Chapter 10 Forestry Technologies to - Princeton

Chapter 10

Forestry Technologies to

Highlights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Agroforestry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Watershed Management. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Introduction . . . . . . . . . . . . . . . . .

Agroforestry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Agroforestry Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification and Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Technology Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Constraints and Opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Watershed Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. ... ... .Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...............Watershed Management. . . . . . . . . . . . . . . . . .. .. ... ... ... . . . . . . . . . . . . . . .

Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .General Technical Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Specific Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Constraints and Opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter IO References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...

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List of Tables

Table No. Page29.Some Prominent Agroforestry Systems in Developing Countries . . . . . . . . . . . . . 22130. Organizations That Work on Agroforestry Systems . . . . . . . . . . . . . . . ...6..... 228

List of Figures

Figure No. Page28. Effects of Poor Watershed Management~ . . . . . . . . . . . . . . . . . . . . . . 23029. Slopes and Appropriate Conservation Measures . . . . . . . . . . . . . . . . . . 23130. Cut-Off Drain to Protect Steep Forested Scarps From Landslip Hazard . . . . . . . 23231. Cross-Sectional View of Eight Types of Conservation Structures . . . . . . . . . . . . . 234

Chapter 10

Forestry Technologies toSupport Tropical Agriculture

● The medium- and long-term maintenance oftropical forest resources may depend moreon sustaining lands under cultivation thanon refining the use of the remaining forest.

Agroforestry

● Agroforestry, systems that use trees, crops,and/or animals on the same land, holds greatpromise for improving and sustaining theproductivity of lands under cultivation,

● Genetic improvement of multipurpose treespecies has great potential to increase theproductivity of agroforestry systems,

● Rigid boundaries between disciplines havedeterred agroforestry development. There isa need for a thorough rethinking of the ap-propriate institutional homes for agrofor-estry,

● Implement at ion of agroforestry systems re-lies on removing obstacles to adoption, im-proving extension services, and creating in-centives to encourage farmers to adopt agro-forestry practices.

●

●

●

Watershed Management

Damage to tropical watersheds is most eco-logically and economically significant wheresubsistence farmers and their livestock moveonto steep uplands. Improved farming sys-tems are needed that can ensure and en-hance farmers’ short-term returns and at thesame time modulate water flow.

Where flood protection for large populationsin lower reaches of river valleys depends onprotecting the vegetation on steep upper wa-tersheds, costs for conservation practices inthe uplands should be subsidized by the low-land communities.

More research on the relationship betweenland use and hydrological systems is neces-sary to give watershed managers a better un-derstanding of various management systemsand their tradeoffs.

INTRODUCTION

The major cause of deforestation and forestdegradation in most countries is land clearingfor agriculture. In many places, the quality ofland is degraded by conventional farming orgrazing practices, so the farmers and herdersmust keep clearing more and more forest. Thispractice continues because people have no al-ternatives.

Many of the technologies discussed in thisreport can help to sustain forests by makingforested land more productive and thus canhelp reduce the need for converting the landto nonsustainable uses. However, increasingthe productivity of forests alone is unlikely toprovide enough jobs or income for rapidlygrowing rural populations, For that, the pro-

219

220 ● Technologies to Sustain Tropical Forest Resources

ductivity of agriculture has to be sustained and 1.increased.

Agricultural productivity can be increasedby enlarging the area farmed, maintaining thequality of the land already in use, and increas- 2.ing the per hectare yields. Chapter 11 addressesplanning technologies to direct land clearingonto sites that are appropriate for agriculture.This chapter addresses forestry-related technol-ogies for the other two approaches. The objec-tives of these technologies are:

to enable farmers on marginal soils to con-tinue farming in one location and to main-tain or gradually increase land productivi-ty so they can stop clearing more and moreforest, andto protect and allow improvement of agri-culture in the more fertile river valleys bymodulating waterflows and reducing ero-sion and siltation from upland watersheds.

.,

AGROFORESTRY

Background

Traditional farming methods used in tropi-cal countries were developed to reduce the riskof crop failures more than to provide maximumproduction. As a result, the traditional crop-ping and grazing systems used on relatively in-fertile, dry, or erosion-prone sites often involvemultiple crops, intercropping, and complexcrop rotation schedules. However, the tradi-tional systems are not productive enough toprovide for the rapidly expanding populationsof the Tropics. They need to be modernizedand further developed.

On fertile and well-watered alluvial soilswhere traditional farming was based on mono-cropping of rice or wheat, it has been possibleto increase yields by adapting modern temper-ate-zone technologies, including applicationsof fertilizers and pesticides. But in the less wellsituated sites, many attempts to replace com-plex, traditional farming systems with modernmonocrop agriculture have failed, apparentlybecause of high risks from climate, pests, anddifficult soils and because of the complex so-cioeconomic conditions that often prevail. So,in recent years, some scientists have begun de-veloping modern technologies to improve,rather than replace, the traditional farming sys-tems (26). This approach to tropical agricuhuredevelopment is still promoted by only a smallnumber of agricultural scientists.

Agroforestry is a name for a collection ofland-use systems and technologies where

woody perennials (trees, shrubs, palms, bam-boos, etc.) are deliberately grown on the sameland with agricultural crops and/or animals ineither spatial arrangements or temporal se-quences. Agroforestry is a new word, not anew concept. The novelty lies in formally rec-ognizing that many different tree-based land-use systems possess certain common featuresthat hold great promise in the Tropics.

On fertile lands, intensive agroforestry sys-tems, like intensive agriculture, can supportdense populations. Agroforestry, however, isprobably more important for improving andsustaining the productivity of the lands withsoil fertility and soil moisture problems, andwhere lack of rural infrastructure and cashmake it necessary for people to produce mostof their own basic needs for food, fodder, fuel,and shelter.

Agroforestry Systems

Description

Agroforestry encompasses many well-knownand long-practiced land-use systems on culti-vated or grazed lands in the Tropics (table 29).Traditional shifting cultivation, bush fallowsystems, and all forms of “taungya” afforesta-tion* fall under this term, as do the home gar-dens of the wet tropics and the use of foddertrees and shrubs in the dry Tropics.

*Taungya: Burmese for hill cultivation. Agricultural crops areplanted with trees used for wood production.

