLAT, MCI Pharma, Inc.
JAMES QUINN, Dartmouth College
VERNON W. RUTTAN, University of Minnesota
ANTHONY SAN PIETRO, Indiana University
ERNEST SMERDON, University of Arizona
Ex Officio Members

GERALD P. DINEEN, Foreign Secretary, National Academy of Engineering
JAMES B. WYNGAARDEN, Foreign Secretary, National Academy of Sciences
Staff
MICHAEL MCD. DOW, Acting Director
E. WILLIAM COLGLAZIER, Executive Director, Office of International Affairs
v
The National Academy of Sciences is a private, nonprofit, self-perpetuating
society of distinguished scholars engaged in scientific and engineering
research, dedicated to the furtherance of science and technology and to their
use for the general welfare. Upon the authority of the charter granted to it by
the Congress in 1863, the Academy has a mandate that requires it to advise
the federal government on scientific and technical matters. Dr. Frank Press is
president of the National Academy of Sciences.
The National Academy of Engineering was established in 1964, under the
charter of the National Academy of Sciences, as a parallel organization of
outstanding engineers. It is autonomous in its administration and in the
selection of its members, sharing with the National Academy of Sciences the
responsibility for advising the federal government. The National Academy of
Engineering also sponsors engineering programs aimed at meeting national
needs, encourages education and research, and recognizes the superior
achievements of engineers. Dr. Robert M. White is president of the National
Academy of Engineering.
The Institute of Medicine was established in 1970 by the National Academy
of Sciences to secure the services of eminent members of appropriate
professions in the examination of policy matters pertaining to the health of
the public. The Institute acts under the responsibility given to the National
Academy of Sciences by its congressional charter to be an adviser to the
federal government and, upon its own initiative, to identify issues of medical
care, research, and education. Dr. Kenneth I. Shine is president of the
Institute of Medicine.

The National Research Council was organized by the National Academy of
Sciences in 1916 to associate the broad community of science and
technology with the Academy’s purposes of furthering knowledge and
advising the federal government. Functioning in accordance with general
policies determined by the Academy, the Council has become the principal
operating agency of both the National Academy of Sciences and the National
Academy of Engineering in providing services to the government, the public,
and the scientific and engineering communities. The Council is administered
j
ointly by both Academies and the Institute of Medicine. Dr. Frank Press and
Dr. Robert M. White are chair and vice chair ,
respectively, of the
National
Research Council.
www.national-academies.org
vi
man
man
-
Preface
The increasingly adverse effects of human activities on the earth's land,
water, atmospheric, and biotic resources have clearly demonstrated that a new
attitude of stewardship and sustainable management is required if our global
resources are to be conserved and remain productive. Nowhere is this need more
urgent than in the world's humid tropics. Its populations, many subsisting at or
below the poverty level, will continue to rely on the resource base to meet their
needs. That base must be stabilized while becoming increasingly productive.
Thoughtful and prompt actions, especially positive policy changes, are required to
break the current pattern of unplanned deforestation in the humid tropics, to
reverse environmental degradation caused by improper or mismanaged crop and

animal production systems, and to revitalize abandoned lands.
At the request of the U.S. Agency for International Development (USAID),
the National Research Council's Board on Agriculture and the Board on Science
and Technology for International Development convened the 15-member
Committee on Sustainable Agriculture and the Environment in the Humid
Tropics. The U.S. Environmental Protection Agency also provided support,
emphasizing its interest in the global environmental implications of the problem.
The study responds to the recognized need for sustainable land use systems
that (1) maintain the long-term biological and ecological integrity of natural
resources, (2) provide economic returns at the farm level, (3) contribute to quality
of life of rural populations, and
PREFACE vii
(4) integrate into national economic development strategies. In particular, the
committee was asked to identify and analyze key problems of agricultural
practices that contribute to environmental degradation and result in declining
agricultural production in humid tropic environments.
The committee began its work in March 1990. It sought to understand the
overarching environmental, social, and policy contexts of land conversion and
deforestation—and the promise of sustainable land uses—by integrating the
views of experts in the broad areas of agriculture, ecology, and social sciences.
Its work focused on the range of land use systems appropriate to the forest
boundary, an area where agriculture and forestry merge in a continuum of
production types involving trees, agricultural crops, and animals. The committee
addressed intensive, high-input agriculture only as it relates to common
environmental problems. The committee undertook supplemental analyses of
tropical forest land use policies and the effects of tropical land use on global
climate change. We sought a wide range of scientific data, specialized
information, and expert views to address our broad charge.
A critical component of the humid tropics equation that was not within the
scope of the study is human population. The committee acknowledges population

