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

Sustainable Agriculture and the Environment inthe Committee on Sustainable Agriculture and the Environment in the Humid Tropics Board on Agriculture and Board on Science and Technology f

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

HUMID TROPICS

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 tainable Agriculture and the Environment in the Humid Tropics, Board on Agriculture and Board on Science and Technology for International Development, National Research Council.

Sus-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 RicoALISON 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 EasternAmazon, 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

BOARD ON AGRICULTURE

THEODORE L HULLAR, Chair, University of California, Davis

PHILIP H ABELSON, American Association for the Advancement of ScienceDALE E BAUMAN, Cornell University

R JAMES COOK, Agricultural Research Service at Washington State UniversityELLIS 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

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

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

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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 jointly by both Academies and the Institute of Medicine Dr Frank Press and

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The increasingly adverse effects of human activities on the earth's land,water, atmospheric, and biotic resources have clearly demonstrated that a newattitude of stewardship and sustainable management is required if our globalresources are to be conserved and remain productive Nowhere is this need moreurgent than in the world's humid tropics Its populations, many subsisting at orbelow the poverty level, will continue to rely on the resource base to meet theirneeds That base must be stabilized while becoming increasingly productive.Thoughtful and prompt actions, especially positive policy changes, are required tobreak the current pattern of unplanned deforestation in the humid tropics, toreverse environmental degradation caused by improper or mismanaged crop andanimal 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 Scienceand Technology for International Development convened the 15-memberCommittee on Sustainable Agriculture and the Environment in the HumidTropics 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 systemsthat (1) maintain the long-term biological and ecological integrity of naturalresources, (2) provide economic returns at the farm level, (3) contribute to quality

of life of rural populations, and

(4) integrate into national economic development strategies In particular, thecommittee was asked to identify and analyze key problems of agriculturalpractices that contribute to environmental degradation and result in decliningagricultural production in humid tropic environments.

The committee began its work in March 1990 It sought to understand theoverarching environmental, social, and policy contexts of land conversion anddeforestation—and the promise of sustainable land uses—by integrating theviews 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 forestboundary, an area where agriculture and forestry merge in a continuum ofproduction types involving trees, agricultural crops, and animals The committeeaddressed intensive, high-input agriculture only as it relates to commonenvironmental problems The committee undertook supplemental analyses oftropical forest land use policies and the effects of tropical land use on globalclimate change We sought a wide range of scientific data, specializedinformation, and expert views to address our broad charge

A critical component of the humid tropics equation that was not within thescope of the study is human population The committee acknowledges populationdynamics as a major factor in achieving sustainable land use and development inthe humid tropics; the land use systems it describes fit a broad range ofpopulation densities We stress the importance of population issues, particularly

in this region of the world, but an analysis of population densities, pressures, andtrends was not part of our study, nor does the composition of the committeereflect 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 Eachland use option would take advantage of the opportunities inherent in physicalresource patterns, labor, market availability, and social setting, and each wouldcontribute to the common goal of sustainability in the humid tropics

The land use options scheme in Chapter 2 and its accompanying table forevaluating land use attributes can be used as a guide in decision making Thepresentation makes the information usable by in-country decision makers, fromthe 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

Part One is the committee's deliberative report It emphasizes the restoration

of degraded land, the importance of general economic growth as an alternative toforest exploitation, and the need for comprehensive management of forest andagricultural resources The underlying premise of the committee's work is thatunder conditions of economic and social pressure, what is not managed today is

at risk of being lost tomorrow

committee and presents key recommendations Chapter 1 describes the humidtropics, the consequences of forest conversion and deforestation, environmentalfactors affecting agriculture, and the fostering of sustainable land use in thehumid tropics Chapter 2 discusses major land use options that local, regional, andnational managers might choose in making decisions to achieve food productiongoals, maintain or increase local income levels, and protect the natural resourcebase Chapter 3 discusses technical research needs and presents recommendations

on land use options Chapter 4 presents policy imperatives to promotesustainability The Appendix to Part One presents a discussion of emissions ofgreenhouse gases associated with land use change

To enhance its understanding, the committee commissioned a series ofcountry profiles to gather information on land use and forest conversion indifferent countries, to evaluate general causes and consequences within specificcontexts, to identify sustainable land use alternatives, and to compare policyimplications Seven country profiles are presented in Part Two Authors reviewagricultural 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 aboutthe potential benefits of sustainable agriculture in the humid tropics, rather than tocondemn the forces that have contributed to the current situation It is an attempt

to promote the restoration and rehabilitation of already deforested lands, toincrease their productivity, and to explore the policy changes required to take thenext steps toward sustainability Guidelines for future research and policy,whether for conserving natural ecosystems or for encouraging sustainableagroecosystems, must be designed with a global perspective and within thecontext of each country's environment, history, and culture

The committee underscores the fact that sustainable agriculture in any givencountry will consist of many diverse production systems, each fitting specificenvironmental, social, and market niches Some alternatives require higherinputs, labor, or capital—depending

on their makeup, resource base, and environment—but each must become moresustainable Conversely, each system can contribute toward the sustainability ofthe agricultural system in general by helping to meet the varied and changingneeds facing countries in the humid tropics To maintain a diversity ofapproaches while making real progress toward common goals is the challengethat confronts all who are concerned with the future of the lands and people of thehumid tropics.