Table 29.—Some Prominent Agroforestry Systems in Developing Countries

Mediterranean and Eastern, Central, and Arid and semiaridWest Africa American TropicsMiddle East

1. Olive + cereals(on terraces, ‘ban-quettes’, ‘cuvettes’,etc.)

2. Poplars along irriga-tion canals

3. Trees for sand dunereclamation

Humid West AfricaSoutheast Asia

1. Agro-silvicultureSouthern Asia

Trees in perennialcash crops (coffee,cacao, tea)Trees for organicmatter and mulchwith annual cropsTree live fencesWindbreaks and shel-terbeltsTrees as support forclimbing commercialcropsTaungyaShifting cultivationsystems

1. Taungya2. Plantation crops +

arable crops3. Commercial trees and

fruit trees with crops4. Live fences + shel-

terbelts

1.2.

3.

4.5.6.7.

1.

2.

1.

TaungyaCacao/food crops/forest complexPlantation crops (oilpalm/rubber) and rootcrop complexCoffee + bananaMixed perennial cropsGum arabic + milletShifting cultivation/bush fallow systems

1.

2.

1.

2.

3.

1.

Use of trees on farm-lands for protectiverole (windbreaks,dune fixation)Productive + protec-tive role of trees onfarms (A. albida/Leu-caena + agriculturecrop systems)

1.

2.

3.4.

5.

6.7.

1.2.

1.

2.

3.4.5.6.

7.

Commercial treesamong cropsFruit/shade treesamong cropsLive fencesShelterbeltsTaungyaShifting cultivationsystemsIntercropping in plan-

5. Various trees on farm-lands for productivefunctionsVarious forms ofshifting cultivationMedicinal plants +agriculture species

4. ‘Huertas’ - small plotsirrigated crops +fruit trees

5. Aromatic, medicinalarid fruit trees withcrops

tation crops (rubber,oil palm, coconut)

6.

7.

2. Silvo-pastoral1. Pasture in forest

plantation2. Pasture in secondary

forests3. Commercial trees in

pastures4. Fruit/shade trees in

pasture5. Fodder trees6. Coconuts + pasture

3. Agro-silvo-pastoral

Pasture under treesPlantation crops +cattle grazingFodder trees andshrubsFruit trees and com-mercial trees inpastures

1. Oak forest + grazing2. Pig breeding and

forestry3. Range land

improvement

Gum arabic +livestockPlantation crops(coconut/cashewpasture

Nomadic/semi-nomadic/transhumanSedentary livestockgrazing systems/browsing systemsFodder tree/shrubsystems

Trees in pasturePasture in natural

1.2.

3.

4.

1.

2.

regeneration forest3. Trees lopped for

fodder4. Trees used for

+

browsing

Agriculture plantationcrops (coconut, rubber,fruit, trees) withcrops and pastures

Plantation crops +arable crops +livestockAgriculture tree crops+ grazing in forest

Range land manage-ment

Coconuts/other plan- Forestry dominating1.

2.

3.

4.

Crops and grazing inplantationsAgriculture tree crops+ grazing in forestplantationMultipurpose treeswith crops/animalsIntegrated farmingsystems with agricul-ture plantation crops(rubber, coconut, oilpalm)

1.tation crops + foodcrops + grazing

2. Coffee + banana +dairying

3. Horticultural complexsystems

4. Plough culture com-plex systems

(forest lands)2. Agriculture dominating

(crop lands)3. Livestock dominating

(crop lands)

Table 29.—Some Prominent Agroforestry Systems in Developing Countries—Continued

Mediterranean and Eastern, Central, andSoutheast Asia Southern Asia

Arid and semiaridMiddle East Humid West Africa West Africa

4. Home gardensVarious forms of 1. Multistory plantmultispecies canopies in humidcombination

2.

5. Others1. Silviculture in 1.

mangrove forests2. Agri-silvi-fishery 2.3. Trees on bunds in 3.

fish breeding ponds4. Swidden farming 4.5. Fuelwood agroforestry

regionsArid/semiarid systems

Mixed perennial 1.croppingIrrigation systemsVarious site-specificsystems 2.Fuelwood systems

3.4.

Mainly in large cities Various forms

New system inMorocco (spice

1. Pastoral systemsplan- with corral farming

tation for erosion (highland/lowland)_control) 2. Mixed perennialAgriculture + croppingforestryFruit trees in desertsMushroom cultivationin forest

SOURCE: Anonymous, “A Global Inventory of Agroforestry Systems,” Biomass :241-245, 1983

Various forms

1. Oasis2. Irrigation systems3. Various site-specific

systems

American Tropics

Various forms

Mixed perennialcropping

Ch. 10—Forestry Technologies to Support Tropical Agriculture ● 223—

Rubber trees interplanted with a cover crop of Pueraria phaseoloides and grazed by cattle is one typeof agroforestry system

Agroforestry systems attempt to optimize ●

ecological and economical interactions be-tween various components (trees and shrubs/ ●

crops and animals) to obtain a higher, morediversified, and/or more sustainable total pro-duction than is possible with any single landuse. Typical characteristics of such systems ●

are: 1) two or more species of plants (or plantsand animals), at least one of which is a woody ●

perennial; 2) two or more outputs; and 3) a pro-duction cycle of more than 1 year.

Agroforestry can provide many goods and ●

services. Depending on the particular situation,it may:

increase and improve food productionyields;produce firewood and a variety of otherraw materials from shrubs and trees forfarmers’ subsistence, for local sale, andsometimes for export;protect and improve the soil’s productivepotential;improve social and economic conditionsin rural areas by creating jobs and incomeand reducing risks; anddevelop land-use systems that draw onboth modern technologies and traditionallocal experience and that are compatible


plantation trees has attracted much attentionas a promising way of increasing total yieldfrom the land. An example is the Jari Projectin Brazil, where seeding the pine plantation(Pinus caribea) with forage grass (Panicummaximum) reduced the need for weed control.The cattle then increased the total income fromthe system (21).

