Reforestation of Degraded Lands

Sustaining Tropical Forest Resources:Reforestation of Degraded Lands

May 1983

NTIS order #PB84-104041

I SU~;rAIINII\JG TROPICAL RESOURCES

'#l' -.----\~ :::.--

Library of Congress Catalog Card Number 83-600533

For sale by the Superintendent of Documents,U.S. Government Printing Office, Washington, D.C. 20402

Deforestation has claimed half of the world’s original tropical forest lands. Theresult has been a decline in the land’s inherent productivity, with serious repercus-sions on human welfare. One solution to this vast problem is reforestation. Morespecifically, tree planting on degraded lands can help restore land productivityas well as provide wood for building materials, fuel for cooking, and fodder forlivestock.

This background paper is designed to provide the U.S. Congress with an over-view of some reforestation technologies and their possible beneficial and adverseimpacts. It also discusses the constraints and opportunities for the introductionof these technologies in such activities as timber and fuel production, watershedprotection, and agroforestry.

This paper is part of OTA’s forthcoming assessment Technologies To SustainTropical Forest Resources, A concurrent background paper, Sustaining TropicalForest Resources: U.S. and International Institutions, will focus on the role ofvarious institutions in developing and implementing technologies to sustain tropicalforest resources. These analyses form the main part of OTA’s response to the generalrequest of the House Committee on Foreign Affairs and the Senate Committee onEnergy and Natural Resources, and supported by the Subcommittee on Insular Af-fairs of the House Committee on Interior and Insular Affairs and the Subcommit-tee on Environmental Pollution of the Senate Committee on Environment and Pub-lic Works.

This paper was authored by OTA analysts Susan Shen and Alison Hess. OTAalso wishes to acknowledge the tropical forest resources advisory panel and ex-ecutive agency liaisons who reviewed this document and contributed technical in-formation to the OTA staff.

. .I l l

Leonard Berry, Panel ChairmanCenter for Technology, Environment, and Development

Eddie AlbertConservationist

Hugh BollingerDirectorPlant Resources Institute

Robert CassagnolTechnical CommitteeCONAELE

Robert CramerFormer PresidentVirgin Islands Corp.

Gary EilertsAppropriate Technology International

John EwelDepartment of BotanyUniversity of FZorida

Robert HartWinrock International

Susanna HechtDepartment of GeographyUniversity of California

Marilyn HoskinsDepartment of SociologyVirginia Polytechnic Institute

John Hunter*Michigan State University

Norman JohnsonVice President, North Carolina RegionWeyerhaeuser Co.

Jan LaarmanDepartment of ForestryNorth Carolina State University

Clark University

Chuck LankesterU. N. Development

Robert Owen

Program me

Chief Conservationist (retired)Trust Territory of the Pacific Islands

Christine PadochInstitute of Environmental StudiesUniversity of Wisconsin

Don PlucknettCGIARWorld Bank

Allen PutneyE C N A M PWest Indies Lab

Jeff RommDepartment of ForestryUniversity of California

Richard E. SchultesHarvard Botanical MuseumHarvard University

John TerborghDepartment of BiologyPrinceton University

Henry TschinkelRegional Offi”ce for Central American ProgramsAgency for International DevelopmentU.S. Department of State

“ Resigned in ]u1}I 1982.

iv

OTA Tropical Forestry Staff

H. David Banta, Assistant Director, 07AHealth and Life Sciences Division

Walter E. Parham, Program ManagerFood and Renewable Resources Program

Susan Shen Alison HessChris Elfring Bruce Ross-Sheriff

Administrative Staff

Phyllis Balan, Administrative Assistant

Nellie Hammond Carolyn Swarm

OTA Publishing Staff

John C. Holmes, Publishing (lfficer

John Bergling Kathie S. Boss Debra M, Datcher Joe Henson

Doreen Foster Linda Leahy Donna Young

Contents

Chapter1. Introduction and Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Z. Reforestation Technologies

3. Constraints and Opportunist

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Appendix A: Commissioned Papers and Authors . . . . . ~` . . . . . . . . . . . . . . . . . . . . . . .

Appendix B: Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Approximately 2 billion hectares (5 billion acres) of tropical lands are in variousstages of degradation and have, in theory, potential for reforestation.

Most manmade reforestation is done with imported species. Many native trees,more familiar to local people, have untapped potential for reforestation.

Tree plantations using only one species are widespread, Little effort is being madeto develop technologies for multiple-species reforestation,

Selection and breeding of superior trees in temperate zones have gradually pro-duced varieties adapted to specific site conditions that give as much as 50 per-cent yield gains. However, such work is just beginning in the tropics.

New cloning techniques can produce millions of “supertrees,” but they increasethe risk of failure because of reduced genetic diversity.

Organized programs of seed collection, processing, certification, storage, anddistribution are needed to develop the seed quality and quantity necessary forlarge-scale reforestation,

Bacterial and fungal inoculants can increase tree survival and growth, especiallyon degraded lands. Many of the needed inoculants are not yet commerciallyproduced,

Reforestation is most likely to be successful when programs are designed to pro-vide what local people want. In many cases, this means the creation of variouskinds of incentives for local participation.

New technologies have the potential to reduce the costs of reforesting degradedlands; however, better methods are needed to measure important but indirectbenefits in order to justify the reforestation investment.

. . .Vlll

Chapter I

Introduction and Background

Contents

PageIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Definition of Degraded Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Tropical Soils and Climates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Scope and Causes of Land Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Reclamation Using Trees. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table

Table No.I. Tropical Lands Recently Undergoing Severe Desertification

List of Figures

FijweNo.

. . . . . . . . . . . . . . . . .

l._Tropical Forests and Woodlands, for the purpose of the Report, are Located atLatitudes South of 23.5° N and North of 23.5° S, and at OtherFrost-Free Localities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2. The Role of Forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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410

Introduction and Background

INTRODUCTION

Eleven million hectares (ha) of the world’sremaining tropical forests are converted toother land uses or to wasteland each year (33).About half of the Earth’s original tropical forestland has thus been altered. Deforestation canbe beneficial where cleared tropical land cansustain agriculture. Under available farmingtechnologies, however, many remaining tropi-cal lands cannot sustain agriculture and aresoon abandoned or converted to less produc-tive uses. Often, forests cannot regrow natural-ly on these degraded lands.

Tropical nations* (fig. 1) have about 650 mil-lion ha of cropland and nearly 2 billion ha ofland in various stages of degradation (33,114).Those regions with rapidly growing popula-tions—Asia, Central America, North Africa,and the heavily populated parts of East andWest Africa—need productive land most des-perately, yet have the most rapid deforestationand extensive areas of degraded land. In manyof these places, firewood has become so scarcethat certain foods requiring cooking have beeneliminated from the diet. People must use cropresidues and dried dung for fuel, which robsthe soil of organic matter and nutrients and ac-celerates erosion. Soil eroded from degradedlands fills riverbeds and reservoirs, increasingthe severity of floods and causing water scar-cities.

The best solution for stopping this trend ofland degradation is to prevent inappropriateland-use practices on forested lands. Wherethis is not possible, reforestation is one way toimprove the productivity of many degradedlands and provide useful products for the peo-ple. Trees provide wood, fuel, food, fodder, and

*In this b,~(.k~round paper, tropical lands include all lands lo-(:ated at Iatltudes south of 23.5 N and north of 23.5 s.

other uses.of tropical

Trees protect soil from the effectsheat, rain, and wind. Soil tem-

peratures are lower under tree canopies, per-mitting reaccumulation of organic matter thatrestores soil structure and microbiota and en-hances moisture- and nutrient-holding abilities.Bacteria on the roots of some trees produce ni-trogen fertilizer, while fungi on tree roots canconvert soil minerals to useful forms. In dryareas, trees can help to prevent the rise ofsaline ground water (92). Where surface soilsare dry or infertile, deep tree roots can tap un-derground reservoirs of nutrients and waterand bring them to the surface.

In recent years, reforestation efforts have in-creased. Of the approximately 11.5 million haof planted forest in 1980 in the tropical nations,some 40 percent have been planted since 1976(33). About 60 percent of this was planted forindustrial purposes (lumber, veneer, pulpwood,etc.). The other 40 percent was nonindustrial(fuelwood, watershed protection, etc.). Whileit is not known how much of this planting oc-curred on degraded land and how much oc-curred on recently cleared primary forests, itis probable that a 1arge and increasing propor-tion of the reforestation, especially nonindus-trial planting, is occurring on degraded sites(37).

This background paper discusses techniquesto reforest tropical lands and gives special em-phasis to degraded lands and community-ori-ented forestry. It does not address methods tomanage existing forests, nor does it focus onpublic policies or institutional mechanisms tosustain tropical forests. Those issues are cov-ered in a forthcoming OTA report, Technol-ogies To Sustain Tropical Forest Resources,and in another background paper, U.S. and in-ternational Institutions.

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--Tropic of Cepflcom

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Figure 1.-Tropical Forests and Woodlands, for the Purpose of the Report, Are Located at Latitudes South of 23.5 0 N and North of 23.5 0 S, and at Other Frost·Free Localities

North AUanlic Ocean

-;I

Ch. l—introduction and Background ● 5

BACKGROUND

To understand the constraints on existing re-forestation techniques and the potentials ofnew ones, it is first necessary to define landdegradation, briefly describe tropical soils andclimates, and discuss the causes of land deg-radation and benefits of reforestation.

Definition of Degraded Lands

Degradation of tropical land is a physical,chemical, and biological process set in motionby activities that reduce the land’s inherent pro-ductivity. This process includes acceleratederosion and leaching, decreased soil fertility,diminished natural plant regeneration, dis-rupted hydrological cycle, and possible salini-zation, waterlogging, flooding, or increaseddrought risk, as well as the establishment ofweedy plants that displace more desirable plantspecies, Evidence that the degradation processis advancing includes, for example, a reduc-tion in the water-holding ability of the soil, adecrease in the amount of soil nutrients avail-able to plants, a reduction of the soil’s abilityto hold nutrients, or soil compaction or surfacehardening.

This definition implies a strong interrelation-ship between inappropriate land-use practicesand land degradation. In some places degrada-tion is manifest (e. g., erosion and desertifica-tion), whereas in others it is inferred (e.g.,declining crop yields).

Tropical Soils and Climates

Although the chemical, physical, and bio-logical processes that occur in the tropics arethe same as those elsewhere in the world, therates often are accelerated. Tropical air, soil,and water temperatures are higher; rainfall ismore intense and erratic; and the growing sea-son is longer than in temperate parts of theworld. These factors affect tropical forests andtheir soils. Further, they can place severe con-straints on certain land uses. Although detailedsoil descriptions are beyond the scope of this

report, * a simple but useful breakdown of trop-ical areas divides it into three types: 1) hot, wetlands, 2) arid/semiarid lands, and 3) mountain-ous lands.

Most tropical soils on hot, wet lands have sig-nificant fertility problems. Year-long high tem-peratures and high rainfall combine to accel-erate the removal of nutrients needed by plantsfrom rock materials and soil mineral particles.The residual minerals tend to be composedmostly of aluminum, silicon, iron, oxygen, andwater—a chemical composition so restrictedthat many food or tree crops will have stuntedgrowth or will not survive. An estimated 2 per-cent of the soils of hot, wet lands, if clearedof vegetation, will irreversibly harden on dry-ing (119), severely limiting reestablishment ofany vegetation (67).

In arid/semiarid lands, soil nutrients neededby many plants become available to plants withsufficient water (16). However, if most of thewater evaporates from the soil surface ratherthan percolating down, dissolved solids or saltscan accumulate at or near the land surface inconcentrations that many plants will not toler-ate (43).

Mountainous lands** are cooler than theother two categories and exist in both wet anddry climates. Because they have steep slopes,their soils are easily eroded. Much of the rain-fall in the wetter regions runs off the land sur-face rather than percolating into the ground.Consequently, soils in mountainous lands arelikely to be rocky and thin, except perhaps onthe lower slopes (16),

*See Van Wambeke (1 19) and Fripiat and Herbillon (36) formore detailed information. These are good references on soilsof the hot wet tropics. They not only contain the commonly citedinformation on agriculture, soil names, etc., but also provide dis-cussions of mineralogical and chemical processes.

* *Elevated areas throughout the tropics typically from 750meters and abet’e.