RICHARD R HARWOOD, Chair

Committee on Sustainable

Agriculture and the Environment in the Humid Tropics

The disciplines, multidisciplinary experiences, expertise, and countries ofthe world that are represented by the many individuals who have generouslycontributed to this report constitute a very long list Because of the efforts of themany who shared ideas and offered background knowledge, the committee wasable to expand its views of issues relating to sustainable agriculture and theenvironment in the humid tropics and benefit from a variety of perspectives.Among the many individuals whose work was of special significance to thisreport are the authors of the appended paper, the country profiles, and theircollaborators The descriptive data and analyses presented in the seven countryprofiles, contained in Part Two of the report, provided much of the foundation forthe committee's work In addition to the authors and their collaborators, thecommittee acknowledges the contributions of Cyril B Brown, PurdueUniversity; Avtar Kaul, Winrock International; Daniel Nepstad, Woods HoleResearch Center; and Christopher Uhl, Pennsylvania State University (BothNepstad and Uhl are associated with the Center for Agroforestry Research of theEastern Amazon, Belém, Brazil.) Michael Hayes provided valuable editorialassistance in preparing the country profiles for publication

To broaden its information resources, the committee convened two regionalmeetings on agricultural and environmental practices and policies in the humidtropics The first meeting was held at the

Faculty of Agronomy, University of Costa Rica, in San Jose The second washeld in Bangkok, Thailand, under the auspices of the Asian Regional Office ofthe National Research Council.

During the course of its deliberations, the committee sought the counsel andadvice of independent scholars and individuals representing a range oforganizations Among those who gave generously of their experience wereRobert O Blake, Committee on Agricultural Sustainability for DevelopingCountries; Erick Fernandes, Thurman Grove, and Cheryl Palm, North CarolinaState University; Douglas Lathwell, Cornell University; Charles H Murray, Foodand 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 onInternational Agricultural Research The assistance of Andrea Kaus andVeronique M Rorive, University of California at Riverside, was also helpful tothe committee

Research assistance was provided by three student interns, who weresponsored by the Midwest Universities Consortium for International Activities,Inc The committee extends special thanks to Joi Brooks, University of Illinois atUrbana, and Jil Reifschneider and Kristine Agard, University of Wisconsin.The committee is grateful to Curt Meine and Barbara Rice, whose skill andteamwork transformed imperfect and incomplete draft materials into acomprehensive report We are particularly grateful to Jay Davenport, whoseinsights and support were invaluable to the committee throughout the course ofthe study

And the committee especially recognizes the efforts of Pedro Sanchez, whoserved as committee chairman until assuming responsibilities as director general

of the International Center for Research in Agroforestry, Nairobi, Kenya

Contents

Agroforestry Systems 92

APPENDIX: EMISSIONS OF GREENHOUSE GASES

FROM TROPICAL DEFORESTATION AND SEQUENT USES OF THE LAND

SUB-Virginia H Dale, Richard A Houghton, Alan Grainger, Ariel E Lugo, and Sandra Brown

Junus Kartasubrata

393MALAYSIA

Jeffrey R Vincent and Yusuf Hadi

440MEXICO

Arturo Gómez-Pompa, Andrea Kaus, Juan Osornio, David Bainbridge, and Veronique M Rorive

Jiménez-483

Executive Summary

Agriculture and forestry are major human activities on the global landscape.Increasingly, data show that many widely employed agricultural and forestrypractices are having significant adverse effects on local and regional soilconditions, water quality, biological diversity, climatic patterns, and long-termbiological and agricultural productivity These local and regional adverse effectsare now being felt on a global scale, and have become matters of internationalconcern 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 amore rapid rate Shifts in economics and population, internal and external to theregion, have ultimately yielded radical changes to the landscape, with mixedresults Widespread, inappropriate use of fragile landscapes is also causingsignificant reduction in production potential Within one generation, in somecases, areas will be degraded beyond economically feasible restoration

Agricultural production practices in tropical regions are frequentlyunsustainable because the capacity of land to support crop production is rapidlyexhausted This fundamental problem is exacerbated by the pressures arising frompoverty and the demand for food Principal factors undermining crop productioncapacity include soil erosion,

loss of soil nutrients, water management problems, and pest outbreaks, as well associoeconomic environments that frequently limit the use of alternative solutionsfor more sustainable agricultural development Faced with declining yields,farmers in many areas of the humid tropics typically seek new forestlands to clearfor crop production Unsustainable logging practices and the conversion ofenvironmentally fragile lands to crop production and cattle ranching posedifficulties in achieving long-term economic development and food productiongoals, and often contribute to environmental degradation.