dynamics as a major factor in achieving sustainable land use and development in
the humid tropics; the land use systems it describes fit a broad range of
population densities. We stress the importance of population issues, particularly
in this region of the world, but an analysis of population densities, pressures, and
trends was not part of our study, nor does the composition of the committee
reflect the demographic expertise necessary to address population issues.
This report, Sustainable Agriculture and the Environment in the Humid
Tropics, will contribute to the elusive “solution” to tropical deforestation through
its outline of a variety of approaches to tropical land use and conservation. Each
land use option would take advantage of the opportunities inherent in physical
resource patterns, labor, market availability, and social setting, and each would
contribute to the common goal of sustainability in the humid tropics.
The land use options scheme in Chapter 2 and its accompanying table for
evaluating land use attributes can be used as a guide in decision making. The
presentation makes the information usable by in-country decision makers, from
the local level on up, as well as by governmental and nongovernmental agencies.
We believe the information in this report will be helpful to researchers, planners,
and policymakers in industrialized countries and in developing countries.
PREFACE viii
Part One is the committee's deliberative report. It emphasizes the restoration
of degraded land, the importance of general economic growth as an alternative to
forest exploitation, and the need for comprehensive management of forest and
agricultural resources. The underlying premise of the committee's work is that
under conditions of economic and social pressure, what is not managed today is
at risk of being lost tomorrow.
Within Part One, the Executive Summary discusses the findings of the
committee and presents key recommendations. Chapter 1 describes the humid
tropics, the consequences of forest conversion and deforestation, environmental
factors affecting agriculture, and the fostering of sustainable land use in the
humid tropics. Chapter 2 discusses major land use options that local, regional, and

national managers might choose in making decisions to achieve food production
goals, maintain or increase local income levels, and protect the natural resource
base. Chapter 3 discusses technical research needs and presents recommendations
on land use options. Chapter 4 presents policy imperatives to promote
sustainability. The Appendix to Part One presents a discussion of emissions of
greenhouse gases associated with land use change.
To enhance its understanding, the committee commissioned a series of
country profiles to gather information on land use and forest conversion in
different countries, to evaluate general causes and consequences within specific
contexts, to identify sustainable land use alternatives, and to compare policy
implications. Seven country profiles are presented in Part Two. Authors review
agricultural practices and environmental issues in Brazil, Côte d'Ivoire,
Indonesia, Malaysia, Mexico, the Philippines, and Zaire.
The committee's intent in this report is to make a positive statement about
the potential benefits of sustainable agriculture in the humid tropics, rather than to
condemn the forces that have contributed to the current situation. It is an attempt
to promote the restoration and rehabilitation of already deforested lands, to
increase their productivity, and to explore the policy changes required to take the
next steps toward sustainability. Guidelines for future research and policy,
whether for conserving natural ecosystems or for encouraging sustainable
agroecosystems, must be designed with a global perspective and within the
context of each country's environment, history, and culture.
The committee underscores the fact that sustainable agriculture in any given
country will consist of many diverse production systems, each fitting specific
environmental, social, and market niches. Some alternatives require higher
inputs, labor, or capital—depending
PREFACE ix
on their makeup, resource base, and environment—but each must become more
sustainable. Conversely, each system can contribute toward the sustainability of
the agricultural system in general by helping to meet the varied and changing