Many commercial timber and pulpwoodplantations in the Tropics have been estab-lished through the “taungya” system. Farmersor forest laborers are allowed to grow crops fora few years during land preparation and earlyplantation phases. In exchange, they weed andcare for the young trees. After an agreed-uponperiod, the farmers move on. Taungya has beenused for more than a century and has been ap-plied throughout the Tropics. Although well-planned taungya can provide a sequence ofnew ground for shifting cultivators, it removesthe land from agriculture for a period dictatedby the biology and economics of the forest cropand not by the needs of farmers or forestlaborers.

The widespread use of this system and itsmany local variations is a clear indication ofits success (25). The practice has been success-ful with Terminalia, Triplochiton, and severalMeliaceae in West Africa; Cordia in Surinam;Tectona in Trinidad; and Swietenia in PuertoRico (45). In Nigeria, the system has been ap-plied in both wet and dry zones for tree andfood production. In that country, it has beencredited with providing enough food for about700,000 people, or about 1 percent of Nigeria’sfood needs (13).

The increased use of commercial, commod-ity-oriented agroforestry is attractive in theory.However, the areas under perennial agricul-tural tree/shrub crops occupy about 8 percentof total arable area in developing countries to-day (27). Of this, only a minor part is used forintercropping or grazing. Another 2 millionhectares of perennial agricultural tree planta-tions could be established by the year 2 0 0 0without encountering serious marketing prob-lems (38). But this approach has limited poten-tial for substantially alleviating land problems.Since commercial agroforestry will be intro-

Ch. 10—Forestry Technologies to Support Tropical Agriculture ● 225

duced only where opportunities for profits areclearly perceived, it is unlikely to be used oninfertile land or by people who are not entre-preneurs. This objection applies less to timberplantation land, where small improvements intaungya could produce significant increases infood production. Forest plantation lands couldthen support considerably more people thanthey do now.

Intermediate agroforestry systems are wherefarmers with small to medium sized landhold-ings combine production of perennial crops forcash with annual crops for subsistence. Someof these systems are oriented toward commer-cial production, but they are small and the landis operated by individual farmers. Others aresimilar to subsistence systems. An example isthe combination of gum arabic trees (Acaciasenegal), which can provide good cash incometo farmers, with millet in the Sudan. Anotherintermediate level agroforestry system occurswhen commercial firms enter into contractswith small- and medium-scale farmers to pro-duce raw materials. The British-AmericanTobacco Co. in Kenya has contracts withfarmers who grow tobacco and the fuelwoodneeded for curing it, together with their ownfood crops.

Coffee forms the economic basis for manyintegrated land-use systems in this category,particularly on fertile soils in tropical uplands.In the East African highlands, multistory pro-duction is common. Timber trees such as Al-bizzia and Grevillea shade coffee interplantedwith bananas and beans (33). Similarly, in Cos-ta Rica coffee is grown under the shade of bothtimber trees (Cordia alliodora) and multi-purpose trees (Erythrina spp.) (7,8). Anotherimportant crop in tropical small-holder agro-forestry is coconut. Planting food crops andgrazing cattle under coconuts are commonpractices in the wetter parts of Sri Lanka, India,Southeast Asia, and the Pacific regions (28).

Most of the economically and ecologicallysuccessful examples under this category arefound in areas having relatively fertile soils,good communications, and existing market in-frastructure. But many obstacles can be en-

countered when expanding permanent cashcrops into less favorable areas, where infra-structure and markets are underdeveloped,where land tenure is uncertain, or where theenvironment imposes serious restrictions onintensive land use. Still, there is promise forimproving existing systems through the intro-duction of improved varieties of tree crops,fruit trees, and compatible food crops, as wellas application of fertilizers.

Subsistence agroforestry systems areoriented toward satisfying the basic needs offarmers for food, fuel, and shelter, with someproducts sold for cash income. Such systemsare practiced by a large portion of the popula-tion of the tropical world, from livestock herd-ers in semiarid areas to shifting cultivators inrain forests. These systems usually are prac-ticed where serious ecological and/or socioeco-nomical constraints exist. Infertile soils, ero-sion, and/or drought can be major physical lim-itations. Insecure land tenure and lack of in-frastructure, capital, extension services, andeducation are common socioeconomic con-straints.

Many different subsistence agroforestry sys-tems exist. Shifting cultivation and bush falloware practiced in many forms throughout thetropical world. One well-known form of per-manent traditional agroforestry is the homegardens of Southeast Asia, characterized by amultistory mixture of many species of trees,shrubs, climbers, palms, tubers, and often an-imals (pigs and poultry) (16). Other agroforestryin Asia integrates rice production with treesfor windbreaks, boundary demarcation, andfuelwood production (6,16).

Oases are a prototype of agroforestry in aridlands. They contain ponds to water livestockas well as an upper story of multifunctionaltrees and a lower story of agricultural or hor-ticultural plants. Though only comprising asmall area endowed with water and fertilesoils, they can be extremely well-balanced hu-man ecosystems with species mixture, multi-story structure, and near-perfect recyclingprocesses (44).


.

Photo credit: K. Parker

Chinarnpas in Mexico are centuries-old food production systems used where water is available year round. Narrowirrigation/drainage canals surround the plot and control water supply; mud dredged from canals serves as organicfertilizer; aquatic vegetation serves as “green manure;” fish that colonize the canals provide additional protein; trees

planted along the canals hold the soil in place as well as providing other products

Millions of people practice agroforestry inareas with serious physical and socioeconomicconstraints. The problem of improving the pro-ductivity and sustainability of these people’sagriculture and agroforestry methods is of anentirely different magnitude than that of im-proving commercial and intermediate agrofor-estry systems. Reaching farmers can be diffi-cult, and where subsistence farmers can bereached, they need to be convinced that thecosts, risks, and benefits of new technologiesare favorable. The time between planting a treeand achieving significant yields may involverisks that subsistence farmers cannot take. Italso can be difficult to convince land users tomake long-term investments when land tenureis uncertain. Subsistence agroforestry holds

great potential for improving land use but hasurgent need for technology improvement.

Technology Issues

In general, the concept of agroforestry as asustainable approach to land use is sound. Theaim is to create productive farming systemsable to supply an increasing and sustainableoutput of basic needs, including cash. Main-taining soil ferti l i ty, preventing erosion,moderating microclimate, and other environ-ment-enhancing roles of the tree/shrub compo-nent apparently do help sustain production.