This report focuses on the world's humid tropics It examines the potential ofimproved agricultural and land use systems to provide lasting benefits for theseregions and to alleviate adverse environmental effects at local and global levels

In assessing agricultural sustainability, development, and resource management inthe humid tropics, the committee recognized the need for sustainable land usesystems that

• Maintain the long-term biological and ecological integrity of naturalresources,

industries,

• Contribute to the quality of life of rural populations, and

• Strengthen the economic development strategies of countries in thehumid tropics

The committee also identified constraints to adopting sustainable land usesystems

A key factor in attaining improved resource management, which can lead toagricultural sustainability and development, is population Population issues—and the accompanying and overwhelming incidence of poverty—are critical inmany regions of the world, and certainly in the humid tropics However, it wasnot within the scope of this study to specifically analyze or draw conclusionsabout data on population densities, pressure, or trends In this report, thecommittee does, however, evaluate land use options not only from a biophysicalbasis, but also from social and economic bases

FINDINGS

The committee's assessment confirms that land degradation anddeforestation are severe in many areas But, more important, the committee hasfound that farmers are employing a wide range of

alternative strategies, albeit in limited areas, for confronting land use problemsand for moving toward sustainability In spite of obstacles, innovative farmers,foresters, researchers, and land managers continue to develop and refine land usepractices, many of which, if broadly implemented, will ultimately benefitagricultural production, the economy, and the environment With appropriatechanges in policies, research, and information and extension networks, thecommittee believes the rate of progress in developing and adopting sustainableland 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 manycases, a scientific understanding and documentation of the process isincomplete The committee notes, however, that as researchers moveinto complex, interrelated issues involving land use in the humidtropics, some standard scientific practices such as replications,retesting over large areas, and statistical analysis will be difficult ifnot impossible Experience and observation over time, however, willvalidate the restoration methods that lead to the more sustainableland uses The application of restoration methods can be acceleratedalong 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 arecharacterized by a high level of environmental stability, increasedproductivity, and social and economic improvements, while onlymodestly reducing biodiversity A wide variety of sustainable landuse methods are available and can be adapted to the specific needs,limitations, resource bases, and economic conditions of different landsites Farmers, foresters, and land managers will need to receiveinformation and technical assistance in developing new managementskills 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 increasinglymarginal Development of new markets for the products of the localfarmer is often essential if necessary incentives for diversification are

to exist Market development can be an effective means ofencouraging sustainable, diversified land use Successfuldiversification can offer increased

employment as well as stimulate both investment in transportation,storage, and processing and expansion of marketing and tradeopportunities If diversification is to be attained, however, amanagement systems approach is required for the research necessary

to fuel and continue development The result can be generaleconomic growth that is less dependent on forest conversion

The three findings—the potential to restore degraded lands, the range ofappropriate land uses, and the capacity for general economic growth—havebrought the committee to conclude that more effective management of forests andother lands will be required to resolve natural resource and economic issues in thehumid tropics

LANDSCAPE MANAGEMENT: A GLOBAL REQUIREMENT

Superficially, the underlying cause for the transformation and degradation ofthe landscape in the humid tropics may appear to be excessive forest conversion,but in reality there are many underlying causes that are interrelated andcumulative in their effects The committee strongly believes, however, thatoptimal and balanced management of the entire landscape is integral to resolvingproblems related to forest conversion, agricultural production, and land useoptions in all countries of the humid tropics and in all their unique localsituations

The committee envisions that a comprehensive development scheme could

• Provide an enabling environment for institution building, credit andfinancing, and improved marketing of products;

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 resourcesfor sustained use These land resources include the pristine forest, which should

be protected in perpetuity, to lands transformed into plantations or smalllandholdings Management will include decision-making at every step: by thefarmer or landholder, by the village or community, and by regional and nationalagencies Failure to implement sustainable resource management systems willmean the loss of much of the remaining tropical forests and wetlands, theendemic plant and animal species, and the values they represent

Agricultural lands and forested lands are often viewed as man

aged ecosystems But now, with the increasing rate of change in human activityacross the face of the land, the earth itself must be viewed as a managedecosystem.