6 ● Background Paper #1: Reforestation of Degraded Lands

Photo credit. B C Stone for the National Academy of Sciences

Severely degraded lands on Guam which were once covered by tropical forestsErosion has uncovered large expanses of infertile soil

Photo credit OTA staff

Barren landscapes on islands along the south coast of China reflect deforestationthat occurred hundreds of years ago

Ch. l—/ntroduction and Background ● 7

Scope and Causes ofLand Degradation

In much of the open woodlands of arid andsemiarid areas, overgrazing and repeated fireshave converted the vegetation to a degradedfire climax stage. Consequently, soils becomedry and little woody regeneration occurs. Fire-tolerant vegetation—often unpalatable to ani-mals—persists, leading to a desert-like state. To-day, there are few undisturbed woodlands orsavannas in these regions. An estimated 20.5million hectares (ha) of tropical arid lands, anarea about the size of South Dakota, becomedecertified every year. To date, an estimated1.56 billion ha of tropical land have undergonedesertification (table I).

Desertification occurs in the savanna regionof North Africa as well as in the savannas ofsouthern tropical Africa and northeast Brazil.In the Sudan and elsewhere in North Africa,the populations of grazing animals—includinggoats, sheep, cattle, and camels—number in themillions and their grazing intensity has severe-ly impaired natural regeneration of forests andforage (28), Consequently, people have had torange farther in search of fodder for theiranimals and wood for cooking and heating(131).

Forest degradation and loss under the rainyand seasonal environments may not be so se-vere as under the arid and semiarid environ-ments, but the effects on people are similar.There are approximately 156 million ha oftropical moist forest, 181 million ha of forestfallow, and 84 million ha of deforested water-sheds available for reforestation (131 ). Whenareas cleared by agriculturalists are exposedto abundant rainfall, erosion, and leaching, soil

Table 1 .—Tropical Lands Recently UndergoingSevere Desertification (million hectares)

Region Total decertified area

Latin America. . . . 701,8Africa, ... . . . . . . ... . . 685.0I n d i a a n d P a k i s t a n . 170.0

Total . . . . . . . . . . . . 1,556.8SOURCE United NatIons, UN Conference on Desertification: Round-Up, Plan of

Action and Resolutions (New York United Nat Ions, 1978)

productivity is greatly decreased. After 1 to 5years, the land typically is abandoned by farm-ers who move on to other areas. The land thenreverts to secondary forest, vines, brush, orgrasses of low nutritive value. Land abandon-ment is caused by decreasing crop yields andincreasing weed control problems (57). Nor-mally, these farmers (shifting cultivators) allowfallow periods of 10 to 15 years, thus givingenough time for soils to recuperate some pro-ductivity, However, in a growing number ofplaces, increased population pressures lead toshortening of these periods. Food productionis then greatly decreased, leading to evenstronger pressures to clear more forest. Sucheffects of acute population pressure are evidentin Haiti, El Salvador, and parts of the Philip-pines and Indonesia (131). Detailed descrip-tions of tropical agriculture and its effect onsoils include: Laudelout (71); Nye and Green-land (88); Jurien and Henry (60); Watters (123);Sanchez (104); Lal and Greenland (69].

Population growth rates in tropical countriesare the world’s highest. Growing numbers andrising aspirations lead to more than propor-tional increases in the demand for food, fuel,fodder, and building materials (15). Populationgrowth also requires increased land for ur-banization and village expansion, energy pro-duction, and transportation (14).

With few exceptions, such as the river valleysof West Africa where river blindness is beingeradicated, most of those lands that can sus-tain stable agriculture probably have beencultivated. Remaining unused lands are thosealready degraded, or those too infertile for con-tinuous farming without constant infusion ofhigh-cost inputs such as commercial fertilizer.Without these inputs, the land becomes suscep-tible to degradation, thus reducing the standardof living (49,108).

In recent years, some developing countrieshave been planning and encouraging move-ment of people, usually into sparsely occupiedVirgin tropical forests, Two examples areBrazil’s planned colonization of the AmazonBasin via the Transamazon highway and Indo-nesia’s colonization of its outer islands (49,108).

In both cases, people are moved between re-gions that are geographically and geologicallydifferent and thus they are ill-equipped to copewith the new environment. Consequently, in-appropriate land use practices have led to de-creased crop yields. Forest clearing exposedthe lands to heavy erosion and depleted thesoil’s nutrient supply, leading to land degrada-tion and to indebtedness and landlessness forthe people.

The expansion of lands under cultivation willcontinue, given the rising pressures. Morelands will become degraded and subsequentlyabandoned. To break this cycle, some of thesedegraded lands can be reclaimed via reforesta-tion. Tree planting of degraded lands is not apanacea to deforestation or inappropriate landuses. Some degraded lands will be difficult and

some may be impossible to reclaim. In addi-tion, reforestation of degraded lands may notbe so profitable, in financial terms, as reforesta-tion of rich, fertile lands. However, in manycountries, fertile sites are reserved for agricul-tural activities. Given the dwindling amountof good lands and the increasing demands forforest products, it is necessary to consider allalternatives. Reforestation is an alternative thathas the potential to rehabilitate the degradedsoils and provide many goods and services forindustrial and local needs.

Reclamation Using Trees

For degraded sites it is often advantageousto plant trees because of their ability to usewater and nutrients inaccessible to plants with

shallow roots and because they supply a mul-titude of products: wood, fuel, fodder, andothers. Moreover, a tree canopy acts as a buf-fer against the direct impact of raindrops onthe soil. The litter and humus layers underlyingthe forest absorb moisture, allowing water toinfiltrate the ground and recharge the groundwater supply (92). Trees, by shading the soil,reduce soil temperatures and thus promote ac-cumulation of organic matter and retard possi-ble soil hardening,

The presence or absence of organic matterin any soil is an important factor in the soil’sproductivity. Soil organic matter is importantto soil productivity because it:

● contributes to the development of soil ag-gregates, which enhance root developmentand reduce the energy needed to work thesoil;

• increases the air- and water-holding ca-pacity of the soil, which is necessary forplant growth and helps to reduce erosion;

● releases essential plant nutrients as itdecays;

• holds nutrients from fertilizer in storageuntil the plants need them; and

● enhances the abundance and distributionof vital soil biota (90).

Ch. 1— Introduction and Background ● 9—

Soils under forest cover often have high or-ganic matter content. Land-use practices thatjeopardize the soil’s organic content thereforecan have adverse effects on successful}’ refor-esting degraded lands.

The living network of roots near the surfaceof forest soils provides mechanical support forsteep slopes; this root network is the main con-tribution to slope strength and prevention oflandslides (100). Consequently, trees are par-ticularly valuable for watershed protection andfor arresting desertification in areas of mov-ing soils (e. g., sand dunes). Some trees act assoil improvers as well as soil protectors.Leguminous trees and forbs have the capacityto enrich soil with nitrogen. Legume trees havenutrient-rich leaves which can be used as fod-der or mulch (80,81).

There are many reasons for planting trees.Provision of goods for household and industrialuse (see fig. 2) is equally as important as reha-bilitative factors. For local needs, a tree specieswith several attributes or a mixture of tree spe-cies can be planted to obtain multiple benefits—e. g., abilityable for fuelfor fodder.

to enrich soil fertility, wood suit-and poles, and nutritious leaves

10 . Background paper #1: Reforestation of Degraded Lands

Figure 2.— The Role of Forests

<.

CatchmentControlled runoff, water

Y protectionr I supplies, trrlgatlon, soil

4 fertllily, oxygen

Recreation, tourism,* <

Ecological effectsEcology and wild national parks, protection

— - Ilife conservation of endangered species of

flora and fauna

Windbreaks, shelter belts,dune fixation, reclamationof eroded lands

— Fuelwood and a Cooking, heating, andcharcoal household uses

Shifting cultivation, forest— Agricultural uses r 1 grazing, nitrogen fixation,

mulches, fruits and nutsL

Housing, buildings,- Building poles L construction, fencing,

furniture

IIndigenous consumption

Plt saw!ng and Jolnery, furniture, con-sawmilling struction, farm buildings

i

Ropes and string,- Weaving materials baskets, furniture,

4 furnishings4

Serlculture, aplcul-ture, erlculture

Silk honey, wax Iac

{Carving, Incense,chemicals glassmaking I

L 8 t J

Naval stores tannin,Gums, resins.. turpentine, distillatesand OIIS resin, essential oils

&

Reduction agent for steel-9 Charcoal r 1 making, chemicals, poly

vinyl chloride [PVC) dry cells6

I Transmission polespitprops 1

I Industrial uses l—I 1 T Lumber joinery, furniture 1

Sawlogst

packing. ‘shlpbuildingmining, construction sleepers I* d h

4 Veneer logs H Plywood, veneer, furniture,containers. construction I

1 I 1 J

Newsprint. paperboard.prlntlng and writing paper

- Pulpwood . containers, packagingdissolving pulp, distillates

●

textiles and clothing

ResiduesI

Particle board fiberboardAwastepaper

SOURCE World Bank 1978

Chapter 2

Reforestation Technologies

Contents

What To Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Native. Exotic Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Monoculture. Polycuhure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Single-Purpose v. Multipurpose Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Genetic Improvement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Planting Materials .. ... ... ~.t.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Seed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Nursery Planting Stock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Direct Sowing . . . . . . . . . . . . . . . . . . . . . . t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Transplanting Wildlings and Stumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Land Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Manual v.Mechanical Clearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Soil Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Tree Planting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Repairing Eroding Watersheds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Reforesting Unproductive Grasslands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Arid and Semiarid Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Saline/Alkaline Lands . . 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

protection and Maintenance of Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Protection From Livestock Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Weed Control.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Local Participation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Reforestation Using Combinations of Trees With Agricultural Crops . . . . . . . . . . . .

List of Tables

Table No.2.

3.4.5.6.

Suitability of Variousin the Tropics . . . . . .Comparison Between

Types of Nursery. . . . . . . . . . . . . . . . ,.,... . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Container and Bare-Rooted Methods of Raising Seedlings

Vegetative Propagation Techniques Used With Tree Species . . . . . . . . . . . . . . . . .Possible Candidates for Aerial Seedings in Developing Countries . . . . . . . . . . . . .A Selection of Tree Species Tolerant of Saline and Alkaline Conditions . . . . . . .

Figure

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1717182425

262627

2828293133

36363636

38

Page

1820212635

Figure No. Page

3. Production of Nursery Stock in the Tropics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Chapter 2

Reforestation Technologies

Reforestation, for the purposes of this paper,refers to the planting of seeds, plants, or partsof plants to establish trees. This definition in-cludes afforestation. * This section of the paperdiscusses various preplanning considerations,the application of various technologies on dif-ferent types of degraded lands, and alternativetechnologies to maintain the newly restoredsite. Both new and promising technologies, aswell as conventional techniques, are described,

Although a discussion of natural regenera-tion” * of forests is outside the scope of thisbackground paper because it requires little hu-

Before a reforestation effort is initiated, adecision must be made as to what to plant. Thechoice of tree species depends on the site tobe reforested. In this case, “site” includes notonly the physical environment but also socio-economic factors—especially the needs of landusers. Trees selected to reforest degraded landsmust be able to thrive on open lands, competewith aggressive weeds, and withstand stress(e.g., drought, fire, low fertility). It is especial-ly beneficial if the species can add nitrogen tothe soil and provide products that serve theneeds of local communities.

The debate whether to use native or exotictree species, to plant in monoculture orpolyculture, and to select single-purpose ormultipurpose trees continues. Meanwhile, sev-eral factors may influence the selection.Among them are the objectives of reforestation,availability of seeds, and the level of costs(labor, cash, and risk) associated with reforesta-tion alternatives, The primary reason for thekinds of reforestation addressed in this back-ground paper is to restore degraded lands and

man manipulation, it is a technology worthyof further investigation and research. Silvicul-tural treatments of naturally regenerated for-ests to encourage and enhance natural repro-duction have great potential for preservationof genetic resources and may be less costlythan plantations (122). Preliminary studies indi-cate that productivity of naturally regeneratedforest plots can be equal to or greater than theproductivity of plantations after 40 years (59),The results suggest that plantations may nothave an advantage over natural regenerationin the long term. However, few techniqueshave been developed to manage native tropicalforests, and those few attempts have concen-trated mainly on the tropical rain forests andmoist deciduous forests (111).

PLANT

to produce products—e.g., food, fuel, fodder,or commercial timber—to meet the needs of thepeople.

Native v. Exotic Species

Most large-scale tropical plantations to pro-duce industrial timber use exotic species. * Themost commonly used genera are 1% us, Euca-lyptus, Gmelina, Tectona, Terminalia, Cupres-sus, Cunninghamia, and Araucaria. S o m elesser known genera such as Cedrela, Triplo-chiton, Anthocephalus, Aucoumea, Albizia,and Agathis also are gaining popularity. Mostof these genera, though indigenous to the trop-ics, are planted as exotics (37).