A growing body of information exists on thevarious agroforestry technologies, but this ismainly descriptive and qualitative. Most scien-

Ch. 10—Forestry Technologies to Support Tropical Agriculture . 227

tists’ interest has been in the tree/shrub com-ponent (e. g., potential tree species, their use,and management) because of the novelty ofusing trees and shrubs in agricultural andpastoral lands,

During the last 5 years, many agroforestryresearch projects have been initiated at univer-sity forestry departments and forestry researchinstitutes. These generally study the long-termeconomic and ecological productivity of vari-ous trees, planted at different spacings, andcombined with a food crop, which is often usedas a “test” crop to quantify the competitive orsoil-improving influences of the tree.

Only certain trees and crops prove to be com-patible, Rubber trees, for instance, produce somuch shade that underlying pasture often be-comes useless within 3 years. Oil palm soils areoften clayey and wet and animals tend to com-pact the soil and damage tree roots (17). Somecrops such as sorghum, millet, and pigeon peaare highly competitive with other plants and,thus, may not be suitable for intercropping.Other crops —maize, cotton, and dry rice—areless competitive and can be intercropped. Eachsystem has complex problems of intraspecificand interspecific competition. The aim of ex-perimental research is to optimize combina-tions of agriculture, pastoralism, and forestryover space and time.

Tropical research and development organiza-tions have become much more interested inmultipurpose trees. The legume family has at-tracted particular attention. In general, leg-umes, through their bacterial relationship, canimprove soil fertility and produce good-qualityfuelwood as well as leaves and pods withfodder and food value. Different legume spe-cies also are adapted to a wide range of ecolog-ical conditions. Many multipurpose species arefound in the legume genera Acacia and Pro-sopis. Several nonlegume multipurpose speciesare equally interesting because of their generalversatility, adaptability to less favorable sites,and yield of valuable products. An example isthe neem tree (Azadirachta indica) w h i c horiginated in the dry zones of Asia. It is an ex-cellent timber, fuelwood, and shade tree and

produces tannins, insecticidal chemicals, andfuel/lubricant oil (35).

The greatest potential for improving agrofor-estry systems lies in the practically unexploredfield of genetic improvement of multipurposetrees and shrubs (26). Selecting the species andvarieties that are best adapted to particular pur-poses and site conditions for which the agro-forestry systems are intended is the first step.Traditional agroforestry systems have beendoing this gradually for centuries, but now withmodern communications and techniques forreproducing, transporting, and testing varie-ties, it is possible to greatly accelerate theprocess.

Because the scientific attention to multipur-pose trees is so new, examples of the gains thatcan be achieved by this selection and matchingprocess are rare. The interest in single-purposeuse of trees is older, and gains with these il-lustrate the potential for multipurpose trees.For example, results from 32 sites in 18 coun-tries show that productivity gains of severalhundred percent could be achieved in eucalyp-tus trees simply by selecting the best-adaptedprovenances for prevailing conditions (31).

The second step, which can begin before thefirst is completed, is tree breeding—crossingplants to combine particular desired character-istics, such as fodder and fuel production quan-tity and quality, rooting characteristics, phenol-ogy favorable for interplanting with annualcrops, nitrogen-fixation, pest resistance,drought resistance, or the ability to withstandother stresses.

The potential for agroforestry systems im-provements to be adopted on a large scale byfarmers and pastoralists is difficult to assess.If the relevant land-use problems have beenidentified and an ecologically, economically,and socially well-adapted agroforestry solutionis demonstrated to be feasible, then agrofor-estry improvements may be adopted, However,finding locally acceptable solutions to prob-lems that are perceived by farmers is crucial.Sophisticated trials on the best spacing of treesover crops are, for example, not particularly


relevant if farmers are not interested in thatparticular tree species.

The constraints and problems encounteredin developing and disseminating agroforestrysystems are many. Millions of farmers andlandless people are spread over vast expansesof tropical lands. Rapid population growth, in-secure land tenure, erosion, droughts, floods,declining soil fertility, lack of infrastructure,political instability, illiteracy, and other devel-opment problems often characterize thosebroad regions where agroforestry approacheshave a potential role to play. Therefore, agro-forestry development cannot occur in isolationfrom general social and physical constraintson rural development.

Constraints and Opportunities

Agroforestry techniques can be used toaddress particular land productivity problems.However, most information on the techniqueis qualitative and advocative. Present researchand field implementation efforts are more adhoc than systematic.

Critical analyses of agroforestry’s constraintsand opportunities must be made if it is to bene-fit from application of the scientific method.Systematic quantitative information can pro-vide a basis from which researchers can formu-late hypotheses and design efficient researchstrategies to develop new agroforestry systems,refine old ones, and adapt proven ones to otherareas. This is necessary to ensure that onlytechnologies with high probability of successare brought to large-scale field implementation.

The effort to organize and assess existing na-tional and international experience in tradi-tional agroforestry technologies and to iden-tify promising technologies for further develop-ment is under way at the International Coun-cil for Research in Agroforestry (ICRAF). Tech-nologies that need refinement and farm valida-tion include alley cropping, improved fallows,live fences, contour hedges, mulch productionwith tree species, and fodder production. Somesuch programs already exist, but efforts shouldbe made to strengthen these (table 30).

Table 30.—Organizations That Work onAgroforestry Systems

1. International Council for Research in Agroforestry2. Centro Agronomical Tropical de Investigation y

Ensenanza (CATIE)3. International Tree Crop Institutes (U. K., U. S. A., and

Australia)4. Nitrogen-Fixing Tree Association5. National Academy of Sciences (fuelwood and legume

tree species)6. Commonwealth Forestry Institute (information,

research, and training)7. East-West Center (dissemination and exchange of

agroforestry information)8. United Nations University (workshops and research

programs at cooperating institutions)9. Some components of UN ESCO/MAB research

program10. Some developed country universities11. Some CGIAR institutions (e.g., IITA in Nigeria on alley

cropping and CIAT in Colombia on Leucaena andErytherina)

12. FAO’S Panel of Experts on Forest Gene Resources(data collection and assessment)

SOURCE: B. Lundgren, “The Use of Agroforestry to Improve the Productivity toConverted Tropical Land,” OTA commissioned paper, 1982,

Since agroforestry cuts across several disci-plines, it requires an integrated and multidis-ciplinary approach. Agronomists, foresters,ecologists, sociologists, anthropologists, andexperts in other related disciplines have ac-cumulated much data on various tropicalmixed-cropping systems. Such information canbecome the foundation for research programsto explore ways to integrate sustainable pro-duction of food, forage, and fiber needs on ap-propriate lands. However, too little communi-cation or coordination occur among these dis-ciplines to formulate a strategy for develop-ment of agroforestry technologies. This con-straint would be alleviated if interdisciplinaryteams were established to conduct research onintegrated land-use systems (26).