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 worldcharacterized by consistently high temperatures, abundant precipitation, and highrelative humidity Gradients of temperature, rainfall, soils, and slope of the landcontribute to variations in vegetation Tropical lowland vegetation constitutesabout 80 percent of the vegetation in the humid tropics Although a variety ofdistinct plant associations and forest formations exist in the region, the forests ofthe humid tropics are often referred to as tropical rain forests Collectively,however, lowland, premontane, and montane forest formations that includemoist, wet, and rain forests can be generally referred to as humid tropic ortropical moist forests

Humid tropic conditions are found over nearly 50 percent of the tropical landmass 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 andSouth America contain about 45 percent of the world's humid tropics, Africaabout 30 percent, and Asia about 25 percent As many as 62 countries are locatedpartly or entirely within the humid tropics

Forest Conversion

Forest conversion is defined as the alteration of forest cover and forestconditions through human intervention Deforestation is a conversion extremethat reduces crown cover to less than 10 percent Available data suggest that theannual rate of deforestation in the (primarily humid) tropics increased from 9.2million ha per year in the late 1970s to an average of 16.8 million ha per year inthe 1980s Deforestation currently affects about 1.2 percent of the total tropicalforest area annually Forest degradation—changes in forest structure and function

of sufficient magnitude to have long-term negative effects on the forest'sproductive potential—also affects a large area

CAUSES OF FOREST CONVERSION

The leading direct causes of forest loss and degradation include large-scalecommercial logging and timber extraction, the advance

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 andgathering of wood for fuel and charcoal, and large-scale colonization andresettlement projects The demand for land by shifting cultivators, small-scalefarmers, and landless migrants accounts for a significant portion of forestconversion in some regions Most of the farmers in the humid tropics, however,are acting in response to a socioeconomic environment that offers fewalternatives.

Convoluted rows of oil palms stretch along the border of a tropical rain forest inMalaysia 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 unemploymentbegan in the 1950s Credit: James P Blair © 1983 National Geographic Society

CONSEQUENCES OF FOREST CONVERSION

Forest conversion, especially deforestation, can have far-rangingenvironmental, economic, and social effects Environmental consequences caninclude the disruption of natural hydrological processes, soil erosion anddegradation, nutrient depletion, loss of biological diversity, increasedsusceptibility to fires, and changes in local distribution and amount of rainfall.The social consequences of unsustainable conversion practices may includethe decline of indigenous cultural groups and the loss of knowledge of localresources and resource management practices; dislocation of small communities

of farmers and forest dwellers as forestlands are appropriated for more profitableland uses; and continued poverty and rural migration as farmers abandon landsdegraded through soil-depleting agricultural practices The economicconsequences 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 offlooding and siltation; and, at the global level, the long-term impacts ofdeforestation on global climate change

Agriculture in the Humid Tropics

The efficiency of tropical agriculture is determined by a combination ofenvironmental factors (including climate, soil, and biological conditions) andsocial, cultural, and economic factors Agricultural systems and techniques thathave evolved over time to meet the special environmental conditions of the humidtropics 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 systemsoften share many traits, such as high retention of essential nutrients, maintenance

of vegetative cover, high diversity of crops and crop varieties, complex spatialand temporal cropping patterns, and the integration of domestic and wild animalsinto the system

Shifting cultivation is a common agricultural approach in the tropics.Traditionally, it incorporates practices that maintain or conserve the naturalresource base, including a natural restoration or fallow cycle Today, however,the hallmarks of unstable shifting cultivation, or slash-and-burn agriculture, areshortened fallow periods that lead to fertil

ity decline, weed infestation, disruption of forest regeneration, and excessive soilerosion.

Monocultural systems have been successfully introduced over large areas ofthe humid tropics, and include production of coffee, tea, bananas, citrus fruits,palm oil, rubber, sugarcane, and other commodities produced primarily forexport Plantations and other monocultural systems provide employment and earnforeign exchange

Adopting an Integrated Approach to Land Use

The committee has focused its analysis on the relationship between forestconversion and agriculture, and on how the problems of both might be betteraddressed through developing and implementing more sustainable land usesystems Improved land use in the humid tropics requires an approach thatrecognizes the characteristic cultural and biological diversity of these lands,incorporates ecological processes, and involves local communities at all stages ofthe development process

Fundamental scientific, social, and economic questions—and certainly themore applied problems—are multifaceted Steady progress toward sustainabilityand the resolution of problems in the humid tropics requires that several scientificdisciplines 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 forsustainability or fit the diverse socioeconomic and ecological conditions In thisreport, the committee describes 12 overlapping categories within the completerange of sustainable land use options The committee also presents a scheme, forcomparing the attributes of each of the 12 categories (see Chapter 3), that can beused as a tool for management and decision making in evaluating land useoptions for a specific area The attributes are grouped as biophysical, economic,and social benefits With proper management, these land use options have thepotential to stabilize forest buffer zone areas, reclaim cleared lands, restoredegraded and abandoned lands, improve small farm productivity, and providerural employment They are described below:

• Intensive cropping systems are concentrated on lands with adequate

water, naturally fertile soils, low to modest slope, and otherenvironmental characteristics conducive to high agriculturalproductivity The best agricultural lands in most parts of the humidtropics

have been cleared and converted to high-productivity agriculture productivity technologies, if improperly applied, can lead to resourcedegradation through, for example, nutrient loading from fertilizers,water contamination from pesticides and herbicides, and waterloggingand salinization of land Food needs require that these systems remainproductive and possibly expand in area, but that they be stabilizedthrough biological pest management, nutrient containment, andimproved water management.