Despite objections that exotic species aresusceptible to increased disease risk, they havebeen used exclusively in plantings in thetropics. This may be because there is much ex-perience, information, and research on exotics,especially on Pin us, Eucalyptus, and Tectona.There are arguments for and against the wide-

*Trees that are not nat i~rc to a locale.

13

14 ● Background Paper #l: Reforestation of Degraded Lands

spread use of exotic species. Proponents citetheir initial reduced susceptibility to native in-sects and diseases as an advantage, However,exotic species may be more susceptible to seri-ous damage if native pathogens and pests adaptto the new hosts, since the exotics are unlike-ly to have evolved resistance to these orga-nisms.

The use of native species—ones that grownaturally in the local region—in plantations hasbeen largely ignored. The reasons for this varyfrom lack of familiarity with many tropical treespecies to lack of seed supplies, and the some-times slower growth rates of native species,The latter is a common argument for using ex-otics over native species (37,131,135). However,while this difference may occur where rainfallis above 1,5oO millimeters (mm), growth of ex-otics and native species usually are similar inthe arid and semiarid parts of Africa (126).

Arguments supporting reforestation usingnative species are varied. First, native speciesare adapted to the local environment and thusmay be less susceptible to stress, serious dis-ease, and pest damage. Local people are morefamiliar with their native plants and have moreuses for them (54), Similarly, the timber ofnative species is likely to be known to localwood-using industries. Further, use of nativetrees contributes to the conservation of nativeflora and fauna (29).

Monoculture v. Polycuhre

The use of a single species in forest planta-tions is known as monoculture. Monocultureplantations may be more susceptible to diseaseand pest outbreaks. Some diversity can beachieved by alternating species in blocks ofland being planted or by alternating differentgenetic varieties of the same species, Thismethod should prevent pests that develop andmultiply in one plantation block from spread-ing rapidly to other blocks of trees having thesame genetic makeup (135),

Multiple species (polyculture) plantationsare, in theory, better able to mimic the natural

forest, yield a greater variety of products, andare less susceptible to pests than are monocul-ture. Interplanting legume (nitrogen-fixing)tree species with other commercial tree speciesmay reduce the amount of fertilizer requiredafter successive rotations. In experimentalplantations, Indonesians are interplanting Cal-liandra with Pin us merkusii and with Eucalyp-tus deglupta to yield firewood for local use,Calliandra also shades trees such as Agathisloranthifolia, which require shade initially forbetter growth (83).

Yet little actual experience has been gaineddealing with polyculture plantations either atthe industrial scale or in village forests (131).Only recently have projects been establishedwhere mixtures of species have been plantedfor a variety of end uses (e.g., GTZ, IDRC, andUSAID projects in the Sahel). Areas of mixedplantations are beginning to be established inthe social forestry projects of Asia, especiallyIndia and Nepal, Even in those projects, infor-mation is lacking on the optimum species mix-ture and spacing. The management of mixturesof tree species for production is biologicallycomplex, especially for more than two species.It becomes even more difficult where multipleproducts are extracted from multiple speciesunder multiple harvesting regimes. However,perceived benefits of polyculture planting,

Photo credlf. COMALCO for NAS

Polyculture: African mahogany (Khaya species) plantedbetween Leucaena leucocephala trees on highly aluminoussoil in Weipa, North Queensland, Australia. Leucaena is

being tested as a nurse crop for mahogany

Ch. 2— Reforestation Technologies • 15————

especially in the context of social forestry,make them worthy of further investigation.

Single-Purpose v. Multipurpose Trees

Forest plantations in the past served in-dust rial purposes and thus grew only one prod-uct, such as sawtimber or pulpwood. Now,with an increasing demand for food, fuel, andfodder, plantations are needed to serve a varie-ty of objectives, Thus, the use of multipurposetrees is becoming increasingly important, es-pecially on degraded lands where populationpressure is often high. Acacia albida, amultipurpose tree, bears leaves at the begin-ning of the dry season, thus providing shadewhen most other trees are bare. It also yieldsedible seed pods at a time when little other fod-der is available. The tree enhances soil fertili-ty because it fixes nitrogen and provides leafmulch, and it can be used as firewood (82). A.albida is just one of more than 1,000 speciesof the genus Acacia (84]. Other multipurposetrees exist that perform equally well and holdgreat promise for reforestation. Various listsof these promising species are available (44,79,80,83,84,85,118,1 25).

The family Leguminosae deserves special at-tention in the process of selecting trees for re-forestation. Legumes are among the first to col-onize newly cleared land. Acacia albida, men-

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Multi purpose trees such as Sesbania grandiflora canprovide firewood, fodder, food, and green manure and

hold promise for reforesting eroded wastelandsthroughout the tropics

tioned above, is a legume. Its kin, Acacia man-gium, outperforms other species on degradedlands in Malaysia. Wood of this species haspotential for sawtimber, veneer, furniture, fire-wood, pulp, and particle boa rd. Its leaves canbe used as forage for livestock (85). The foliageof species such as Calliandra is readily eatenby cattle and goats; its flower provides rich nec-tar to produce Calliandra honey (84). Man}other tropical legumes exist whose potentialsare unknown.

Little is known of the variability in growthand performance of multipurpose tree species.Variation is related to habitat so that eachplanting site should be tested with geneticallydifferent varieties of the same species. Such ef-forts are under way. The National Academyof Sciences (NAS) is designing and implement-ing international trials of tree species for theSahel and of multipurpose tropical tree speciesfor many grantee institutions. Both the Inter-national Council for Research in Agroforestr} r

(ICRAF) and the Commonwealth Forestry In-“stitute are cooperating with NAS in preparingmanuals for evaluation of multipurpose spe-cies. But even when correct species and pro~

r-enances are known, there is still a major gapin the knowledge of silvicultural techniques formultipurpose tree plantings. Here, little infor-mation is available, and no research guide ex-ists, Despite these obstacles, multipurpose treesmerit special consideration because of theirmultiplicity of likely benefits.

Genetic Improvement

Plant breeding has been responsible for abouthalf of the spectacular gains in agriculturalcrop yields accomplished in the past threedecades. The application of genetic science toforestry lags many decades behind agriculture,partly because it takes a longer time to breedtrees than agricultural crops. However, treebreeding programs in industrialized nationshave already achieved important productivitygains–l0 to 20 percent in first generation and35 to 45 percent in second generation seedorchard progeny-for industrial timber plan-tations (87). First genetic selections haveyielded gains of as much as 50 percent in some


energy plantations (97). Tree breeding pro-grams could greatly accelerate genetic im-provement of trees, especially tropical trees,and forestry yields from degraded land sitescould increase.

Most reforestation projects in the tropics useseeds without testing them to see whether theyare genetically appropriate for the project’s siteconditions. Since most tree species used inreforestation are found over broad geographicranges, different races within the same specieshave adapted to different environments. Thus,a species’ suitability to a particular site canvary depending on the race used. A well-estab-lished technique matching races with sites iscalled provenance* testing. Seeds of the de-sired species are collected from various sites(provenances) and tested at the site to bereforested or at a site with a similar environ-ment.

Once the best provenance has been identi-fied, several options are available to obtainplanting materials, Seeds from the desiredprovenance sometimes can be purchased. Al-ternatively, individual trees from the prov-enance test can be selected as parent material.Once the best individuals have been identified,they can be used to establish seed orchards orto produce rooted cuttings for planting mate-rials. This ensures that only seeds and seed-lings from superior trees are used in the refor-estation program. Another technique is to usesuperior trees from an environment similar tothe reforestation site to establish a seed orchardwithout the provenance testing. If the desiredspecies already grows on the reforestation siteand if superior trees have not been eliminated,then it is possible to obtain planting materialsadapted to the site from those trees. Where thisis feasible, it is probably the fastest and leastexpensive approach.

These tree improvement and selection tech-niques have been successful for reforestationon degraded tropical lands. For example, Euca-lyptus grandis generally does not grow well onthe steep, eroding, and phosphorus-deficientsoils of Andean slopes in Columbia. By select-

*Testing populations of the same species to study their per-formance under a range of site and climatic conditions.

ing trees from early plantings that did growwell on such sites to establish a seed orchard,an adapted race for the degraded sites has beenproduced (135),

Conventional provenance testing is a majorundertaking. For proper statistical analysis,hundreds of trees from each seed source areplanted in replicated blocks and grown tomaturity. The process generally takes so longthat the original seed source may be unavail-able by the time results are available. When thathappens, the test plots must be developed asseed orchards, further prolonging the process.This usually takes too long to accommodate anindividual reforestation program, Many prove-nance tests do not yield results because ofpremature termination of the projector depar-ture of the investigator. Therefore, provenancetesting must be carried out by established insti-tutions that can maintain long-term programs.

The potential to shorten the time needed fortree improvement is increasing as new tech-niques are being tested. Tissue culture (dis-cussed in the following section) can rapidlymass-produce clones of chosen individualsfrom a provenance test. The clones can thenbe tested for particular microsites or outplantedat the reforestation site. The establishment ofinternational networks of cooperating scien-tists to collect seeds or planting material andto record environmental data for each parenttree can reduce the number of provenances tobe evaluated for each test. Another new tech-nique, where many provenances are plantedin one stand (single tree randomized plots), al-lows the testing of many more provenanceswithout a corresponding increase in budget orpersonnel. And the propagation of clones en-sures that the provenance with the exact genet-ic materials is used, thus allowing more typesto be tested, The U.S. Forest Service, in experi-ments with Eucalyptus in Florida, used singletree randomized plots and cloning to shortenthe time for screening of appropriate prove-nances (38). These techniques have not beenused in reforestation of degraded tropicallands. Before that can be done, pilot-scale im-plementation projects, ones having at least a10-year timespan for sufficient results to ap-pear, need to be initiated.

Ch. 2—Reforestation Technologies ● 1 7

PLANTING MATERIALS

Various techniques are used to propagate Seedtrees, Some propagation techniques have beenknown for centuries (e.g., direct seeding) and To reforest degraded lands, seeds of variousare available for implementation; others (e. g., species must be available in great quantities.tissue culture) are at various stages of develop- Today, supply falls short of need, The seedment or are undergoing refinement. (See fig. supply for species most commonly used in3 for schematic chart of production of nursery tropical, industrial plantations (pines, eucalyp-stock and table 2 matching nursery planting tus, Gmelina, teak) is adequate, although somestock with land classifications. ) valuable provenances are in short supply and

Figure 3.— Production of Nursery Stock in the Tropics

Product Ion ofpropagules a

Raising ofpropagules

I Seed 1 I Vegetative 1

1 <Seed bed IContainer Graft/ Tissue

bud culture

v

Transplant Containerizedbeds plants

Met hod

Type ofplanting stock

Container andmedium identical

(plastic, pulp, etc.)

I I

(Root pruning) RigidSoft container

filler withcontainer medium

Planting stock

[Piants incomplete Plants complete. I

1 \Tall plants, leaves Root & shoot With root bare Clay ballsstripped (Striplings) cut back (stumps) bail root (boulette)

● a .aA s t r u c t u r e (e g cutt (ng seed) t h a t p r o p a g a t e s a plant

SOURCE Evans 1982


Table 2.—Suitability of Various Types of Nursery Planting Stock for Reforestation in the Tropics—

Climatic conditions— .Type) of planting Lowland rain Montane Rain Dry/semidecidu- Areas of unreli- Arid areasyypepe,

site forest Forest ous forest able rainfall

Dense forest Tall, whole plants Tall, whole plants Potted stock or Potted stock,or strippings stumps stumps, strippings

Open exploited Tall, whole plants Tall, whole plants Potted stock or Potted stock orforest/line or strippings stumps stumpsplanting

Agricultural land/ Large, bare-rooted Small, bare-rootederoded land/ plants. Potted or mini pottedtaungya systems stock. Direct stock. Direct

sowing sowing

Clean weeded Small, bare-rooted ‘Small, bare-rooted,land or minipotted or mini potted

stock. Direct stock. Directsowing sowing

Areas with risk of Large strippings Large strippingsbird damage oranimal browsing

SOURCE J Evans (29)

their natural origins are threatened withgenetic impoverishment or extinction. Theseed supply for multipurpose, agroforestryspecies, on the other hand, is small. Organizedprograms of seed collection, extraction, stor-age, and distribution are needed to develop thequantity necessary for large-scale reforestation.