Agroforestry needs an institutional home toensure its implementation. It is considered asubdivision of forestry, but forestry institutionsdeal with forest land. They seldom address theproblems facing individual users of small andmedium size holdings of cultivated lands. For-estry institutions, in general, do not have therange of expertise needed to develop agrofor-estry’s full potential. The major potential foragroforestry lies in the integration of trees into

Ch. 10—Forestry Technologies to Support Tropical Agriculture “ 229

agricultural and pastoral lands. The develop-ment of these lands is the mandate of agricul-tural institutions, which are not explicitly man-dated to deal with agroforestry.

Rigid boundaries between disciplines affectfunding of agroforestry research, development,and implementation. Forestry and agricultureoften compete for both funds and land. In in-ternational agencies, agricultural divisions arebetter institutionalized, more prestigious, and,thus, better funded than forestry divisions. Theforestry funds that do exist usually are chan-neled to conventional forestry activities.

The ratios of international financial supportfor research in tropical agriculture, forestry,and agroforestry, respectively, are about200:1O:I (26), This may underestimate the rela-tive magnitude of agricultural research sup-port. Although the importance of research isclearly recognized in agriculture, the attitudeof development assistance donors toward re-search in forestry is cool. Thus, as long as agro-forestry funding is channeled through forestrydepartments, little hope exists that sufficientresearch funds will be available. A thoroughrethinking and revision of the appropriate in-stitutional home for agroforestry is needed.

The large-scale promotion of agroforestrywould require incentives to encourage farmersto adopt practices that involve initial risks anddelayed returns. Integrating trees into agricul-tural or pastoral systems is unlikely to succeedwhere short-term, insecure leases for use ofland are prevalent, where trees automatically

become the property of the government, orwhere nonrestricted communal grazing or treecutting rights exist. Neither are farmers likelyto achieve large-scale cash crop production ofwood (i.e., fuelwood, poles, pulpwood, etc.]where prices are set so low that growing treesis not profitable.

To alleviate these constraints, tropical gov-ernments will need to identify and remove con-straints in land tenure and provide incentivesand extension services. Incentives may take theform of credits and loans that reduce initialcapital outlay and minimize risk of failure. Ex-tension services can facilitate supply of mater-ials, train farmers, and make followup visitsto monitor progress of agroforestry develop-ment. Unfortunately, forestry and agroforestryextension efforts often suffer from: 1) lack ofstaff with adequate training, 2) lack of networksof on-farm demonstration plots, 3) inconsistentefforts, 4) difficulty obtaining good seeds ofmultipurpose tree species for mass distributionto farmers, and 5) lack of infrastructure.

As institutional interest and support for agro-forestry increase, it is necessary to take stepsto ensure that the enthusiasm does not lead todisappointment and a sharp reduction of sup-port. Development assistance agencies andresearch institutions have not begun, collec-tively or individually, to formulate a strategyto assure that the necessary and sufficient stepsare taken to develop the potential of agrofor-estry,

WATERSHED MANAGEMENT

Background

In an undisturbed watershed, the dispositionof rain and snow melt is determined by a com-plex interaction of terrain, soil, climate, geol-ogy, and vegetation. Unfortunately, somecommon land uses seriously disturb thevregetative cover so that both the amount ofwater that upper catchments can hold tempor-arilv during prolonged or heavy rains and the

proportion of rain that percolates into the soilare seriously reduced. This results in muchgreater variations in the seasonal river flows,greater sediment loads during peak flows, andoften a greater proportion of the total rainfallrunning off before it can be used by trees orcrops (fig. 28),

For example, denudation of water catchmentareas in the Indus River svstem has led to

230 . Technologies to Sustain Tropical Forest Resources— .

Figure 28.-Effects of Poor Watershed Management

1.

Overgrazing, deforestation, misplaced cultivation, or carelessly bulit roads In

floods far higher in the last 25 years than dur-ing the previous 60 years and has increased ser-ious silting in the reservoirs and canals ofPakistan’s irrigation system (32). In recentyears in India, the cost of repairing flood dam-age below the Himalayan catchments has been,

on average, US $250 million a year, in addi-tion to losses of production and livelihood suf-fered by millions (39).

Technologies can probably be developed andimplemented to help reduce these economicand human costs. The solution to these prob-lems of land misuse depends foremost on de-veloping improved methods of land use that areboth more profitable to local communities andalso give appreciably better control of the waterflow. Soil conservation structures (e.g., terrac-ing), revegetation, and appropriate farming sys-tems are technically adequate to contain thecurrent land degradation trend, but many ofthese techniques are too expensive for thefarmers living in the upland areas.

Watershed Management

Description

Watershed management is concerned withcontrolling water flow above and below theEarth’s surface from the upper to lower regionsof drainage basins. Management of the upperwatersheds aims to maintain or to improve thetiming, quantity, and quality of water that isused in more intensively developed lowlands.

The natural vegetation on tropical mountainslopes that receive high rainfall is closedcanopy evergreen forests, sometimes inter-rupted by shallow-soiled grass or swamp areas.Evergreen forests provide temporary storagefor heavy rainfall, thus delaying water’s move-ment into streams and reducing peak stormflow. The temporary storage occurs partly onthe wetted canopy, partly in the deep forestground-litter, and partly in the topsoil madeporous by vegetation and soil fauna. Some wa-ter drains through these porous surface layersto streams. Some water infiltrates to rechargeground water and thus maintain dry-seasonspring flows. Some water is evaporated fromthe wet canopy and some is transpired backinto the atmosphere through the foliage.