High-• 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 Migrationhas 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 groundcover, diversifying cropping systems, and introducing fertility-restoringplants and mulches into natural fallows

• Agropastoral systems combine crop and animal production, allowing for

enhanced agroecosystem productivity and stability through efficientnutrient management, integrated management of soil and waterresources, and a wider variety of both crop and livestock products.Agropastoral systems may provide relatively high levels of income andemployment in resource-poor areas

• Cattle ranching on a large scale has been identified as a leading

contributor to deforestation and environmental degradation in the humidtropics, primarily in Latin America and some Asian countries However,cattle ranching operations can be made more sustainable by reclaimingdegraded pastures in deforested lands through the use of improvedforages, fertilization, weed control, and appropriate mechanization, and

by integrating pasture-based production systems with agroforestry andannual crop systems Medium- to small-scale ranching systems haveproved economical, but require changes in land tenure and ownershipincentives

• Agroforestry systems include a range of options in which woody and

herbaceous perennials are grown on land that also supports agriculturalcrops, animals, or both Under ideal conditions, these systems offermultiple agronomic, environmental, and socioeconomic benefits forresource-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, naturalsuppression of weeds, and diversification of farm products Agroforestrysystems require market access for widespread use

• Mixed tree systems are common throughout the humid tropics In

contrast to modern plantations, in which one tree species is grown toyield a single commercial product, mixed tree systems employ a variety

of useful species, planted together, to yield different products (includingfruits, forage, fiber, and medicines) These systems also protect soil andwater resources, provide pest control, serve as habitat for game andother animal species, and offer opportunities for small-scale reforestationefforts that are economically productive and environmentally sound

• Perennial tree crop plantations are part of a broad category of plantation

agriculture that includes short rotation crops (such as sugarcane andpineapple) as well as tree crops Large areas of primary forest have beenconverted to tree crop plantations Despite social and environmentalproblems inherent in these systems, modifications to enhance theirsustainability could allow plantation crops to play a role in convertingdeforested or degraded land to more ecologically and economicallysustainable use

• Plantation forestry systems in the tropics cover about 11 million ha of

land Most have been established only in the past 30 years, usually indeforested or degraded lands, primarily for fuelwood, pulpwood, andlumber production, and for environmental protection Increasingly,however, attention is focusing on the ability of plantations to accumulatebiomass, sequester atmospheric carbon, and rehabilitate damaged lands.Because these systems offer flexibility in design and purpose, theyprovide a potentially important tool for land managers in the humidtropics

• Regenerating and secondary forests have followed forest conversion and

land abandonment in many areas of the humid tropics Regeneratingforests can be viewed as a type of land use in that they provide valuablegoods and services to society, while preparing degraded lands forconversion to more intensive agricultural uses or alternative purposes.The regeneration process protects soils from erosion, restores thecapacity of the land to retain rainfall, sequesters atmospheric carbon, andallows biological diversity to increase This process can be guided andaccelerated through fire protection, supplemental planting, and othermanagement methods Regenerating forests will, if other options are notimplemented, mature into secondary forests, providing many ecologicaland economic benefits and preparing the way for the restoration ofprimary forest Properly managed secondary forests, by supplying avariety of products, increasing site fertility, and restoring biologicaldiversity, can be critical for attaining the goals of sustainability

• Natural forest management systems show promise for ameliorating the

effects of destructive logging practices The ecological characteristics,biological diversity, and structural complexity of moist tropical forestecosystems make them more vulnerable than temperate forests to theimpacts of conventional intensive forest management techniques.Management techniques (for example, selective cutting procedures) thatare more appropriate to tropical systems may provide sustainablealternatives to destructive logging and other more intensive land uses

• Modified forests are often difficult, if not impossible, to distinguish from

pristine primary forests In these areas, indigenous people have subtlyaltered the native plant and animal community, but without significantlyaffecting the rate of primary productivity, the efficiency of nutrientcycling, or other ecosystem functions Modified forests should beconsidered a viable land use that allows indigenous peoples and localcommunities to sustain their ways of life while protecting large areas offorestland

• Forest reserves have been established through a variety of protection

mechanisms, including biological and extractive reserves, wildlifepreserves, national parks, national forests, refuges, private land trusts,crown lands, and sanctuaries Reserves allow for the protection ofecosystem functions, environmental services, cultural values, andbiological diversity, and provide important opportunities for research,education, recreation, and tourism