Seed storage of tropical tree species is a prob-lem. Tropical species show great variation intheir capacity to retain viability under naturalconditions. Many large-seeded species haveshort periods of viability; Swietenia seed isviable for only 6 weeks. Other species retaintheir viability only under certain conditions.Seed of Araucaria hunsteinii will die if allowedto dry out. Legume tree seeds must be kept dryand free from insect or rodent damage to re-tain their viability (29). Seed storage is thereforean important part of reforestation efforts.Many factors influence the longevity of seedin storage. Recently, some progress has beenmade in this area. Seeds of some tropical plantspecies can now be stored in liquid nitrogen (3).

Another problem exists regarding the trans-fer of seeds within a nation and international-ly because the records of seed source and ge-netic history are sometimes poor (17,58), Plansto control planting material (e.g., ref. 89) do notyet apply to tropical countries, and tree seed

—Potted stock. Potted stock.Root-pruned, Root pruned,bare-rooted bare-rootedstock, stumps. stock, stumps.Direct sowina Direct sowing

Potted or root- Potted or root-pruned, bare- pruned, bare-footed stock. rooted stock.Direct sowing Direct sowing

Large-potted Large-pottedstock or stumps stock or stumps

Robust-pottedstock (sowing)

Robust-pottedstock (sowing)

Robust-pottedstock

dealers generally sell seeds without adequateinformation regarding the place where the par-ent trees were grown. The use of poorly iden-tified seed often has made it impossible to tracethe origin of seed which produced a promis-ing stand meriting further trial or one of badform to be avoided, Full records of all forestseedlots should be made and copies should ac-company all seed distributions, Most impor-tantly, every shipment of seed should showhow the species was identified, where andwhen the seed was collected, and specific siteand stand information about the seed source(see ref. 29 for a sample certificate of seedorigin). Thus, the recipient will know the quali-ty and origin of a seedlot if problems developlater. International attention was drawn to thisproblem at a meeting sponsored by the Nitro-gen-Fixing Tree AssociationItaly, in September 1982. Itfocus of a meeting proposedheld in 1983 (74),

held at Bellagio,will also be theby ICRAF to be

Nursery Planting Stock

Seedlings

Growing seedlings in a forest nursery is thecustomary way of raising planting stock in thetropics. (See ref. 91 for sample technical man-

Ch 2— Reforestation Technologies • 19

ual on nursery practices. ] The two most com-mon methods of raising tree seedlings are:1) in open beds for bare-root planting, and2) in containers for seedlings to be planted withnursery soil around the roots.

Seedlings, in the past, were raised in openbeds and planted in the field bare-rooted. Thoseseedlings, however, were susceptible to desic-cation and survival was poor. Survival im-proved when seedlings were taken in individ-ual containers from the nursery to plantingsites with soil still around the roots. Container-ized seedling techniques have evolved from themethod of cutting into the nursery bed betweeneach seedling so that a cube of soil remainedattached to the roots (Swaziland bed system)to starting seedlings in the containers. Thetypes, sizes, and durability of containers varygreatly. Choice of container usually dependson cost and convenience, but containers oftenare bulky to transport because of the soil.

The various types of containers can be clas-sified according to their porosity:

●

●

●

impervious containers—metal, plastic, orother materials;semipervious or pervious containers—mostly paper based, not removed at plant-ing; andpre-filled containers—individual units ofgrowing medium (29).

The most commonly used container is the im-pervious type. Although most are plastic bagsor metal tubes, local materials can be used.Bamboo, wood veneer, and banana or palmleaves have been used widely in different partsof the world (32). For example, Paper IndustryCorp. of the Philippines uses waste veneersfrom peeling operations. The use of closed-bot-tom containers, however, can result in rootcoiling if the seedling is left in the tube too long.This can be avoided with more modern con-tainers that have an open bottom and are sus-pended above the ground. The roots self-prunewhen they come to the air below the contain-ers. See table 3 for a comparison of containerand bare-rooted methods. Also, see Tinus andMcDonaId (112), Venator (120), andTinus(113)

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Tree seedling containers in Hawaiian nursery, Roots growout of a hole i n the base of each container, a technique

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for more details on growing seedlings in con-tainers.

Vegetative Propagation

Another technique is vegetative propagation,the reproduction of planting stock without theuse of seed. Vegetative propagation has the ad-vantage of hastening production of geneticallysuperior plants and massive reproduction ofclones, assuring that the plants will all be ofthe desired genetic type. It has the disadvan-tage of higher risks because of lack of geneticdiversity, It also requires greater technical ex-pertise. Vegetative propagation is widely usedfor reproducing crop trees such as rubber, co-conut, tea, coffee, cocoa, and oil palm. Moredetailed trial work is needed to develop effi-cient operational systems for many tropical for-est species.

Methods of vegetative propagation includecuttings, air layering, budding, grafting, andtissue culture (see table 4 for a brief assessmentof each of the techniques). Rooted cuttings re-main the most popular method. Each year, sev-eral million Eucalyptus trees are propagatedfrom rooted cuttings in Pointe Noire, Congo,and Aracruz, Brazil (131). Casuarina junghuh-niana is propagated by cuttings in Thailandand India (83). Once the technique is devel-


Table 3.—Comparison Between Container and Bare-Rooted Methods of Raising Seedlings

Container system Bare-rooted system

Materials Need as many containers as seedlings. Supply of Nursery site with easily worked soil suitable for bedgood soil for potting mix cultivation

Equipment Container filling tools, soil sieving screen. Several implements for plowing, leveling, bed forma-Tubing shed tion, seed sowing, undercutting, lifting, etc.

Labor Labor intensive, not easily mechanized. Much labor Well suited to mechanization. Most labor intensiveneeded for container filling, seed sowing, weeding, components are lifting and packaging, but evenand container removal at planting. Typically 10 to these may become mechanized in the future. At20 workers per million seedlings produced Beerburrum, Queensland, 2 to 3 people raised 1.4

million seedlings per year

Transport Bulky and heavy to transport, costly over long Plants easy to transport over long distancesdistances

Silviculture Excellent survival at planting, except that overgrown Good survival depends on careful timing of liftingplants become pot-bound and suffer serious root and planting, to coincide with wet weather, anddeformation and later instability adequate conditioning of plants. Gives poorer

results where climate is unreliable

Supervision Easier to grow satisfactorily, timing of operations Requires a high degree of supervision to ensurenot too critical, but may suffer more from casual proper timing and regularity of operationsneglect of watering, shading, etc.

Protection Fresh soil in every container reduces chance of Reuse of same soil may lead to buildup of patho-buildup of pathogens or soil pests. Diseased seed- gens or soil pests. Pests and diseases more likelyIings easily isolated and discarded. Weed control to affect all seedlings in a bedtedious

cost High labor intensity tends to produce more costly P. caribaea in Queensland U.S. $20 per 1,000 (1978)seedlings. Costs per seedling including overheads E. camaldulensis in Niger U.S. $60 per 1,000 (25)are:A. cunninghamii in Queensland, using metal tubes

U.S. $70 per 1,000 (1978)Pinus caribaea in Fiji (small tubes) U.S. $30 per

1,000 (1978)E. camaldulensis in Niger U.S. $140 per 1,000 (25)Albizia falcataria in the Philippines (short nursery

life) U.S. $10 per 1,000 (1978)

Suitability All smaller nurseries and especially: 1) for good sur- 1) Large production nurseries raising only a fewvival in arid conditions, 2) when many different species for planting and where climate is depend-species are raised, 3) where plants are distributed able, 2) raising “stump” plants and as a cheapto the public and post-planting care is likely to be method for hardy speciespoor—e.g., extension nurseries

SOURCE J Evans (29)

oped, the cost of production is low. For exam-ple, at Aracruz, Brazil, 230 laborers produce10 million rooted cuttings annually at a totalcost of as little as U.S. $0.10 per plant. For mosthardwood species, a team of two to three pro-fessionals with a budget of $200,000 should beable to develop a system in 2 to 3 years (131).

Another vegetative propagation method thatholds great promise is tissue culture (also calledmicropropagation). This technique can rapid-ly produce thousands or even millions of prop-agules from a single parent; thus, it has greatpotential for genetic improvement programs.Reforestation requires planting materials withdesirable characteristics such as rapid growth,

good form, product utility, or adaptation toproblem sites (i.e., high acidity, saline soils,etc.), and the use of tissue culture can shortenthe time necessary to reproduce a large stockof planting material with the necessary charac-teristics. A large number of provenances canbe tested in a confined space within a limitedtime period for many of the particular desiredcharacteristics. (See refs. 13 and 98 for moreinformation on tissue culture.)

The technology is well established in tropicalagriculture and tropical horticulture (e. g., oilpalm), but it is still in the developmental stagefor most tree species. The cost of plantlets andthe sophistication of the technologies make

Ch, 2—Reforestation Technologies ● 2 1

Table 4.—Vegetative Propagation Techniques Used With Tree Species—

Technique Description Advantages Disadvantages

Grafting and budding The union of a shoot or branchonto the rootstock of anotherplant

Cuttings The induction of root forma-tion on sections of stems,branches, or suckers (the for-mation of sucker shoots onsections of roots from somespecies)

Propagation of elite selectionswhich do not root readily

Maturity/juvenility of the treeis preserved. Mature tissuecontinues to produce seed

Preservation of maturity orjuvenility of mother tissue.Mature plant cuttings con-tinue to flower and produceseed

Resulting plants can bescreened for resistance tosoil pests

Least labor intense means ofvegetative propagation

Many trees are graft.incompatible

Cuttings may not survive thetime period to root

Very difficult with many treespecies

May require up to 1 year forsome trees

Air layering The induction of root forma-tion on shoots that are stillattached to the mother tree

Tissue culture The sterile culture-of smallpieces of the mother tree(such as buds, leaf tissues,etc.). Also known as “micro-propagation”

SOURCE Plant Research Institute, OTA background paper, 1981 ‘-

Maturity/juvenility of plants ismaintained: shoots frommature tissue plants will con-tinue to produce seed

Shoots are nourished by themother plant

Very high volumes of plants Useful when other methodscan be produced in short are not feasibleperiods of time from a small Most labor intense methodamount of mother plant Mature tissues become juve-

nile so no seed can be pro-duced rapidly

Requires use of specialfacilities

Some potential for geneticvariation

tissue culture unlikely to replace the use of cut-tings for large-scale reforestation in tropicalareas. Its nearer term use is likely to be in es-tablishment of “super tree” orchards to pro-duce seeds or cuttings.

Mycorrhizae and Rhizobium

Seedling survival and growth rates in thenursery and at the planting site can sometimesbe improved by using special kinds of fungiand bacteria. Associations between tree rootsand mycorrhizal fungi are essential for healthygrowth of most tropical trees. The fungi are ac-tive in the transport of nutrients and water toplant roots and, in some cases, are importantfor the release of nutrient elements from min-eral and organic soil particles (76). Populationsof mycorrhizae are found naturally in soils, butthese can be depressed after long-term clear-ing and/or topsoil removal, making reestablish-ment of vegetation on degraded lands difficult.

Trials have shown that seedlings inoculatedwith fungi show improved growth and survivalover uninoculated controls (18,21,56,70,77).Some scientists suspect that certain fungi pro-vide plants with resistance to low pH, heavymetal toxicants, high temperatures, and otherstresses common to degraded sites.

Methods for reinoculating damaged soilswith mycorrhizal fungi include:

●

●

●

inoculating containerized plants or bare-root nursery stock prior to outplanting,pelletizing seed with mycorrhizal in-oculum prior to sowing, andinoculating soil at the planting site withlaboratory produced cultures.

These techniques are being developed, butcharacteristics of the most widely used tech-nique for inoculum production—pot culture—pose a major constraint to commercial applica-tion. The fungus is grown in association with


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Photo credit” Weyerhaeuser Co

Tissue cultured Ioblolly pine plantlet ready to betransferred from Weyerhaeuser Co. ’s

laboratory to the soil

roots of living plants in pots of soil or sand ina greenhouse. The soils, infected roots, orfungal spores are then harvested and used asinoculum. Unfortunately, this technique isbulky, clumsy, slow, and susceptible to con-tamination by pathogens (94).

Trees of the legume family can grow well ondegraded land with low nitrogen content be-cause their roots can be a symbiotic host forRhizobium bacteria which f ix nitrogen.Rhizobium bacteria, within tree root nodules,produce an enzyme that causes conversion ofnitrogen gas (available in the soil but unavail-able to the plant as a nutrient) to ammonia. Theammonia, a common fertilizer, is converted tocompounds such as amino acids and trans-ported throughout the tree for use in synthesiz-ing plant protein. Thus, some legume leaves,pods, and seeds are highly nutritious as foodor fodder, and the leaves are an excellent fer-tilizer and soil conditioner.