Watershed management includes soil conser-vation, road planning, contour cultivation,grassed waterways, cutoff drains, grass plant-ing on steep banks, and other techniques to

Ch. 10—Forestry Technologies to Support Tropical Agriculture ● 231

control water’s impact. Soil stability, agricul-tural productivity, and the quality of water sup-plied to the lower reaches of the watershed canthus be maintained. Watershed managementis an economic necessity where there is invest-ment downstream in reservoirs for hydropow-er and irrigation or densely settled areas inzones of flood hazard.

General Technical Principles

The choice of technologies for watershedmanagement and rehabilitation varies with top-ography, accessibility, and population densi-ty. One of the best ways to protect downstreampopulations from excessive siltation and flood-ing is to maintain forests on all slopes steeperthan 100 percent grade (45 O). Where steepslopes have been cleared, they should be closedto livestock, protected from fire, and then sta-bilized by planting trees for fuel and fodder,In some cases, simple protection will sufficeto permit natural regrowth. For slopes between100 percent and 20 percent, land should notbe cultivated except where the soil is stable anddeep. Here, cultivation can be done safely only

where level or preferably backsloping terracesare maintained. For slopes less than a 20 per-cent grade, a variety of agricultural technol-ogies for minimizing soil loss can be used(fig. 29),

In sparsely populated watersheds, wherethere are few or no people living in the upperregions of river basins, tropical watershedmanagement is a matter of maintaining or re-storing the vegetative cover that controls waterflows. If forests are intact and populations arelow, intensive management is not necessary,The best and least expensive method of pro-tecting these forests is to designate them parksor protected areas. However, effective parkmanagement can be difficult to obtain. Itshould be based on a comprehensive plan thattakes into account the previous, current, andfuture resource needs of people who livearound and below the protected forest.

The greatest watershed problems in the Trop-ics, however, are not in the upper sparsely pop-ulated reaches of river basins. They are in pop-ulated watersheds, where the upper regions

Figure 29.—Siopes and Appropriate Conservation Measures

Stone-walledlevel benchterrace “

●

.●

narrow-basedterraces orhillsideditches

SOURCE: H. C. Pereira, “Soil and Water Management Technologies for Tropical Forests,” OTA commissioned paper, 1982,


are farmed and grazed, and where mainte-nance of natural closed forest cannot beaccomplished without displacing substantialnumbers of people.

In some cases watershed management tech-nologies can be used without displacing peo-ple from upland areas. For example, where for-ests cover steep escarpments below settle-ments, runoff from the upper slopes can over-load the forest soils and cause large-scale land-slips, especially on geological dip-slopes (fig,30). Such landslips are common in Nepal, partsof Zaire, and in other places where sedimen-tary rock formations are tilted. It maybe possi-ble to stabilize these areas through reforesta-tion and cutoff drains, which intercept andconvey runoff to stable drainage lines and,thus, protect the soils from saturation. Thesedrains need to be protected as well, possiblywith tree cover.

The most critical need for watershed man-agement occurs in the forests immediatelyabove the limits of cultivation (32). Often, these

Figure 30.-Cut”Off Drain to Protect Steep ForestedScarps From Landslip Hazard

Cut-off drain

SOURCE: H C. Pereira, “Soil and Water Management Technologies for TropicalForests, ” OTA commissioned paper, 1982.

are under great pressure from populationgrowth. Such forest areas are usually too steep,shallow-soiled, and rock-encumbered for con-tinuous cropping. Yet, agricultural communi-ties have in many countries established tradi-tional rights for grazing or for collection of fueland fodder from these lands. Massive overgraz-ing inflicts most damage, often preventing theemergence of any effective ground cover.These activities promote erosion, which con-sequently forms major gulleys (29). Some areasare so steep and unstable that the only optionis to prohibit all active use. In moist forestareas, if soil nutrients have not been eroded orleached away, the ability of the land to recu-perate can be high. However, sustainable alter-natives must be found for the displaced peo-ple, or they will, sooner or later, begin to over-use the slopes again.

Tropical forests on land with easy access andgentle topography are likely to be cleared foragriculture or other land uses. When such areasare logged and cleared, soil and water manage-ment problems do occur. Governments shouldrestrict the use of more damaging heavy equip-ment to well prepared roadways. Cable ways,winching, and use of lighter logging and landpreparation machinery, though likely to bemore costly, can be less damaging to the soil.Operational trials with equipment designed toreduce soil damage should be conducted to testand demonstrate its utility (32).

Specific Technologies

The primary technologies available to dealwith watershed problems are those associatedwith alteration of the surface geometry, reveg-etation, and improved farming.

Soil Conservation STRUCTURES

A common method to reduce soil erosionfrom hills in the humid tropics is to change theslope steepness and length. For example, asteep slope can be changed to many continuousflat strips running along the contour across ahillside (terraces), or a long slope can bechanged to a series of shorter slopes by using

Ch. 10—Forestry Technologies to Support Tropical Agriculture Ž 233

discontinuous types of structure. The objectiveof both measures is to divert runoff along thecontour toward protected drainage channelsor waterways at a velocity that reduces erosion,

These and other technologies not only havephysical requirements but financial, labor, andland-use rights requirements. The cost of vari-ous conservation structures per unit area de-pends on slope, soil, type of terraces, width ofbench, presence of rocks or tree stumps, andthe tools needed to build them, Since the struc-tures can be expensive, a cost-sharing or sub-sidy scheme may need to be introduced by thegovernment. Farmers often are reluctant to in-vest the time and effort to build such structuresbecause of insecure land tenure. Further, laboroften is not available,

Few critical, full-scale studies of terracinghave been reported from the Tropics. Many

small runoff plot measurements are made, butthese do not reproduce the conditions of culti-vation by oxen or tractor that determine in-filtration, runoff, and erosion on a practicalscale.