The continuum of options from intensive cropping systems to forest reservesconstitutes a spectrum of potential land uses They meet different goals andinvolve varying degrees of forest conversion, management skill, and investment.Each confers a mix of biophysical, economic, and social benefits Consequently,trade-offs are involved in choosing among them Agroforestry systems, forexample, require fewer purchased inputs (although initial soil fertility treatmentsmay be required on degraded lands), but they generally do not generate the highlevels of employment or income on a per unit area basis that intensive crop oranimal agriculture does They are, however, adapted to less fertile soils.Perennial tree plantations, such as for oil palm or rubber, require considerablechemical inputs and labor to maintain productivity, but generate moreemployment and income on a per unit area basis than do agroforestry systems.Sustainability, in this context, largely entails meeting unique needs, minimizingnegative effects, and offering a range of opportunities for land areas that vary insize from the local farmer's field to the surrounding landscape to the country as awhole

In the Amazon River Basin in Brazil, tropical rain forest is burned to prepare theland for cattle pastures and other agricultural uses Credit: James P Blair © 1983National Geographic Society.

RECOMMENDATIONS

Progress toward sustainability in the humid tropics depends not only on theavailability of improved techniques of land use, but on the creation of a morefavorable environment for their development, dissemination, andimplementation For this to happen, substantial changes will need to take place inthe national and international institutions that determine the character of publicpolicy The committee's recommendations fall into the categories of technicalresearch needs and policy strategies

Technical Research Needs

The committee has found that publicly supported development efforts areconfined to a range of land use choices that is too narrow In this report, thecommittee identifies sustainable land use options suitable for a broad range ofconditions in the humid tropics That so many instances of diverse productionsystems were found is not sur

prising; that they appear to have such broad applicability across the humid tropics

is of great development interest

Recommendations on technical research needs are based on the success ofland uses that are chronicled in the country profiles (see Part Two, this volume)and on the potential that exists in many locales throughout the humid tropics

DOCUMENTATION OF LAND USE SYSTEMS

To be readily usable by development planners, land use systems should be defined according to their environmental, social, and economic attributes, and described in detail The place and role for each system, which will depend on the level of national or local development, should be identified along with conditions required for their implementation and evolution.

In Chapter 3, the committee provides a scheme for comparing thebiophysical, social, and economic attributes of land use systems Biophysicalattributes are grouped as nutrient cycling capacity, soil and water conservationcapacity, stability toward pests and diseases, biodiversity level, and carbonstorage Social attributes are grouped as health and nutritional benefits, culturaland communal viability, and political acceptability Economic attributes aregrouped as level of external inputs necessary to maintain optimal production,employment per land unit, and income generated

In all attribute categories, intensive cropping, agroforestry, agropastoralsystems, mixed tree plantations, and, to some extent, modified forests offersignificant benefits For many low resource areas, the newly researched anddemonstrated technologies for mixed cropping systems show considerablepromise In general, changes in social and economic attributes will be gradual

collaborative relationships between researchers and indigenous people, andproviding the groundwork for successful local development projects Sustainablesystems will often combine traditional practices and structure with more modern,scientifically derived technologies.

MONITORING

Resources should be available for linking national monitoring agencies with global satellite-based data sources so these agencies can refine, update, and verify their data bases for tracking land use changes and effects.

Monitoring systems and methodologies must be improved to trace land usechanges and their effects Only within the past 2 decades in the United States hassatellite-generated information made it possible to estimate the magnitude of soilloss and its effect on productivity In most countries of the humid tropics, onlyrudimentary data are available on soil loss, groundwater contamination,salinization, sedimentation rates, levels of biological diversity, and greenhousegas emissions Modern-day international data bases employing satellitegeneratedinformation should be more effectively linked with national monitoring systems

Policy Strategies

The goal of the committee's policy-related recommendations is to meethuman needs without further undermining the long-term integrity of tropicalsoils, waters, plants, and animals Sustainable agriculture will not automaticallyslow forest conversion, or deforestation, in the humid tropics However, thecombination of forest management and the use of sustainable land use optionswill provide a framework that each country can use to fit its capabilities, naturalresources, and stage of economic and technological development

POLICY REVIEWS

Policy reviews under way at local, national, and international levels must be broadened to consider the negative effects that policies have had on sustainable land use.

Many international and bilateral development agencies have reassessed theirforest policies in response to escalating rates of deforestation Few, however,focus on the need for agricultural sustainability At national and regional levels,policy reviews should respond to the specific biophysical, social, and economiccircumstances that affect land use patterns within countries and regions At theinternational

level, the review process will vary from institution to institution, depending on itssize and objectives and the range of its activities.

In general, policy reviews should involve multidisciplinary teams; evaluateexternalized costs of policies that encourage large-scale land clearing; assignvalue to the forests in standard economic terms; integrate forest and agriculturesectors; and integrate infrastructure, land use, and development policies

GLOBAL EQUITY

The adoption of sustainable agriculture and land use practices in the humid tropics should be encouraged through the equitable distribution of costs on a global scale.