Maximum production of ammonia requiresinfection of the legume’s roots with the righttype of Rh izob ium. Most so i l s conta inRhizobium, but degraded soils probably con-tain fewer types and lesser amounts of the bac-teria. Thus, the appropriate type of Rhizobiummay not be present at the site of a reforesta-tion effort, or present in enough quantity to in-fect the tree roots. An association with an in-appropriate type of Rhizobium may occur, inwhich case little fertilizer may be produced.

An old inoculation technique is to collectroot nodules from a vigorous legume tree, grindthem up, and use the product to inoculate other


Photo credit: T. Wood

Nitrogen-fixing nodules formed on the roots of Acaciapennatula, a fast-growing tropical woody legume, by

Rhizobiurn species

trees of the same species. Because of differingresponses to various soil conditions, however,the collected nodules may not contain the ap-propriate type of Rhizobium. Development ofother techniques has greatly enhanced the like-lihood of the correct association. For example,different types of Rhizobium collected fromnodules from natural sites are isolated, cul-tured, and stored. Then various combinationsof tree provenances and soil types are testedagainst the various types of Rhizobium to findthe most productive combinations. Then, theappropriate Rhizobium for a particular refores-tation project can be reproduced in culture andsent to the nursery.

Inoculants from cultures are relatively sim-ple to use and cheap, costing only a small frac-tion of a cent per tree, The inoculant is inpowder form and can be applied as a dust or

slurry to the tree seed just before planting inthe nursery or field. An adhesive such as gumarabic can be used to ensure that inoculum ad-heres to each seed. Fertilizers such as lime,rock phosphate, and molybdenum can beadded to the seed coating to protect the seedand to feed the emerging seedling (48). The in-oculant also can be drilled into the soil withthe seed at planting. It is possible to inoculategrowing trees, but inoculation at the time ofplanting seems the most efficient method.

Inoculation of legumes with Rhizobium hasbeen practiced in agriculture in industrializednations for many years. Use of this techniquein tropical agriculture is not yet well estab-lished, but it is being promoted by several in-stitutions. Unfortunately, the application of thistechnique in forestry is not well accepted. In-oculants are living organisms that must betransported and stored carefully and used cor-rectly to retain their viability. These re-quirements can be difficult to achieve, especial-ly at remote tropical sites needing reforesta-tion. Most importantly, inoculants for tropicallegume trees commonly are not available be-cause of a lack of production.

These constraints are being overcome slow-ly. Inoculants for some tropical legume trees,such as Leucaena and Calliandra, are nowavailable commercially. Research centers, suchas Centro International de Agricultural Trop-ical in Colombia and the Nitrogen Fixation byTropical Agricultural Legumes project at theUniversity of Hawaii produce inoculants on apilot scale as a service for researchers and, oc-casionally, legume growers. While most of thebiological nitrogen fixation work at these insti-tutions is on nonwoody agricultural legumes,inoculants for legume trees are gradually beingdeveloped and efforts are under way to educatetropical forestry specialists about this technol-ogy.

The roots of some nonlegume trees also canbe infected by micro-organisms that producenitrogen fertilizer for the tree. Casuarina,planted on tropical degraded lands, is an ex-ample of this group of trees. Techniques toculture the micro-organisms that associate with


Photo cred i t Wood

Nitrogen-fixing nodules formed on the roots of red alder(Alnus rubra) by an actinomycete in the genus Frankia

these nonlegume trees are not yet available.However, the use of ground nodules from al-ready established trees is possible and practicalfor areas where these trees are native.

Soil Conditioners

Soil conditioners, used to increase soil pro-ductivity, are materials other than commercialfertilizers or organic matter that change theproperties of soil physically, chemically, orbiologically (4). Chemical substances such asAgrosoke and Erosel (plastics) or “super-slurper” (water-holding starch copolymers) areexamples. The super-slurper was developed bythe U.S. Department of Agriculture to increaseseedling survival and growth rates through anability to absorb, store, and release water to theplant on demand (5). Although it is betterknown in agriculture, it has shown promise

when applied to tree seedlings, and it may haveapplication in tropical forestry, especially inareas where rainfall is limited and sporadic,and where plant desiccation is a problem.

Super-slurper can increase aeration and im-prove drainage through its expansion capabil-ity. It can be used in a variety of ways: mixedinto soil or greenhouse media, applied as seedcoating, distributed in the hole prior to trans-planting, and broadcast over an area to beseeded. The latter, however, is prohibitively ex-pensive because of the amount required andthe biodegradable nature of the copolymer. Themost promising, economically sound use ofsuper-slurper is its application into the slurrybucket during bare-root planting. This is an ef-fective means of preventing bare root desicca-tion.

Direct Sowing

Direct sowing means that seed is planted di-rectly at the site. This technique is feasiblewhere seed is plentiful and where mortality ofseed and germinating plants is low (101). Thusfar, only a few species have been planted thisway in the tropics: Acacia arabica, A. mearn-sii, Gmelina arborea (Senegal/Gambia), Leu-caena Zeucocephala (Philippines), Azadirachtaindica (Nigeria), Cassia siamea (Tanzania), andPinus caribaea and P. oocarpa (Honduras)(65,78).

The advantage of direct sowing is that nonursery is required and planting costs are low.On the other hand, seedling survival may below (23) because of weed competition, lack oftending, poor weather, or animal damage, Ger-mination success can be increased by pretreat-ing seed with fungicide, insecticide, and birdand rodent repellents.

Direct sowing can be done either by hand ormachine (e. g., tractor or plane). Although theuse of aircraft to sow seeds largely is still un-proven in the tropics, it shows promise in ac-celerating reforestation programs through itsability to seed large and remote areas quickly.It is not, however, a replacement for otherplanting techniques. It is simply another tool


1945

1976

Photo credit U S Army and James Black, Jr for NAS

Corregidor Island at the entrance of Manila Bay, bombpocked and denuded in WWII, was air sown with

Leucaena. It has become the dominant vegetation

to be considered when reforesting remote,rugged sites not easily reached by people orland vehicles.

Aerial seeding for the tropics is at a devel-opmental stage. Only a few sites and specieshave been tested. (See table 5 for a list of possi-ble candidates for aerial seeding.) The tech-nique entails many logistical problems. Lackof aircraft and logistic, administrative, andcommunications support are major constraints.The lack of large seed quantities is another con-straint. Poor control exists over tree spacings.The seeds used are usually wild or unimprovedstrains because seeds from genetically selectedstrains are yet too scarce and expensive to use.On the other hand, the mere fact that there areno capital costs for nurseries nor for the out-planting of seedlings makes aerial seedingattractive.

Transplanting Wildlings and Stumps

Other sources of planting materials exist forreforestation. Natural forest seedlings (wild-lings) and root suckers are sometimes trans-planted, usually from moist tropical forests,with variable results. Stumps, a nursery stockthat has been subjected to drastic pruning ofboth roots and shoot, can be planted directlyinto the ground. Stump planting is especiallysuited for species that have a dominant taproot(32). Examples of species that have been plantedas stumps are Acacia cyanophylla, Azadiractaindica, Cassia siamea, Chlolophora excelsa,Cordia alliodra, Dalbergia sissoo, Gmelina ar-borea, Tectona grandis, and Pterocarpus spp.(29). During transit, stumps are normally cov-ered with wet sacks or layers of large leavesto prevent desiccation.


Table 5.—Possible Candidates for Aerial Seedings in Developing Countries

Humid tropics

Acacia auricu/liformisOther Acacia spp.Albizia falcatariaAlbizia lebbekOther Albizia spp.Anthocephalus chinensisAvicennia spp. and some

other mangrovesCalliandra calothyrsusCassia siameaOther Cassia spp.Casuarina spp.Cecropia spp.Croton spp.Derris indica (Pongamia glabra)Eucalyptus degluptaOther Eucalyptus spp.Ficus spp.Flindersia brayleyanaGliricidia sepiumGmelina arboreaLeucaena IeucocephalaMacaranga spp.Maesopsis eminiiMelaleuca spp.Melia azedarachMelochia indiciaMuntingia calaburaMusanga spp.Neoboutnoia spp.Pinus caribaeaPinus kesiyaSesbania grandifloraSpathodea campanulataSyzygium cuminiTerminalia catappaTrema spp.SOURCE Nat/onal Academy of Sc/ences (78) –

Semiarid areas

A c a c i a a l b i d aAcacia niloticaAcacia salignaAcacia senegalAnacardium occidentalAzadirachta indicaColophospermum mopaneEucalyptus citriodoraEucalyptus tereticornisHaloxylon aphyllumHaloxylon persicumPinus halepensisProsopis spp.Zizyphus mauritianaZizyphus spina-christi

Tropical highlands

Acacia mearnsiiAlnus acuminataAlnus nepalensisAlnus rubraCallitris spp.Eucalyptus globulusGrevillea robustaInga spp.Mimosa scabrellaPinus oocarpaRobinia pseudoacacia

LAND PREPARATION

Nutrient deficiency, soil compaction, lack ofwater-holding capacity, and surface hardnessare characteristics of degraded lands that influ-ence the success or failure of plant establish-ment. Because of these problems, many sitesneed some type of preplanning preparationsuch as fertilization, clearance of competingweedy vegetation, or loosening of the soil. Thedegree and type of land preparation dependon several factors: capital and labor available,site and soil conditions, vegetative cover, andspecies to be planted. For example, lmperatagrassland may require burning and disking be-fore planting Eucalyptus, a tree that requires

completely weed-free sites for rapid earlygrowth, whereas direct seeding of Calliandraon unprepared sites has been successful (29).

Manual v. Mechanical Clearing

Land preparation can be either done by handor by machine. On degraded lands with grassor weeds, the land is usually disked. Burningis an efficient method under certain conditions,On gentle slopes or flat degraded lands, the useof tractors is popular. In areas with residualscrubby trees, large tractors with heavy chainsbetween them are used to pull down undesir-

Ch. 2—Reforestation Technologies ● 2 7-—

able trees. Some of the vegetation might beused to make charcoal or be burned. Landclearing methods involving hand or chain sawcutting followed by burning may be better thanclearing by heavy equipment. The reasons are:1) ash has fertilizer value, 2) heavy machinerycan cause soil compaction, and 3) bulldozerscan displace topsoil (106). On fragile, steepslopes with highly erodible soils, the onlysuitable method is to manually cut, pile, and/orburn the scrub vegetation (135).

Further advantages of manual methods arethat they are less constrained by the rainyseason, they require few skills, and the capitalcost is relatively low. In addition, manual landpreparation provides temporary employmentto laborers and causes minimal damage to soil.A disadvantage of manual clearing is the needto recruit, manage, and provide logistics in re-mote areas for a substantial number of labor-ers, Mechanical clearing, on the other hand,requires high capital inputs for equipmentmaintenance; supplies of fuel, oil, and spareparts; and operator training and supervision.yet in general, mechanical clearance is cheap-er than manual clearance (29), The choice be-tween manual and mechanical land prepara-tion must be made on a case-by-case basis, de-termined by all these considerations.

Sell Improvement

On degraded sites, land preparation is espe-cially important for soil improvement. Plow-ing suppresses weeds and breaks up soil sur-face compaction, and ripping breaks up deep-er, hardened layers. Contour plowing or usingcontour barriers of dead vegetation also canreduce soil erosion in areas where vegetationis cleared. Both plowing and ripping are lim-ited to gentle topography. Catch dams, benchterraces, and contour trenches all function toarrest soil movement, thereby improving soilstability and productivity. Ridging in variousforms–tie ridging, stepped ridges, small catch-ments—serve to improve drainage and soilaeration and to retain water on the site (40,128).

The soils of degraded lands commonly arepoor in available nutrients; therefore, it may

be necessary to add nutrients during landpreparation. Several techniques exist to in-crease soil nutrients, including mulching withorganic or inorganic matter, the use of greenmanure (especially herbaceous legumes), theuse of nitrogen-fixing trees, and commercialfertilizers,

Mulching—placing vegetative matter aroundthe base of the tree—suppresses weeds, im-proves soil moisture conditions, and augmentssoil organic matter (95). Legume or nonlegumenitrogen-fixing trees can improve soil withtheir ability to produce nitrogen fertilizer [seesec. on “Nursery Planting Stock”). Foliagedropped by legumes is nitrogen-rich and willaugment soil fertility as it decays.