needs facing countries in the humid tropics. To maintain a diversity of
approaches while making real progress toward common goals is the challenge
that confronts all who are concerned with the future of the lands and people of the
humid tropics.
RICHARD R. HARWOOD, Chair
Committee on Sustainable
Agriculture and the Environment in the Humid Tropics
PREFACE x
Acknowledgments
The disciplines, multidisciplinary experiences, expertise, and countries of
the world that are represented by the many individuals who have generously
contributed to this report constitute a very long list. Because of the efforts of the
many who shared ideas and offered background knowledge, the committee was
able to expand its views of issues relating to sustainable agriculture and the
environment in the humid tropics and benefit from a variety of perspectives.
Among the many individuals whose work was of special significance to this
report are the authors of the appended paper, the country profiles, and their
collaborators. The descriptive data and analyses presented in the seven country
profiles, contained in Part Two of the report, provided much of the foundation for
the committee's work. In addition to the authors and their collaborators, the
committee acknowledges the contributions of Cyril B. Brown, Purdue
University; Avtar Kaul, Winrock International; Daniel Nepstad, Woods Hole
Research Center; and Christopher Uhl, Pennsylvania State University. (Both
Nepstad and Uhl are associated with the Center for Agroforestry Research of the
Eastern Amazon, Belém, Brazil.) Michael Hayes provided valuable editorial
assistance in preparing the country profiles for publication.
To broaden its information resources, the committee convened two regional
meetings on agricultural and environmental practices and policies in the humid
tropics. The first meeting was held at the
ACKNOWLEDGMENTS xi

Faculty of Agronomy, University of Costa Rica, in San Jose. The second was
held in Bangkok, Thailand, under the auspices of the Asian Regional Office of
the National Research Council.
During the course of its deliberations, the committee sought the counsel and
advice of independent scholars and individuals representing a range of
organizations. Among those who gave generously of their experience were
Robert O. Blake, Committee on Agricultural Sustainability for Developing
Countries; Erick Fernandes, Thurman Grove, and Cheryl Palm, North Carolina
State University; Douglas Lathwell, Cornell University; Charles H. Murray, Food
and Agriculture Organization of the United Nations; Stephen L. Rawlins, U.S.
Department of Agriculture; R. D. H. Rowe, World Bank; Roger A. Sedjo,
Resources for the Future; and John S. Spears, Consultative Group on
International Agricultural Research. The assistance of Andrea Kaus and
Veronique M. Rorive, University of California at Riverside, was also helpful to
the committee.
Research assistance was provided by three student interns, who were
sponsored by the Midwest Universities Consortium for International Activities,
Inc. The committee extends special thanks to Joi Brooks, University of Illinois at
Urbana, and Jil Reifschneider and Kristine Agard, University of Wisconsin.
The committee is grateful to Curt Meine and Barbara Rice, whose skill and
teamwork transformed imperfect and incomplete draft materials into a
comprehensive report. We are particularly grateful to Jay Davenport, whose
insights and support were invaluable to the committee throughout the course of
the study.
And the committee especially recognizes the efforts of Pedro Sanchez, who
served as committee chairman until assuming responsibilities as director general
of the International Center for Research in Agroforestry, Nairobi, Kenya.
ACKNOWLEDGMENTS xii
Contents
EXECUTIVE SUMMARY 1

Findings 2
Landscape Management: A Global Requirement 4
The Humid Tropics 5
Sustainable Land Use Options 8
Recommendations 12
Conclusion 17
PART ONE
1 AGRICULTURE AND THE ENVIRONMENT IN THE
HUMID TROPICS
21
The Humid Tropics 22
Forest Characteristics and Benefits 29
Conversion of Humid Tropic Forests 33
Sustainable Agriculture in the Humid Tropics 51
The Need for an Integrated Approach 62
Moving Toward Sustainability 64
2 SUSTAINABLE LAND USE OPTIONS 66
Intensive Cropping Systems 70
Shifting Cultivation 77
Agropastoral Systems 82
Cattle Ranching 85
CONTENTS xiii
Agroforestry Systems 92
Mixed Tree Systems 100
Perennial Tree Crop Plantations 110
Plantation Forestry 115
Regenerating and Secondary Forests 118
Natural Forest Management 125
Modified Forests 132
Forest Reserves 133