REVEGETATION

Steep mountain areas that have been clearedshould be reforested to protect water and soilresources. If the objective is to stabilize soil andstreamflow, the least expensive method is toprotect the area from grazing livestock and fireso it can regenerate naturally. In some caseswhere erosion has been severe, natural regen-eration needs to be augmented by seeding withgrasses, legumes, and shrubs. More expensivereforestation investments are appropriatewhere the objectives include production offuel, fodder, and timber of desirable species;where grasses and shrubs will not provide

Terracing

Terraces not only control erosion but also can be used to facilitate irrigation and drainage,as well as cultivation. Reversed-slope benches, continuous or discontinuous, differ in width to suitdifferent crops and slopes. Benches improve drainage by concentrating runoff at the outside ofthe bench and then drain it along a controlled lateral gradient to a protected waterway. They aresuited to annual, semipermanent, and mixed crops and can be applied on slopes up to 300. Varia-tions of conservation structures include (fig. 31):

● Bench terraces: a series of level strips running across the slope supported by steep risers.These can be used on slopes up to 25° and are mainly used for upland crops.

• Hillside ditches: a discontinuous type of narrow, reverse-slope bench built across the hillslope in order to break long slopes into many shorter ones. The width of the cultivable stripsbetween two ditches is determined by the slope of the land. They are inexpensive, flexible,and can be built over a period of years. This treatment can be applied to slopes up to 250.

● Individual basins: small, round benches for planting individual plants. They are particular-ly useful for establishing semipermanent or permanent tree plots to control erosion. Theyshould normally be supplemented by hillside ditching, orchard terracing, and crop covering.

● Orchard terraces: a discontinuous type of narrow terrace applicable on steep slopes up to300. Spacing is determined by distance between trees. Spaces between terraces should bekept under permanent grass or legume cover.

● Intermittent terraces: bench terraces built over a period of several years.● Convertible terraces: bench terraces with the spaces between terraces planted with tree crops.● Natural terraces: constructed initially with contour embankments (bunds) 50 cm high on

slopes not over 70 and on soils having high infiltration rates.Ž Hexagons: special arrangement of a farm road that surrounds or envelops a piece of sloping

land treated with discontinuous terraces which are accessible to four-wheeled tractors. Thistreatment is primarily for mechanization of orchards on larger blocks of land and on slopesof up to 20°.

234 • Technologies to Sustain Tropical Forest Resources

Figure 31 .-Cross-Sectional View of Eight Types of Conservation Structures

(All reverse-sloped benches)

l -bench ter races6-conver t ib le ter races

I 5- in termi t ten t te r races

7-natural terraces

8-hexagonS

Unit hexagon

SOURCE: T c, Sheng, “The Need for soil Conservation Structures for Steep Cultivated Slopes in the Humid Tropices, ”E. W. Russell (eds.) (New York: John Wiley & Sons, 1981), pp. 357-372.

Tropical Agricultural Hydrology, R. Lai and

Ch. 10—Forestry Technologies to Support Tropical Agriculture • 235

enough runoff control; or where protectionfrom fires cannot be sustained indefinitely.

Efforts to establish tree cover on long steepslopes must overcome the erosion and land-sliding that may be common to those sites. Forinstance, primitive dams made of rock, soil,and, if available, tree stems and branches canbe built in gullies to slow water and trap soiluntil trees can be established. Channels andwalls can be built to divert water flow fromvulnerable areas. Water-spreading techniquescan be used to distribute runoff water overrelatively flat areas, reducing its erosive poten-tial, Terracing, contour hedges and furrows,and low retaining walls can control sheet ero-sion. To establish trees it may be necessary touse contour planting, with graded hillsidebunds or narrow-based terraces at suitable in-tervals to lead runoff into prepared drainagelines.

Perennial tree crops such as tea, oil palm,rubber, or coconut can be almost as effectiveas natural forest to regulate water flow, pro-vided that soil conservation measures such asterraces and sound engineering of roads areincluded. Stormflow control, however, may notbe fully restored, In Kericho, Kenya, wheremeasurements of runoff from a tea plantationwere taken, stormflow peak, although small,remained twice that from a comparable undis-turbed forest. Thus, if large areas of forest areto be converted to tea or other estate crops, ad-ditional reservoir storage will be needed tomodulate peak flows (32),

The same is true for fast growing forest plan-tations with short harvesting schedules. Careis needed during harvesting to minimize neg-ative impacts. Selection of tree species also isimportant. Eucalyptus, for instance, plantedclose together will eliminate all vegetativeground cover and this can accelerate soil ero-sion (40). Pure stands of trees that may havetheir leaves closed during rainstorms, such asLeucaena, provide only partial soil protection(5), Therefore, it maybe necessary to includea second story of shrubs to minimize the im-pact of rain drops falling through or from thecanopy.

In areas with a dry or seasonally dry climate,flood control and ground water recharge maynot be considered so important as maximizingthe amount of water delivered to reservoirs orto farms and cities in the lower regions of thewatershed. In this case, watershed managersmay decide that the closed forest consumes toomuch water and may prefer to maintain a grasscover, since evapotranspiration loss is greaterfrom tall trees than from low shrubs or grass.On the other hand, in some dry, mountainousareas, trees that collect moisture on their leavesfrom wet air are the best mechanism to re-charge ground water (9). Overall, the negativeand positive impacts of grass and tree coverunder tropical conditions are poorly known.Grass cover may increase the amount of runoffand flow rates may not be modulated, thusmaking dams necessary. Improvements in thescience of hydrology are needed to provide bet-ter data to calculate the tradeoffs of manage-ment options,

Complete grass cover is an acceptable vegeta-tion for tropical watersheds only where dryseason grazing and burning can be rigorouslycontrolled. Thus, watershed management be-comes livestock and fire management as well.A strategy to reduce livestock damage in water-sheds should include improving draft powerand milk production per head so as to encour-age farmers to keep fewer and better qualityanimals. This can be accomplished by intro-ducing superior animals, by providing effec-tive marketing systems, and by establishinglivestock exchange programs. The danger ex-ists that farmers will be encouraged to keepmore livestock in addition to or in place offarming.

Fire is used to eliminate old grass growth andimprove the quality of grasses for grazing.However, repeated burnings can damage soilby destroying soil organic matter and conse-quently reducing soil microbiological popula-tions. Human-induced fire is common in grass-lands and is difficult to control. If grass is go-ing to be the primary vegetative cover or eventhe cover while trees are small, methods mustbe devised to control fire as well as regulateits use.