Historically, tropical foresters have reliedmore on seed provenances and thinning prac-tices than on commercial fertilizers to increaseproductivity (92). Use of commercial fertilizersfor forestry purposes is not likely to becomewidespread in the tropics given their high costand the priority given to their use in food pro-duction. In most tropical countries, much ofthe commercial fertilizer must be imported.The cost in foreign exchange combined withuncertainty of plant response limit their ap-plication. However, Carton de Colombia hasexperimented with the application of about 50grams (g) of fertilizer in planting holes on ex-tremely nutrient poor soils. The results after3 years have been promising (68). If smallamounts of fertilizer can produce significantresults, further evaluation is needed to deter-mine the best formulations and amount of nu-trients needed per seedling. Research is neededon other deficiencies that limit growing trees.

Some highly weathered tropical soils offerproblems when fertilized with essential plantnutrients such as phosphorus and potassium.Phosphorus can become so tightly held by soilminerals that plants can extract little for theirbenefit, whereas potassium is not held by thesoil and is leached away (37,64). The use of thewrong fertilizer, or incorrect amounts of fer-tilizer, can reduce yields. For instance, applica-tion of 100 g of potassium chloride (KC1) perPin us caribaea tree depressed growth and in-


creased mortality on Nigerian savanna sites(61).

Moreover, the use of fertilizer may causewater-associated environmental problems suchas increased eutrophication that hampers nav-igation (52) and may trigger the onset of newhealth problems. For instance, a large part ofthe Amazon River Basin has the required en-vironmental conditions for the presence ofschistosomiasis, a serious parasitic diseasetransmitted by freshwater snails. Chemicalanalyses of waters draining large areas here

show a dilute mineral content nearly equiva-lent to that of distilled water (107,117). Thedisease is absent probably because the waterscontain so little calcium that the snails cannotbuild shells. The introduction of lime, even insmall quantities, into such waters might pro-duce significant environmental changes, in-cluding spreading schistosomiasis. Fertilizerscan be both beneficial and detrimental, so theimpacts of various fertilizer application needto be thoroughly examined before widespreaduse.

TREE PLANTING

Reforestation of degraded lands is similar toreforestation in general. The main differencesare the intensity of site preparation, the selec-tion of tree species, and intensity of mainte-nance and protection. Well-established technol-ogies for propagating, planting, and tendingcertain tropical trees and tree crops have beenapplied in developing countries. These technol-ogies, however, need refinement and adapta-tion for local site conditions. The managementof soils, particularly where continuous tree pro-duction is the goal, is of great importance (75,104), If reforestation of degraded lands is to beprofitable and, at the same time, restorative ofland quality, more work is needed in selectinghigh-yielding, fast-growing, soil-enriching, andstress-tolerant species and provenances thatproduce products desired by the local peopleor landowners.

Substantial experience and information havebeen accumulated. Foresters from developingand developed countries alike have had experi-ence with plantations, mostly growing exoticspecies—some in the tropics, some on degradedlands, Recent references on plantation technol-ogies include Evans (29), ILO (55), FAO (32),Ghosh (40), Wattle Research Institute (124), andChampion and Seth (19).

The following section draws on previous dis-cussions to assess tree planting on specificdegraded lands: eroded watersheds, semiaridand arid lands, unproductive grasslands, andsaline/alkaline lands.

Repairing Eroding Watersheds

Deforestation of montane regions is one ofthe most acute and serious ecological problemstoday (27). Some 10 percent of the world’spopulation live in mountainous areas, whileanother 40 percent live in the adjacent low-lands. Thus, half of mankind is affected by thetree cover, or lack of it, on mountain water-sheds (72). Yet no precise estimates exist of thescale of the problem. Data from FAO and otheragencies indicate that some 87 million ha ofmontane watershed land need reforestation(131),

Maintaining or replacing tree cover on moun-tain slopes is very important for soil protection(see ch, 1). Trees intercept raindrops, slowingtheir speed and transforming them into asteady, gentle flow of water down trunks andfrom leaf tips. The roots foster infiltration ofwater into the ground to replenish ground wa-ter, Removing the protective tree canopy cangreatly alter the water regime. This results infloods after heavy downpours as high intensityraindrops compact the soil surface promotingrunoff, landslides, and erosion (93).

Efforts to establish tree cover on montaneslopes must overcome the erosion and land-sliding that may be common to those defor-ested sites. In areas where erosion is not severe,natural regeneration of vegetation can occurand restricting use of the site may be the mosteffective and least expensive method to reestab-


inaccessible locations aerial seeding may bemore appropriate and should be investigated.

Photo credit: US Forest Serv fce

A catch dam, constructed from local materials, is usedi n the gully to halt further soil erosion

lish tree cover. However, when erosion is acute,primitive dams made of rock, soil, and, if avail-able, tree stems and branches can be con-structed in gullies to halt soil movement down-slope until trees can be established. Such bar-riers S1OW water movement and trap soil. Chan-nels and walls can be constructed to divertwater flow from vulnerable areas. Water-spread-ing techniques can be used to spread runoffwater over relatively flat areas, reducing itserosive potential. Control of sheet erosiondown a slope can be accomplished by terrac-ing, contour hedges and furrows, and low re-taining walls.

Planting sites in montane environments mustbe prepared by hand to avoid soil damage.Where trees are to be established on degradedwatersheds, it is necessary to have tall, well-established seedlings by the end of the first yearto avoid being shaded by the ground coverplants, Seedlings raised in containers have bet-ter survival and initial growth rates than bare-root seedlings. They can be prepared for siteconditions (hardened) in the nursery by re-peated root pruning and by regulating water-ing and amount of direct sunlight (39]. How-ever, use of bare-root seedlings often allowslarger areas to be planted (96). In remote and

To ensure that watershed protection con-tinues, reforestation programs must integratethe people’s needs for food, fodder, and fuelwith the need for watershed protection. Spe-cies selection should be based on productiveas well as restorative characteristics. Fast-growing legume trees and other multipurposetrees can help to meet these criteria, as canagroforestry, where trees are used to supportand enhance agriculture. Project planningmust also take into account the people livingin the lower reaches of the watershed and inother nearby areas. Their demands on thewatershed for wood and other products mustbe either met or supplied from elsewhere fora reforestation program to be assured success.

Reforesting Unproductive Grasslands

Conversion of tropical rainforest into farmor grazing land commonly results in rapiddepletion of soil plant nutrients and ac-celerated soil erosion. In some places, thedegradation process leads to takeover by per-sistent, aggressive weed species of low nu-tritive value (9). Often the combined problemsof low soil fertility and weed infestationbecome so great that the land is abandoned.Such lands are subject to frequent uncontrolledfires. Whenever the vegetation is burned, ero-sion becomes very severe, and productivity isreduced further. These lands can contribute todegradation of other sites by causing increasedsiltation of waterways, floods, and periodicwater shortages.

lmperata is the main invader grass speciesin Southeast Asia and parts of Africa, Knownalso as cogon and alang-alang, this sharp-edgedgrass grows a dense network of roots and un-derground stems, crowding out other speciesand depriving them of moisture during the dryseasons, Because Imperata is an aggressive,rhizomatous grass, burning may induce rapidregeneration, Plowing Imperata rhizomes intopieces only encourages it to regenerate intoseveral plants (105].

30 • Background Paper #l: Reforestation of Degraded Lands

Imperata occupies some 16 million once-forested ha (one-twelfth of the total land area)in Indonesia (31,62,116). The Indonesian grass-lands are expanding by 150,000 ha annually(109) and could eventually cover an area com-parable to existing cropland. In the Philippines,Imperata covers one-fifth of total land area (41).It has been identified as a problem in Thailand,Malaysia (31), and Papua New Guinea (99). Ifthe percent coverage of Southeast Asia is simi-lar to that of Indonesia, there maybe 40 millionha of Imperata grasslands in the region.

In Central and South America, the invasionof toxic weeds into cattle ranches cleared fromvirgin forest is a growing problem. Soil nutrientdepletion and weed invasion can cause live-stock production to drop to such an extent thatranches have to be abandoned. Comprehensivestatistics are lacking, but estimates indicate thatsome 8 million ha of forest have been clearedfor 350 large ranches in the Brazilian AmazonBasin and an unreported area for another20,000 smaller ranches (115). Yet 85 percent ofthe ranches in one major area around Para-gominas has been abandoned (50).

Special treatment is needed for those areasinfested with Imperata and for the many aban-doned cattle ranches in the Amazon Basin andelsewhere in Latin America. Although the tech-niques discussed here were developed for landscovered by Imperata, the basic principles canbe applied to other derived grasslands.

Techniques for ReforestingImperatu Grasslands

Tree species selected for reforestation of 1m-perata grasslands should possess the followingcharacteristics to counter those factors thatallow grass to dominate:

easy establishment,rapid early growth in poor soil conditions,deep rooting,dense crown to shade out Imperata,nitrogen-fixing and soil-improving charac-teristics, andfire resistance (131).

Acacia auriculiformis, Calliandra calothyrus,Gliricidea maculata, and Leucaena leuco-cephala are species that have been used exten-sively in Southeast Asia, Acacia auricu]iformiswill grow on the poorest sites, is deep rooting,and has a dense crown (102). Direct seedingof A. auriculiformis on Imperata grasslands inMalaysia yielded poor results, but large seed-lings of this tree can withstand competitionfrom the grass (86). The use of 20 centimeter(cm) tall seedlings raised in nurseries in plastictubes gave good results (8). Best tree growthresults if the grass is cut and burned prior toplanting (129). A. auriculiformis is susceptibleto fire, but this has not been recorded as a causefor failure of reforestation projects (131). It alsois a drought-resistant, soil-improving species.

Calliandra calothyrus is a fast-growing, deep-rooted tree with a dense crown. It improvespoor soil by nitrogen fixation and high litterproduction, and it is fire resistant (102). In atrial of direct seeding of Imperata grasslandthat had been burned and plowed, the survivalrates after 7 years were:

C’. calothyrus 10.4 percentL. leucocephala 8.3 percentA. auriculiformis 2.6 percent

Success was not obtained where the site wasnot first prepared (47). Indonesians use Callian-dra to reforest land infested with Imperatacylindrica, Eupatorium species, and Sac -charum species (83).

Gliricidia maculata grows faster than C.calothyrus and can tolerate very poor soils thatwould be unsuitable for the latter species. Itimproves soil through nitrogen fixation and lit-ter production. It has the disadvantage, how-ever, of an open crown that allows somegrowth of weeds such as Imperata due topenetration of sunlight (102). G. maculata hasbeen used to control the growth of Imperatain young rubber plantations (110) and is easilyestablished from cuttings. The establishmentof L. leucocephala seems difficult by compari-son (30),

On upland grass-covered sites, Leucaena Zeu-cocephala has not grown so rapidly as the trees

Ch. 2— Reforestation Technologies •. 31—

listed above. The varieties of Leucaena avail-able for reforestation are better suited to mar-ginal lowland conditions (sea level to 500 me-ters (m)) (11). Some varieties grow rapidly tobecome trees, while others have a shrub form.Leucaena canopy is fairly open in the earlyyears after planting; thus, careful tending isnecessary to reduce competition from weeds(11). Given early attention, L. leucocepha]a canestablish itself firmly. Some of the shrub vari-eties have rapid and copious seed production,enabling the shrubs to spread down slopes andproduce dense cover. Leucaena, planted withno other vegetation, may not suffice for ero-sion control on steep slopes because the leavestend to fold up at night and when under stress,thus reducing the amount of canopy cover toshield the ground from heavy rain. It is a soilimprover with good litter production, nitrogenfixation, and very deep rooting. The latter, to-gether with very rapid resprouting after cut-ting, indicates potential resistance to grassfires. In addition, dense stands may shade outundergrowth, leaving little grass on the groundto burn, making it usefuI as a firebreak (81).

In the Philippines, planting has been donesimply by burning the grass, opening a furrowwith a plow pulled by a water buffalo, anddropping in Leucaena seeds, In about 3 years,

##\it . t - .<!

.#’-. . .

‘ -: *;?t “ x,ai,,%< H “,*, ..-“? ~•ÿÿÿø .,

Photo credit: Btsson

Planting bare-root Leucaena seedlings on Imperata-infested grassland i n the Philippines

a thicket of Leucaena exists, and the perniciousgrass is gone (81).