3 TECHNOLOGICAL IMPERATIVES FOR CHANGE 138
Knowledge About Land Use Options 139
Land Use Design and Management Considerations 145
Ecologic Guidelines for Systems Management 154
Technical Needs Common to All Land Use Options 155
Commodity-Specific Research Needs 158
4 POLICY-RELATED IMPERATIVES FOR CHANGE 159
Managing Forests and Land Resources 161
Supporting Sustainable Agriculture 173
Other Policy Areas Affecting Land Use 188
REFERENCES 192
APPENDIX: EMISSIONS OF GREENHOUSE GASES
FROM TROPICAL DEFORESTATION AND SUB-
SEQUENT USES OF THE LAND
Virginia H. Dale, Richard A. Houghton, Alan
Grainger, Ariel E. Lugo, and Sandra Brown
215
PART TWO: COUNTRY PROFILES
BRAZIL
Emanuel Adilson Souza Serrão and Alfredo Kingo
Oyama Homma
263
CÔTE D'IVOIRE
Simeon K. Ehui
352
INDONESIA
Junus Kartasubrata
393
MALAYSIA
Jeffrey R. Vincent and Yusuf Hadi

440
MEXICO
Arturo Gómez-Pompa, Andrea Kaus, Juan Jiménez-
Osornio, David Bainbridge, and Veronique M. Rorive
483
CONTENTS xiv
THE PHILIPPINES
Dennis P. Garrity, David M. Kummer, and Ernesto S.
Guiang
549
ZAIRE
Mudiayi S. Ngandu and Stephen H. Kolison, Jr.
625
GLOSSARY 659
AUTHORS 675
INDEX 679
CONTENTS xv
CONTENTS xvi
Executive Summary
Agriculture and forestry are major human activities on the global landscape.
Increasingly, data show that many widely employed agricultural and forestry
practices are having significant adverse effects on local and regional soil
conditions, water quality, biological diversity, climatic patterns, and long-term
biological and agricultural productivity. These local and regional adverse effects
are now being felt on a global scale, and have become matters of international
concern. These issues are especially acute in the world's humid tropic regions.
Timing is critical. Land transformation in northern Europe, for example,
from a natural state to its present-day highly intensive agriculture and land use,
occurred over thousands of years. Changes in the humid tropics are occurring at a
more rapid rate. Shifts in economics and population, internal and external to the

region, have ultimately yielded radical changes to the landscape, with mixed
results. Widespread, inappropriate use of fragile landscapes is also causing
significant reduction in production potential. Within one generation, in some
cases, areas will be degraded beyond economically feasible restoration.
Agricultural production practices in tropical regions are frequently
unsustainable because the capacity of land to support crop production is rapidly
exhausted. This fundamental problem is exacerbated by the pressures arising from
poverty and the demand for food. Principal factors undermining crop production
capacity include soil erosion,
EXECUTIVE SUMMARY 1
loss of soil nutrients, water management problems, and pest outbreaks, as well as
socioeconomic environments that frequently limit the use of alternative solutions
for more sustainable agricultural development. Faced with declining yields,
farmers in many areas of the humid tropics typically seek new forestlands to clear
for crop production. Unsustainable logging practices and the conversion of
environmentally fragile lands to crop production and cattle ranching pose
difficulties in achieving long-term economic development and food production
goals, and often contribute to environmental degradation.
This report focuses on the world's humid tropics. It examines the potential of
improved agricultural and land use systems to provide lasting benefits for these
regions and to alleviate adverse environmental effects at local and global levels.
In assessing agricultural sustainability, development, and resource management in
the humid tropics, the committee recognized the need for sustainable land use
systems that
• Maintain the long-term biological and ecological integrity of natural
resources,
• Provide economic returns to individual farmers and farm-related
industries,
• Contribute to the quality of life of rural populations, and
• Strengthen the economic development strategies of countries in the

humid tropics.
The committee also identified constraints to adopting sustainable land use
systems.
A key factor in attaining improved resource management, which can lead to
agricultural sustainability and development, is population. Population issues—
and the accompanying and overwhelming incidence of poverty—are critical in
many regions of the world, and certainly in the humid tropics. However, it was
not within the scope of this study to specifically analyze or draw conclusions
about data on population densities, pressure, or trends. In this report, the
committee does, however, evaluate land use options not only from a biophysical
basis, but also from social and economic bases.
FINDINGS
The committee's assessment confirms that land degradation and
deforestation are severe in many areas. But, more important, the committee has
found that farmers are employing a wide range of
EXECUTIVE SUMMARY 2
alternative strategies, albeit in limited areas, for confronting land use problems
and for moving toward sustainability. In spite of obstacles, innovative farmers,
foresters, researchers, and land managers continue to develop and refine land use
practices, many of which, if broadly implemented, will ultimately benefit
agricultural production, the economy, and the environment. With appropriate
changes in policies, research, and information and extension networks, the
committee believes the rate of progress in developing and adopting sustainable
land use systems could be accelerated.
Based on its study, the committee arrived at three major findings.
1. Throughout the humid tropics, degraded lands can be found that
have the potential to be restored. The country profiles included in
this report cite examples of successful restoration, although in many
cases, a scientific understanding and documentation of the process is
incomplete. The committee notes, however, that as researchers move