Industrialized countries have a responsibility to assume some proportionateshare of the costs related to the adoption of sustainable land use practices Theymust use their financial and institutional resources to encourage the conservation

of natural resources and the development of human resources in developingcountries Global distribution of costs can be directed through technicalassistance, research, and institution building; financing; and international tradereforms In other words, if industrialized countries want developing countries topreserve their resources for global benefit, financial and other assistance must betransferred to developing countries specifically to protect global commonresources Assistance could be provided for in situ protection of geneticresources, enhancement of the capacity to sequester carbon, and new markets forhigh-value products of the humid tropics

Supporting Sustainable Agriculture

Changes in policies that contribute to forest conversion, deforestation, andnatural resource degradation in the humid tropics alone will not encourage theadoption of sustainable agricultural systems The committee makes the followingrecommendations for efforts to support sustainable agriculture

CREATION OF AN ENABLING ENVIRONMENT

National governments in the humid tropics should promote policies that provide an enabling environment for developing land use systems that simultaneously address social and economic pressures and environmental concerns.

Based on studies of successful experience in moving toward sus

tainable agricultural practices, the committee concluded that essentialcomponents of an enabling environment include assurance of resource accessthrough land titling or other tenure-related instruments, access to credit,investment in infrastructure, local community empowerment in the decision-making process, and social stability and security.

More than any other factor, the status of land tenure determines the destiny

of land and forest resources in the humid tropics Land tenure arrangements thatprovide long-term access to land resources are the prerequisite to efficient landuse decision making and to the implementation of sustainable land use systems.Formalization of property rights is important in many countries

INCENTIVES

National governments in the humid tropics and international aid agencies should develop and provide incentives to encourage long-term investment in increasing the production potential of degraded lands, for settling and restoring abandoned lands, and for creating market opportunities for the variety of products available through sustainable land use.

To attain the most efficient use of limited funds, it will be necessary todetermine where natural regeneration of degraded lands is proceeding withoutmajor investment, and alternatively, where regeneration and economicdevelopment will require a financial boost As regeneration and economicdevelopment proceeds, the mix of land use inputs is likely to change and so toowill the mix of appropriate incentives For example, labor-intensive agroforestrysystems that might be suitable in low-wage countries may be less financiallyviable in high-wage countries

In the case of abandoned lands, securing tenure is a critical step inrehabilitation, but special concessions may be necessary to attract farmers tothese areas Depending on local tenure arrangements, villages and communities,rather than individuals, might more appropriately be the recipient of subsidies, taxconcessions, and other incentives where, for example, the stabilization of entirewatersheds is critical

PARTNERSHIPS

New partnerships must be formed among farmers, the private sector, nongovernmental organizations, and public institutions to address the broad needs for research and development and the needs for knowledge transfer of the more complex, integrated land use systems.

The international community has given substantial support for research toincrease the productivity of major crops such as rice and maize, and for research

on tropical soils, livestock, chemical methods of pest control, and humannutrition Additional support will be necessary in the areas of small-landholderagroforestry systems, tree crops, improved fallow and pasture management, lowinput cropping, corridor systems, methods of integrated pest management, andother agricultural systems and technologies appropriate to higher risk lands.National and international development agencies should foster theproductive involvement of local nongovernmental organizations (NGOs) asintermediaries between themselves, national government agencies, universities,and local communities in support of the methods and goals of sustainable landuse In particular, NGOs can assume a prominent role in training and education atthe community level, in partnership with (or in the absence of) official extensionservices Local NGOs are likely to be more effective than external organizations

in shaping environmentally and socially acceptable land use policies based onlocal needs and priorities

—the nations of the humid tropics stand to gain little from the further depletion

of forests and land resources Likewise, nations beyond the humid tropics willreap few benefits by contributing to the forces behind accelerated forestconversion and deforestation

Decisions will continue to be made, necessarily in the absence of completedata But the committee strongly believes that the continuum of land use optionspresented in this report and the accompanying evaluation of attributes can provide

a foundation for decision making and the management of all lands—the key tosustainability in the humid tropics

PART ONE

1 Agriculture and the Environment in the

Humid Tropics

The wide belt of land and water that lies between the tropics of Cancer andCapricorn is home to half of the world's people and some of its most diverse andproductive ecosystems Citizens and governments within and beyond the tropicsare increasingly aware of this region's unique properties, problems, and potential

As scientific understanding of tropical ecosystems has expanded, appreciation oftheir biological diversity and the vital role they play in the functioning of theearth's biophysical systems has risen The fate of tropical rain forests, inparticular, has come to signify growing scientific and public interest in theimpact of human activities on the global environment

At the same time, the people and nations of the tropics face a difficultfuture Most of the world's developing countries are in the tropics, whereagriculture is important to rural and national economies About 60 percent of thepeople in these countries are rural residents, and a large proportion of these aresmall-scale farmers and herders with limited incomes (Population ReferenceBureau, 1991) The need to stimulate economic growth, reduce poverty, andincrease agricultural production to feed a rapidly growing population is placingmore pressures on the natural resource base in developing countries (see Part Two,this volume) The deterioration of natural resources, in turn, impedes efforts toimprove living conditions This dilemma, however, has stimulated a growingcommitment to sustain

able development among tropical and nontropical countries alike, with specialconcern for the world's humid tropics.