Arid and Semiarid Lands

Desertification can occur not only in arid andsemiarid lands but in certain humid environ-ments as well, In either case, removal of thevegetative cover alters the water regime andreduces the moisture content of the soil, lead-ing eventually to desertlike conditions, An es-timated 1.56 billion ha of tropical lands areundergoing severe desertification (I 14]. T h eproblem is particularly acute in Africa andLatin America, Reforestation of these degradedlands is intended to:

• stabilize soils, including sand dunes,• reduce wind and water erosion,• improve microclimates, and• produce fuel, fodder, and other products.

For detailed descriptions of reforestation tech-nologies appropriate for decertified land, seeKaul (63), Goor and Barney (42], Weber (127),Adams et al. (l), Delwaulle (25), and Evans (29).Since water is the main constraint in semiaridand arid lands, reforestation techniques gener-ally entail improving water conditions, whichalso include choice of tree species, water man-agement, soil stabilization, and protection oftrees.

Drought Resistant Species: Many trees andshrubs native to arid and semiarid areas aredrought resistant. These drought resistant spe-cies can be improved through genetic pro-grams designed to identify, breed, and propa-gate the most productive of the drought tol-erant provenances. Most of the drought resist-ant species can be reproduced by vegetativepropagation (131) and this can be very impor-tant for species susceptible to seed-eating in-sects such as Prosopis cineraria,

In arid and semiarid areas, nursery-grownseedlings are normally used instead of seedsbecause seeds may be sought after by smallmammals or insects. Good nursery practicesare essential, Great care is needed to producea hardened plant with a well balanced, straightroot system, Sometimes, direct sowing of

32 Ž Background Paper #l: Reforestation of Degraded Lands

drought resistant species is preferred, especial-ly for the species that have long and fast-growing taproots that may be damaged in anursery or in transfer to the field.

Other Species: In arid or semiarid regions,the major limiting plant nutrient is likely to benitrogen. Hence, the use of nitrogen-fixingtrees can be extremely valuable. Lists of numer-ous tree species adapted to these areas and thathave proven successful are found in Goor andBarney (42), Weber (127), Adams et al. (l), NAS(79), and Webb et al. (125).

Water Management: Successful reforestationin areas with low rainfall depends on collec-tion and retention of water at the planting site.Water must be directed to the rooting zone oftrees and retained there as long as possible.Methods include plowing and ripping the soilsurface to increase infiltration, ripping parallelto the slope to retain water, construction ofbench terraces on steeper slopes, and funnelingmoisture onto a smaller area (water harvesting).The latter requires construction of minicatch-ments that concentrate water into the rootingzones of individual trees. The treatment of soilwith mulches of dust, organic matter, plastic,or light-colored stones can reduce evapotran-spiration and thus conserve water. Except formulching and construction of minicatchments,most water-management techniques requirethe use of tractors and other machinery.

Soil and Sand Stabilization: The destructionof vegetation in arid and semiarid areas makessoil susceptible to wind erosion. Drifting sandencroaches on agricultural land and engulfssettlements (32). However, where the sands canbe stabilized, they can often be successfully af-forested and become productive.

The principle of dune stabilization is to im-mobilize the sand long enough for vegetationto become established. The usual practice iseither to erect artificial barriers of brushwoodor other materials in a grid pattern or to plantsand-binding grasses and trees in a similar pat-tern. Planting large nursery stock in deep pitsmay obviate the need for other dune treat-ments. The use of a mulch or a heavy liquidderived from petroleum or latex as a ground

SOURCE’ F, R Weber for VITA

Microcatchments are used in reforesting arid lands.Small depressions are constructed around the base ofseedling or small tree with the general slope of the

surrounding soil surface shaped to moverainfall towards the tree

Photo credit: U.S. Agency for Irrternational Development

Planting sand-binding grasses to stabilize shifting sand


cover has had some success, but is less reliablethan traditional methods and has only beenused on a pilot scale (90,131).

The goal of reforestation on shifting sanddunes is to establish firm rooting by the plant.Only those plants that thrive on fluctuatingmoisture and nutrient supply and germinatewith little water seem to succeed. A plantingmethod consists of mixing together seeds ofseveral species and sowing them at three dif-ferent depths in a trench—near the surface,slightly deeper, and at about 8 cm from the bot-tom. During a good rainfall season, the seed-lings on the bottom maybe killed by waterlog-ging while the top ones survive, but during alight rainfall season, the top two lines may diebecause of desiccation while the bottom onessurvive (39).

Complete Protection: The exclusion ofbrowsing animals in many regions—even inareas with shifting sand—will result in recov-ery of the natural herbaceous and woody plantcover. Sometimes natural regeneration can oc-cur despite centuries of land degradation.Since local people in arid and semiarid landsusually depend heavily on livestock, a solutionis to provide an alternative source of fodder byplanting fast-growing hedges that provide nu-tritious foliage and have the ability to resprout,The problem is often to convince the herdersto pen the cattle and cut and carry fodder fromthe hedges.

The primary causes of desertification aresimple to list, but they are linked together ina complex web that makes the effects of thewhole greater than the sum of the individualparts. Thus, the success of any reforestationprogram, particularly in the semiarid and aridlands, will depend on more than mere tech-nical development. The cooperation of localpeople is needed to ensure protection, propercare, and thus survival of the trees, To get thiscooperation, the needs of the people as theyperceive them must be paramount when de-signing the reforestation project.

Mine Spoils: A Special Case

Mine spoils occupy little total area in thetropics, but they can be an important localrehabilitation problem where land is scarce,The treatment of mine spoils is analogous tothat of decertified lands, although the presenceof toxic chemicals may provide an additionalproblem. Reforestation of such wastelands isusually difficult, but techniques are availableto prepare the sites successful for tree growth.In general, it may be necessary to:

reshape the site to minimize erosion;cover it with soil;neutralize strongly acidic sites with lime;buffer it with peat, humus, or other mate-rials to reduce toxicity;loosen the soil for better aeration; and/orfertilize the site (32).

Site condition will have great influence onthe choice of species and the likely social oreconomic results of the reforestation effort.Costs of reforesting mine spoils are usuallyhigh, but as part of a mining operation they areaffordable. One such project, Baobab Farms inKenya, has converted an entire devastatedlimestone quarry into an economically produc-tive agroforestry plantation (12),

The list of trees suitable for planting at minespoils is limited, as not many trees can toleratethe extreme soil conditions. Species that canrapidly add humus and nitrogen to the soil arehighly desirable. For example, Casuarina treeshave been used to reclaim mined spoils in Thai-land, Papua New Guinea, and the DominicanRepublic (84),

Saline/Alkaline Lands

Saline soils contain sufficient soluble salts(e.g., NaCl] to harm plant growth by prevent-ing uptake of soil moisture. Water within theplant actually moves outward to the saline soilto dilute the salt solution. Therefore, evenwhere the saline soil is wet the plant will ex-


perience drought stress. Alkaline soils may ormay not contain soluble salts (e.g., Na2C O3) .The major drawback to use of alkaline soils isthat soil minerals retain so much sodium ontheir surfaces that plant growth and soil struc-ture are adversely affected. The kind of salt alsoaffects the platy soil clay minerals. Where soilstructure is good, the platy clay minerals arearranged in random fashion. Sodium, however,tends to reduce the random orientation of clayminerals, in some cases allowing them to rear-range in parallel layers as in a deck of cards.This orientation reduces pore spaces and thussoil permeability. Tillage problems in soils hav-ing this clay mineral arrangement are common;such soils do not break up easily.

Overall, approximately 121 million ha of sa-line/alkaline desert soils exist in the tropics: 36million ha in India and Pakistan; 31 million hain Africa; and 54 million ha in South America(35). Each year approximately 500,000 morehectares of excessively irrigated lands becomesaline or alkaline as a result of inadequatedrainage or use of irrigation water that is toosalty. Capillary action draws moisture to theirrigated soil surface where it evaporates, leav-ing salts in or on the topsoil. In some cases,salts can be leached from upland soils and bed-rock, raising runoff salinity from deforestedslopes and adversely affecting agricultural soilin lowland areas of the watersheds by causingtemporary or lasting waterlogging and conse-quent salinization (10). Even the continuous ad-ditions to the soil of salt from sea breezes canhave negative effects (16). Other factors thatcontribute to formation of saline and alkalinesoils include the presence of impervious sub-soil layers, a dry climate, saucer-shaped topog-raphy, and use of brackish irrigation water (39).

Techniques for Afforesting Saline andAlkaline Lands

Reforestation of saline and alkaline lands canhave a number of beneficial effects on the phys-ical, chemical, and biological soil properties:

● soil surface shading by trees reduces sur-face evaporation and, consequently, the

upward movement of ground water anddeposition of salts in upper soil layers;the penetration of roots opens up the soil,improving permeability and facilitatingleaching of deposited salts;soil structure and microbiology are furtherimproved by incorporation of organic mat-ter deposited on the surface as litter; andincreased transpiration from vegetativecover can reduce waterlogging by lower-ing the water table in areas where it is toohigh.

Successful reforestation of salt-affected landsdepends on the following:

1.

2.

Careful analysis of soil chemistry andstructure. Soluble salt concentration andpH should be among the first measure-ments to be made. (In practice, selectionof planting material often proceeds with-out even this fundamental information, )Correct choice of planting and soil enrich-ment techniques to match soil character-istics:●

●

●

●

●

●

In many cases, trees must be planted indeep pits to get maximum survival rates.Planting on bund ridges (dikes) has beensuccessful in some cases as such micro-sites are better drained, which promotesleaching of toxic salts,Establishment of trees in alkaline soilsoften requires addition of soil amend-ments and fertilizers, such as 5 kilo-grams (kg) of gypsum per pit to replaceexchangeable soil sodium with calcium,and application of nitrogen and phos-phorus fertilizers and/or green manure.In saline soils with pH less than 8.5, itis possible to secure good tree establish-ment without replacing the soil, andeven the gypsum may not be required.Trees should be planted in alkaline soilsimmediately after the start of the rainyseason, For saline soils, planting shouldfollow two or three heavy showers thatleach out salts (22).For most tree species irrigation shoulduse freshwater only, Weeding also isnecessary in the first 3 years (22).


● Seedlings should be of a proper size formaximum survival—e,g., over 1 meter(m) for Eucalyptus hybrids, and over0.45 m for Acacia nilotica and Prosopisjuliflora.

3. Selection of species suitable for particularsite characteristics. Table 6 lists speciesthat grow well in saline and/or alkalineconditions. The table also shows some im-portant economic uses for some species.

cannot be guaranteed in such extreme con-ditions. In the State of Haryana, India,Prosopis juliflora and Acacia nilotica a r egrown together on severely deterioratedsites having sporadic tree/shrub cover. P.juliflora is grown on barren regions, andA. nilotica can produce high yields offuelwood and fodder. Proper seed selec-tion and plantation management can re-sult in trees with good form rather than

Yields and quality of produce, of course, low, spreading shrubs,

Table 6.—A Selection of Tree Species Tolerant of Saline and Alkaline Conditions+

Species

Acacia niloticaa

A. salignaA. tortilisAlbizia lebbekAzadirachta indica

Butea rnonospermaCasuarina equisetifoliaa

Dalbergia sissooEucalyptus hybrida

E. camaldulensisa

E. gomphocephalaE. microthecaE obtusaE. occidentalisE. tereticornisGleditsia triacanthosHaloxylon ammodendronLeucaena leucocephala(K8 and Fiji varieties)

Pongamia pinnataProsopis julifloraa

Prosopis pallidaProsopis tamarugoa

Tamarix aphyllaa

T. maniferaT. ramosissimaT. tetrandaTerminalia arjuna

—.—Saline tolerance

up to 0.3 ”/0 ssc “ –

Saline soils—

Saline soils (moderate soils)Sites free of salt intop 60 cm. Up to0.45% SSC subsoil

As A. indicaCoastal sites, sandy areas

A A. indicaup to 0.3 ”/0 sscEC 12 to 17 mmhos/cm in top 30 cmSaline soilsSaline soilsSaline soilsSaline soilsSaline soilsSaline soilsSaline soilsSaline soils

As A. indica0.54 ”/0 ssc (up to 1% ssc)Coastal sitesHighly saline tolerantSaline soilsSaline soilsSaline soilsSaline soilsAs A. indica

— —Alkaline tolerance

Up to pH 9Alkaline soilsAlkaline soils

—Up to pH 9.8

As A. indica—

As A. indicaUp to pH 9pH 7 to 8.2

—Alkaline soils

——————

As A. indicapH 9.5 (UP to pH 10)