into complex, interrelated issues involving land use in the humid
tropics, some standard scientific practices such as replications,
retesting over large areas, and statistical analysis will be difficult if
not impossible. Experience and observation over time, however, will
validate the restoration methods that lead to the more sustainable
land uses. The application of restoration methods can be accelerated
along with the scientific analysis of their effectiveness.
2. A continuum of land use systems exists ranging from those that entail
minimal disturbance of natural resources to those that involve
substantial clearing of forests. Many of the successful systems
involve integrative approaches to farming and forestry that are
characterized by a high level of environmental stability, increased
productivity, and social and economic improvements, while only
modestly reducing biodiversity. A wide variety of sustainable land
use methods are available and can be adapted to the specific needs,
limitations, resource bases, and economic conditions of different land
sites. Farmers, foresters, and land managers will need to receive
information and technical assistance in developing new management
skills to select and employ sustainable land use systems.
3. Some locales of the humid tropics are successfully shifting from
economic growth that is based largely on forest harvest to a more
diversified economy involving substantial nonfarm employment.
Economic gains from further harvest of forestlands are increasingly
marginal. Development of new markets for the products of the local
farmer is often essential if necessary incentives for diversification are
to exist. Market development can be an effective means of
encouraging sustainable, diversified land use. Successful
diversification can offer increased
EXECUTIVE SUMMARY 3
employment as well as stimulate both investment in transportation,

storage, and processing and expansion of marketing and trade
opportunities. If diversification is to be attained, however, a
management systems approach is required for the research necessary
to fuel and continue development. The result can be general
economic growth that is less dependent on forest conversion.
The three findings—the potential to restore degraded lands, the range of
appropriate land uses, and the capacity for general economic growth—have
brought the committee to conclude that more effective management of forests and
other lands will be required to resolve natural resource and economic issues in the
humid tropics.
LANDSCAPE MANAGEMENT: A GLOBAL REQUIREMENT
Superficially, the underlying cause for the transformation and degradation of
the landscape in the humid tropics may appear to be excessive forest conversion,
but in reality there are many underlying causes that are interrelated and
cumulative in their effects. The committee strongly believes, however, that
optimal and balanced management of the entire landscape is integral to resolving
problems related to forest conversion, agricultural production, and land use
options in all countries of the humid tropics and in all their unique local
situations.
The committee envisions that a comprehensive development scheme could
• Provide an enabling environment for institution building, credit and
financing, and improved marketing of products;
• Increase incentives and opportunities for sustainable agricultural
practices; and
• Strengthen research, development, and dissemination.
This report is based on the committee's conclusion that it will be necessary,
within the next generation, to achieve effective management of all land resources
for sustained use. These land resources include the pristine forest, which should
be protected in perpetuity, to lands transformed into plantations or small
landholdings. Management will include decision-making at every step: by the

farmer or landholder, by the village or community, and by regional and national
agencies. Failure to implement sustainable resource management systems will
mean the loss of much of the remaining tropical forests and wetlands, the
endemic plant and animal species, and the values they represent.
Agricultural lands and forested lands are often viewed as man
EXECUTIVE SUMMARY 4
aged ecosystems. But now, with the increasing rate of change in human activity
across the face of the land, the earth itself must be viewed as a managed
ecosystem.
Timing is critical. What is not managed is at risk of being lost.
THE HUMID TROPICS
Technically, the humid tropics is a bioclimatic region of the world
characterized by consistently high temperatures, abundant precipitation, and high
relative humidity. Gradients of temperature, rainfall, soils, and slope of the land
contribute to variations in vegetation. Tropical lowland vegetation constitutes
about 80 percent of the vegetation in the humid tropics. Although a variety of
distinct plant associations and forest formations exist in the region, the forests of
the humid tropics are often referred to as tropical rain forests. Collectively,
however, lowland, premontane, and montane forest formations that include
moist, wet, and rain forests can be generally referred to as humid tropic or
tropical moist forests.
Humid tropic conditions are found over nearly 50 percent of the tropical land
mass and 20 percent of the earth's total land surface—an area of about 3 billion
ha. This total is distributed among three principal regions. Tropical Central and
South America contain about 45 percent of the world's humid tropics, Africa
about 30 percent, and Asia about 25 percent. As many as 62 countries are located
partly or entirely within the humid tropics.
Forest Conversion
Forest conversion is defined as the alteration of forest cover and forest
conditions through human intervention. Deforestation is a conversion extreme