This report focuses on the humid tropics, a biogeographical area within thetropical zone that contains most of its population and biologically rich naturalresources The problems associated with unstable shifting cultivation and tropicalmonocultures, together with the need to improve productivity on degraded andresource-poor lands, have prompted farmers, researchers, and agriculturaldevelopment officials to search for more sustainable agricultural and land usesystems suitable for the humid tropics This chapter describes the agriculturalresources of the humid tropics, outlines the processes of forest conversion thathave affected wide areas, and examines the potential of improved agriculturalpractices to prevent continued resource degradation It stresses the need for amore integrated approach to research, policy, and development activities inmanaging resources on a more sustainable basis

The definition of agricultural sustainability varies by individual, discipline,profession, and area of concern Common characteristics include the following:long-term maintenance of natural resources and agricultural productivity;minimal adverse environmental impacts; adequate economic returns to farmers;optimal production with purchased inputs used only to supplement naturalprocesses that are carefully managed; satisfaction of human needs for food,nutrition, and shelter; and provision for the social needs of health, welfare, andsocial equity of farm families and communities All definitions embraceenvironmental, economic, and social goals in their efforts to clarify and interpretthe meaning of sustainability In addition, they suggest that farmers and farmsystems must be able to respond effectively to environmental and economicstresses and opportunities In the humid tropics, priority must be given to soilprotection and the efficient recycling of nutrients (including those derived fromexternal sources); to implementation of mixed forest and crop systems; and tosecondary forest management that incorporates forest fallow practices (Ewel,1986; Hart, 1980)

THE HUMID TROPICS

The humid tropics are defined by bioclimates that are characterized byconsistently high temperatures; abundant, at times seasonal, precipitation; andhigh relative humidity (Lugo and Brown, 1991) Annual precipitation exceeds orequals the potential return of moisture to the atmosphere through evaporation.Total annual rainfall amounts usually range from 1,500 mm to 2,500 mm, butlevels of

6,000 mm or more are not uncommon In general, seasons in the humid tropicsare determined by variations in rainfall, not temperature Most areas experience

no more than 4 months with less than 200 mm of precipitation per year

About 60 countries, with a total population of 2 billion, are located partly orentirely within the humid tropics (Table 1-1) About 45 percent of the world'shumid tropics are found in the Americas (essentially Latin America), 30 percent

in Africa, and 25 percent in Asia Small portions of the humid tropics can befound in other areas such as Hawaii and portions of the northeastern coast ofAustralia

The typical vegetation for the humid tropics consists of moist, wet, and rainforests in the lowlands and in the hill and montane uplands Estimates of theirextent vary The most current effort to provide reliable and globally consistentinformation on tropical forest cover, deforestation, and degradation is by theForest Resources Assessment 1990 Project of the Food and AgricultureOrganization (FAO) of the United Nations, using remote sensing imagery andnational survey data as part of its methodology (Forest Resources Assessment

1990 Project, 1992) It defines forests as ecological systems with a minimum of

10 percent crown cover of trees (minimum height 5 m) and/or bamboos, generallyassociated with wild flora, fauna, and natural soil conditions, and not subject toagricultural practices

The project estimates that forests cover 1.46 billion ha, or 48 percent of theland area (3.02 billion ha) in the tropical rain forest, moist deciduous forest, andhill and montane forest zones These forests constitute 30 percent of the land areawithin the tropical region (4.82 billion ha) and 86 percent of the total tropicalforest area (1.7 billion ha) Although they cover only 10 percent of the land area

of the world (15 billion ha), they contain one-third of the world's plant matter.Nearly two-thirds of the world's humid forests are found in Latin America, withthe remainder split between Africa and Asia

The soils of the humid tropics are highly variable Table 1-2 shows thegeographical distribution of soil orders and major suborders based on the soilclassification system developed in the United States Oxisols and Ultisols are themost abundant soils in the humid tropics, together covering almost two-thirds ofthe region Oxisols, found mostly in tropical Africa and South America, are deep,generally well-drained red or yellowish soils, with excellent granular structureand little contrast between horizon layers As a result of extreme weathering andresultant chemical processes, however, Oxisols are acidic, low in phosphorus,nitrogen, and other nutrients, and limited in their ability to store nutrients, buthave relatively high soil organic matter content Ultisols are the most abundantsoils of tropical Asia,