236 . Technologies to Sustain Tropical Forest Resources

Encouraging stall or pen feeding also reduceslivestock damage. On steep slopes in Pakistan,farmers participating in a reforestation pro-gram cut naturally regenerated grass underyoung trees and carry it to their stall-fedlivestock. More fodder is produced this waythan when the animals graze the hillsides.Another way to encourage stall-feeding is toprovide incentives—e.g., employment of resi-dents to plant fuel and fodder trees and tall fod-der grasses on denuded common land and ineroding gullies. Stall feeding also facilitates thecollection of manure for use as fertilizer.

However, stall feeding can be difficult to im-plement. Local constraints can develop suchas increased need for labor to carry water, toharvest and transport fodder, and to clean upand spread fertilizer. Therefore, informationon who does these jobs (often women) andwhether they have time to take on these newtasks should be gathered before implementingsuch a program.

Fodder supplies can be increased by plantingfodder trees or by introducing annual fodderspecies as a second rotation crop in permanentcropping areas. Fodder trees, pasture grasses,and legumes can be planted on embankmentsof terraces, on risers of terraced farmlands,near houses, and on other marginal land spots.Once vegetation is reestablished on the de-nuded site, controlled grazing may be allowa-ble. However, soil compaction by livestocksometimes inhibits later natural regenerationand increases surface runoff, thus causing ero-sion again.

Livestock management problems in water-sheds become more difficult in drier climates.Semiarid lands present the most urgent chal-lenge. They characteristically have higher rain-fall variability and greater stresses from tem-perature and dessication, so the land and veg-etation are more prone to rapid deteriorationunder misuse. Creative measures must be for-mulated to make it profitable for livestockraisers to limit the number of livestock and tocontrol the timing of grazing.

FARMING SYSTEMS

Damage to watersheds is most ecologicallyand economically significant where subsis-tence farmers and their livestock move ontosteep uplands because they lack other alter-natives. Mechanical structures and replantingprograms will not be implemented adequate-ly unless farmers and herders have incentivesto invest their labor in conservation practices.

Where much of the population in a catch-ment area is dependent on agriculture, themost effective component of a watershed man-agement strategy may be to increase produc-tion per unit area of land on the best sites.Other components include: agroforestry andother cropping systems that eliminate tillageor reduce it, contour plowing, timely sowingof seeds on contours, increasing crop plantdensity, and using improved seeds, fertilizers,and pesticides (48). On steep slopes farmers canbe encouraged to plant hedges of nitrogen fix-ing trees or bushes on the contour, adoptmulching techniques, and interplant with leg-umes and pulses to reduce sheet erosion. Insome places, fodder tree farming or bambooplantations may be appropriate (39).

Some constraints to adoption of these prac-tices are the farmers’ skepticism toward newtechnologies, lack of capital, lack of infrastruc-ture for effective input distribution, and lackof agricultural and forestry extension servicesto accelerate the diffusion of new technologies.Before new technologies are introduced, an-thropological studies are needed to define thecurrent practices, including what rewards peo-ple are getting, what shortfalls they are ex-periencing, and what benefits they expect fromtechnology improvements. Both technicalagents and local residents need to understandthe incentives for change. Residents must beconvinced that the benefits will be what theywant if their cooperation is to be gained.

Inducements that can improve the quality oflife for farmers living in upland watershedareas and encourage shifting cultivators toadopt more stable agriculture practices in-

Ch. 10—Forestry Technologies to Support Tropical Agriculture Ž 237

elude: compensatory payments to farmers ex-cluded from upland grazing areas; timely pro-vision of inputs such as improved seeds, fer-tilizer, and credit; construction of improved ac-cess roads and feeder tracks; and the provisionof social services, such as improved water sup-plies, schools, and health clinics. Such socialmeasures, on the other hand, can have adverseeffects unless combined with rigorous exclu-sion of people and livestock from the steepestslopes. Improved amenities may attract largerpopulations into areas of critical hydrologicalsensitivity.

Constraints and Opportunities

Upper watersheds tend to be misused be-cause destructive land-use systems usualIy givethe greatest profit in the short term to the localpopulation. The solution to this problem neces-sitates: 1) developing methods of land use thatare more profitable to the local community andat the same time give appreciably better con-trol of water flows, and 2) testing the new tech-nologies and getting them adopted by the localcommunity. New systems that minimize eco-logical damage will be accepted willingly only

238 ● Technologies to Sustain Tropical Forest Resources—

if people can see that it will maintain or in-crease their standard of living without an in-crease in the risk of crop failure.

The key issue in watershed management isnot the construction of physical structures butthe need to provide people with improved land-use alternatives. Therefore, a high proportionof total watershed project investment shouldbe devoted to farming systems and institutionalcomponents rather than to soil conservationstructures or infrastructure.

The additional labor and capital costs oftenincurred by new resource conserving systemsare a major constraint to watershed manage-ment. Furthermore, farmers in the upperreaches of river systems generally do notaccept responsibility for damages their landuse may cause to farmers in the lower reaches.Conversely, lowland farmers rarely considerthat they have a duty to help finance uplandfarmers to adopt better systems of land use.Watershed management projects usually havebeen designed to benefit people in the more fer-tile lowlands and have neglected those in theuplands whose lives are being affected moredirectly. This implies that some of the benefitsgained downstream should be transferred up-stream through taxes or perhaps user fees onirrigation water or hydropower.

Finally, there are several important un-knowns regarding the hydrology of tropicalwatersheds. There is a dearth of first-handresearch evidence in the Tropics documentingthe quantitative relationships between variousland uses and their effects on watershedhydrology (20).

The techniques for measuring and predict-ing tradeoffs of different management ac-tions—e.g., grass cover versus tree cover—arenot well developed. For moist climates, treesmay be the best cover; for dry climates, grassesmay be the best cover if fire and grazing con-trol are practical. But for much of the Tropics,the choice is not clear. If more water rushesoff grass-covered surfaces, less will be absorbedinto the ground. Therefore, improved fieldmethods for diagnosis and interpretation ofwatershed hydrology problems are needed toimprove management decisions. The interac-tions of the many variables are too complex toexpect neatly classified prescriptions for water-shed management. Some basic measurementcould be included in all major projects that leadto changes in land use in order to build a moreadequate data base for predicting outcomes.

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