that reduces crown cover to less than 10 percent. Available data suggest that the
annual rate of deforestation in the (primarily humid) tropics increased from 9.2
million ha per year in the late 1970s to an average of 16.8 million ha per year in
the 1980s. Deforestation currently affects about 1.2 percent of the total tropical
forest area annually. Forest degradation—changes in forest structure and function
of sufficient magnitude to have long-term negative effects on the forest's
productive potential—also affects a large area.
CAUSES OF FOREST CONVERSION
The leading direct causes of forest loss and degradation include large-scale
commercial logging and timber extraction, the advance
EXECUTIVE SUMMARY 5
ment of agricultural frontiers and subsequent use of land by subsistence farmers,
conversion of forests to perennial tree plantations and other cash crops,
conversion to commercial livestock production, land speculation, the cutting and
gathering of wood for fuel and charcoal, and large-scale colonization and
resettlement projects. The demand for land by shifting cultivators, small-scale
farmers, and landless migrants accounts for a significant portion of forest
conversion in some regions. Most of the farmers in the humid tropics, however,
are acting in response to a socioeconomic environment that offers few
alternatives.
Convoluted rows of oil palms stretch along the border of a tropical rain forest in
Malaysia. As a result of farming projects sponsored by the Malaysian
government, thousands of hectares of rain forest have been converted to
farmlands. The government's drive to reduce landlessness and unemployment
began in the 1950s. Credit: James P. Blair © 1983 National Geographic Society.
EXECUTIVE SUMMARY 6
CONSEQUENCES OF FOREST CONVERSION
Forest conversion, especially deforestation, can have far-ranging
environmental, economic, and social effects. Environmental consequences can
include the disruption of natural hydrological processes, soil erosion and

degradation, nutrient depletion, loss of biological diversity, increased
susceptibility to fires, and changes in local distribution and amount of rainfall.
The social consequences of unsustainable conversion practices may include
the decline of indigenous cultural groups and the loss of knowledge of local
resources and resource management practices; dislocation of small communities
of farmers and forest dwellers as forestlands are appropriated for more profitable
land uses; and continued poverty and rural migration as farmers abandon lands
degraded through soil-depleting agricultural practices. The economic
consequences include the loss of production potential as soil is degraded; the loss
of biological resources, such as foods or pharmaceuticals, from primary forests;
the destabilization of watersheds, with the attendant downstream effects of
flooding and siltation; and, at the global level, the long-term impacts of
deforestation on global climate change.
Agriculture in the Humid Tropics
The efficiency of tropical agriculture is determined by a combination of
environmental factors (including climate, soil, and biological conditions) and
social, cultural, and economic factors. Agricultural systems and techniques that
have evolved over time to meet the special environmental conditions of the humid
tropics include the paddy rice systems of Southeast Asia; terrace, mound, and
drained field systems; raised bed systems, such as the chinampas of Mexico and
Central America; and a variety of agroforestry, shifting cultivation, home garden,
and natural forest systems. Although diverse in their adaptations, these systems
often share many traits, such as high retention of essential nutrients, maintenance
of vegetative cover, high diversity of crops and crop varieties, complex spatial
and temporal cropping patterns, and the integration of domestic and wild animals
into the system.
Shifting cultivation is a common agricultural approach in the tropics.
Traditionally, it incorporates practices that maintain or conserve the natural
resource base, including a natural restoration or fallow cycle. Today, however,
the hallmarks of unstable shifting cultivation, or slash-and-burn agriculture, are

shortened fallow periods that lead to fertil
EXECUTIVE SUMMARY 7
ity decline, weed infestation, disruption of forest regeneration, and excessive soil
erosion.
Monocultural systems have been successfully introduced over large areas of
the humid tropics, and include production of coffee, tea, bananas, citrus fruits,
palm oil, rubber, sugarcane, and other commodities produced primarily for
export. Plantations and other monocultural systems provide employment and earn
foreign exchange.
Adopting an Integrated Approach to Land Use
The committee has focused its analysis on the relationship between forest
conversion and agriculture, and on how the problems of both might be better
addressed through developing and implementing more sustainable land use
systems. Improved land use in the humid tropics requires an approach that
recognizes the characteristic cultural and biological diversity of these lands,
incorporates ecological processes, and involves local communities at all stages of
the development process.
Fundamental scientific, social, and economic questions—and certainly the
more applied problems—are multifaceted. Steady progress toward sustainability
and the resolution of problems in the humid tropics requires that several scientific
disciplines be integrated and managed to ensure collaboration and synergy.
SUSTAINABLE LAND USE OPTIONS
No single type of land use can simultaneously meet all the requirements for
sustainability or fit the diverse socioeconomic and ecological conditions. In this
report, the committee describes 12 overlapping categories within the complete
range of sustainable land use options. The committee also presents a scheme, for
comparing the attributes of each of the 12 categories (see Chapter 3), that can be
used as a tool for management and decision making in evaluating land use
options for a specific area. The attributes are grouped as biophysical, economic,
and social benefits. With proper management, these land use options have the

potential to stabilize forest buffer zone areas, reclaim cleared lands, restore
degraded and abandoned lands, improve small farm productivity, and provide
rural employment. They are described below:
• Intensive cropping systems are concentrated on lands with adequate
water, naturally fertile soils, low to modest slope, and other
environmental characteristics conducive to high agricultural
productivity. The best agricultural lands in most parts of the humid
tropics
EXECUTIVE SUMMARY 8
have been cleared and converted to high-productivity agriculture. High-
productivity technologies, if improperly applied, can lead to resource
degradation through, for example, nutrient loading from fertilizers,
water contamination from pesticides and herbicides, and waterlogging
and salinization of land. Food needs require that these systems remain
productive and possibly expand in area, but that they be stabilized
through biological pest management, nutrient containment, and
improved water management.
• Shifting cultivation systems are traditional and remain in widespread use
throughout the humid tropics. Temporary forest clearings are planted for
a few years with annual or short-term perennial crops, and then allowed
to remain fallow for a longer period than they were cropped. Migration
has brought intensified shifting cultivation to newly cleared lands, where
it is often inappropriate. In these areas, however, shifting cultivation can
be stabilized by adopting local cropping practices and varieties,
observing sufficient fallow periods, maintaining continuous ground
cover, diversifying cropping systems, and introducing fertility-restoring
plants and mulches into natural fallows.
• Agropastoral systems combine crop and animal production, allowing for
enhanced agroecosystem productivity and stability through efficient
nutrient management, integrated management of soil and water

resources, and a wider variety of both crop and livestock products.
Agropastoral systems may provide relatively high levels of income and
employment in resource-poor areas.
• Cattle ranching on a large scale has been identified as a leading
contributor to deforestation and environmental degradation in the humid
tropics, primarily in Latin America and some Asian countries. However,
cattle ranching operations can be made more sustainable by reclaiming
degraded pastures in deforested lands through the use of improved
forages, fertilization, weed control, and appropriate mechanization, and
by integrating pasture-based production systems with agroforestry and
annual crop systems. Medium- to small-scale ranching systems have
proved economical, but require changes in land tenure and ownership
incentives.
• Agroforestry systems include a range of options in which woody and
herbaceous perennials are grown on land that also supports agricultural
crops, animals, or both. Under ideal conditions, these systems offer
multiple agronomic, environmental, and socioeconomic benefits for
resource-poor small-scale farmers, including enhanced nutrient cycling,
fixing of atmospheric nitrogen through the use of perennial legumes,
efficient allocation of water and light, conservation of soils, natural
suppression of weeds, and diversification of farm products. Agroforestry
systems require market access for widespread use.
EXECUTIVE SUMMARY 9