——————

As A. indica

Uses

F w / f d / T a / G –

Fw/SC/SB/Fd/GFw/T/Fd/SCFw/T/Sh/Fd/SCFw/T/O/SB/Sh/SC/Ta/PC

—Fw/T/SC/Sh/PW/SB/Ta

——

Fw/T/SB/B/PWFw/T/SC/Sh/SBFw/T/SB

—Fw/T/Sh

—Fw/Fd

—Fw/Fd/SC

Fw/Fd/SCFw/Fd/BFw/Fd/SCFw/T/SC/SB

————

Country

India——

IndiaIndia

IndiaChina/

IndiaIndiaIndiaIsraelKuwaitSudanKuwait

—Sudan

——

India

IndiaIndiaHawaiiChileU.S.S.R.U.S.S.R.U.S.S.R.U.S.S.R,India

NOTE Salln!tv tolerance IS eXDreSSed elthe;-rn terms of Dercent soluble salt content (SSC) or electrolytic conductivity (EC) In un!ts of mmhos/cm The countrv hstl na

denote’s the country In which the relevant trials were made It IS not an exclus{ve listing‘Denotes species of particular Importance for reclamation of sallne/alkaline lands

Key to Economic Uses B —bee forage, Fd—fodder, Fw—fuelwood; G —gum, O—oIl, PC—pest control, PW—pulpwood, SB—shelterbelts, SC— soil conservatlon, T—timber of whatever qual!ty, and Ta—tannin

+ Mangr eves are not In c l u d e d

SOURCE Yadav (134) Goor and Barney (42) and NAS (79)


PROTECTION AND MAINTENANCE OF TREES

Reforestation does not stop after the treeshave been planted. To be successful, reforesta-tion efforts require protection of young treesfor years. Proper care and maintenance of theplanted site are essential to ensure survival oftrees to maturity. Once grown, there is theproblem of monitoring timber harvests and ofsystematic replanting, To pay workers to planttrees is not difficult, but to provide incentivesfor people to keep them alive is. Primary causesof reforestation failure, other than inappropri-ate technologies, are uncontrolled grazing andfires, competition from weeds, and uncon-trolled cutting for fuel, fodder, and lumber.

Protection From Livestock Damage

Livestock grazing is a common cause of re-forestation failure, especially in the semiaridand arid tropics. Direct protection throughfencing or guards tends to be very expensive.Other, less costly, methods include planting un-palatable trees (e.g., Cassia samea) or thornytrees (e.g., Parkinsonia) as barriers around theplantation. The use of living fences is becom-ing a more widespread practice because theyprovide a number of auxiliary benefits in-cluding shade, fodder, windbreak effect, fuel,and wildlife habitat.

Photo credit G Budowski for NAS

Diphyse robinioides used as living fence posts in CostaRica, The fence provides protection and shade foranimals. Its foliage can be continuously harvested for

forage, firewood, or green manure

Another alternative includes subsidizingfarmers with livestock feed or with cash to pur-chase feed during the period when trees aremost susceptible to animal damage. Once thetrees are firmly established, controlled accessto the planted area is allowed for controlledtree pruning for fodder. Grazing underneaththe tree canopy can be beneficial as a meansof weeding, However, livestock grazing onrecently reforested watersheds can be harm-ful because animals compact the thin topsoil,thus leading to poor tree growth and increasedrunoff, The use of game repellent, tested in theUnited States against deer, has promise. Simi-lar tests must be conducted for goats andsheep.

Weed Control

Weeding is an important aspect of plantationestablishment. Weeds compete directly withseedlings for light, soil nutrients, and water.They can smother and eventually kill youngtrees by shading and growth habits, They alsoincrease fire hazards and shelter harmfulanimals (29).

There are three main methods of weeding—manual, mechanical, and chemical, The man-ual method is the most common and straight-forward and requires little skill or capital. Itcan be done on all sites, in almost all weatherconditions, and with all species. Mechanicalweeding methods may be used in large planta-tion projects, but generally they are not con-sidered profitable in the tropics. In many tropi-cal countries, chemical weed control tech-niques have been tested and found successful,but because of safety and cost problems theyseldom become the main means of weed con-trol (2),

Local Participation

Where the shortage of firewood for cookingand heating is acute, wood theft probably willoccur, No straightforward solution exists fortheft when hunger and cold are the drivingforces. This reflects a prevailing social prob-

Ch. 2— Reforestation Technologies ● 37

lem that must be dealt with in any reforestationscheme. The problem is particularly acute inAfrica where women and children must travelfor many hours to gather wood for cooking (26).

Whatever the type and location of tree plant-ing, cooperation of local people is essential forestablishment and sustained use of newlyplanted trees (7). Tree planting programs aremost successful when local communities areinvolved and when the people perceive clearlythat success is in their self-interest. Becausemost trees do not yield much benefit for severalyears, the technical options offered must dem-onstrate explicit benefits to the people. Long-term financial benefit/cost analyses are notmeaningful to poor people, while social bene-fits are not easily understood or valued by proj-ect managers. On the other hand, people cer-tainly understand the concepts of scarcity andrisk and may respond to incentives. In localcommunities, support can be generated throughdemonstration plantings, commercial plantingsby entrepreneurs with larger land holdings,education of community leaders, extension andtraining programs working directly with farm-ers or laborers, and direct financial assistanceor provision of substitutes (131).

Village woodlots provide an alternative tocutting in larger areas reforested for other pur-poses. Subsidizing charcoal or kerosene is alsoan option until reforested areas can be har-vested on a sustainable basis for fuel. In anycase, incentives must be created to encouragepeople to care and maintain the reforested areauntil the benefits can be reaped. For example,a village woodlot project in the State of Gujarat,India, which involved planting trees on de-graded communal grazing lands, was able tomeet the need of the people by allowing grassfor fodder to be cut and carried to livestockduring the second year of tree growth. This ap-proach enabled the people to continue feedingtheir livestock and simultaneously care for andmaintain the reforested area (6). Often people

will quickly recognize that this method pro-duces much more fodder than when animalswere allowed to graze freely.

Another incentive is to guarantee provisionof inputs, credit, and technical assistance whenrequired. Where land tenure is a problem,measures could be formulated to offset the riskto participants caused by the lack of secureownership of the trees—e. g., giving title to theland, short-term licenses, or improved finan-cial incentives.

Trees that can provide locally valued prod-ucts are highly valued (54). Poor people do notperceive and rarely receive benefits from in-dustrial plantations. Apart from temporary em-ployment and some stimulation of local econ-omies, most benefits of commercial reforesta-tion programs go to the central governmentand the private companies involved, Eventhough forestry may offer a worker higher paythan agriculture, work may be temporary, andlabor frequently is not available when needed.During the critical planting and weeding sea-son, for example, many laborers wish to worktheir own lands. Again, forestry competes withagriculture. When given the choice, farmerswill usualIy opt for the latter. Therefore, an im-portant incentive to get individual landownersto plant trees is the possibility of growingenough food, fuel, and fodder to meet individ-ual requirements with some left over for sale.

If reforestation is done only to reestablishtrees on a degraded site, in the long run thesame forces that initially led to deforestationand degradation will continue. Experience hasshown that local participation in tree plantingcan have positive and long lasting effects onthe land and the people. Agroforestry, com-munity forestry, and social forestry systems arealternatives that seem to ensure the long-termsustainability of the restored land by design-ing reforestation efforts so that the people wholive on the site are principal beneficiaries.


REFORESTATION USING COMBINATIONS OF TREESWITH AGRICULTURAL CROPS

Tree planting, by itself, addresses the bio-physical processes of land degradation but notthe socioeconomic causes of degradation. In-creasing demands for basic human needs andinappropriate systems for producing them arethe root causes of most land degradation.Therefore, the most sustainable resource usesystems will be those that produce a combina-tion of food, fuel, fodder, and constructionmaterials. The use of multipurpose trees is onemethod of achieving this kind of productivity;the combination of such trees with annualcrops or animals is another, The latter methodis now widely referred to as agroforestry. It en-compasses all practices that combine forestry,agriculture, and livestock raising, The inter-planting of annual crops with trees in reforesta-tion technology systems may yield the follow-ing results:

• stabilization of shifting cultivators by pro-viding alternative activities;

• early returns from the use or sale of val-uable agricultural crops to offset the costsof removing unwanted vegetation and re-planting with desired species;

• benefits to farmers from increased soil pro-tection and reduced weeding; and

I

Photo credit G Budowski for NAS

Agroforestry: Three stratum coffee plantation. Coffee isplanted in the shade of Erythrina poeppigiana (leguminoustree) with Cordia alliodora (timber tree) towering above

● opportunity for self-sufficiency in agricul-ture and wood products for the individualsmall-plot landholder.

Agroforestry as a science is only in its infan-cy. Much more information is needed on theinteraction of trees and agricultural crops. Ac-tive studies are being conducted at ICRAF,CATIE, and the Forest Research Institute inDehra Dun, India,

Many agroforestry systems exist in whichtrees, livestock, and agricultural crops are usedin combination, theoretically in perpetuity. Fordetailed discussions of various agroforestrysystems, see FAO (34), Vergara (121), Grainger(44), de las Salas (24), King (66), Chandler andSpurgeon (20), and Wilkin (130). Discussion inthis paper is limited to just one of these agro-forestry systems called “taungya.” Its principalobjective is to plant crops with trees used forwood production. Taungya entails leasing for-est land to peasant farmers who clear the land,plant crops among the trees, and after anagreed period move on to clear new lands. Al-though this method has been criticized as away for colonialists to acquire labor, it doeshave applicability in some modern reforesta-tion schemes.

Taungya is a well-established agroforestrypractice. It can be used to achieve several ob-jectives: to prepare land for tree planting, plantagricultural crops among trees, facilitate weed-ing, and ensure that suitable soil protectionmeasures are taken. Taungya can, with smallchanges in rotation length of food and fibercrop and spacing regimes, accommodate a con-siderably increased food production and pop-ulation (73).

The full potential of agroforestry systemssuch as taungya has not yet been tapped. How-ever, the greatest promise of agroforestry is thepotential of addressing some key ecologicalproblems of the land and socioeconomic prob-lems confronting the people.

Chapter 3

PageTechnological Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Technological Opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Other Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Content.

Chapter 3

Constraints and Opportunities

TECHNOLOGICAL

Currently available technologies can be di-rectly applied to reforestation of degradedlands. For almost any type of land, someone,somewhere, has grown trees. However, impor-tant technical constraints exist that must beovercome to expedite reforestation. Some ofthese constraints are:

●

●

●

●

shortage of planting stock;inadequate attention to collecting, testing,and distributing high quality seeds andclones;lack of information and research; andlack of trained staff.

In addition, because it is economically infeasi-ble to reforest the broad expanse of degradedtropical land using conventional technologies,the technologies need to be redesigned to re-quire less organization, less infrastructure, andless capital investment, Only then can there berapid and widespread reforestation.

One major technical constraint to reforesta-tion is the shortage of planting stock. The seedsupply is generally adequate for species com-monly used in tropical industrial plantations(pines, eucalyptus, Gmelina, teak), althoughsome valuable provenances are in short sup-ply and their natural origins are threatenedwith genetic impoverishment or extinction. Onthe other hand, seeds for most of the multipur-pose and nitrogen-fixing tree species are avail-able only in small quantities and are often ofpoor quality. The seed supply problem can bealleviated through the use of vegetative prop-agation such as rooted cuttings or tissueculture, These techniques have great potentialto accelerate the process of matching prov-enances to specific site conditions and toreproduce those provenances on a massivescale. Caution is advised because these tech-niques greatly reduce the genetic base and thuscan increase the forest’s susceptibility to out-breaks of pests and disease.

CONSTRAINTS

Even though more seeds are needed, careshould be taken in their collection. No mecha-nism exists today to control the quality of treeseeds traded. Most tree seed dealers do notsupply adequate information on the origin ofthe seed and this results in the use of genetictypes that are poorly matched to site condi-tions. Planting the wrong seeds may cause areforestation project to fail. Similarly, it maybe difficult to trace the origin of those seedsthat do produce well to get more planting ma-terial. Seed certification procedures have beenestablished for agricultural seeds and to a muchlesser extent for tree seeds in Europe (89) ,Canada, and the United States. These are val-uable aids for controlling genetic history andseed quality, but they are extremely difficultto negotiate and control, particularly interna-tionally,

Another constraint on reforestation is thelack of relevant and timely information andresearch. Without accurate data, it is impossi-ble to understand how and why land becamedegraded or to plan the proper scale and ac-tion needed. Although the data base is improv-ing because of the Global Environment Moni-toring System (GEMS] sponsored by FAO andUNEP, it will require continuous refining andupdating, Information is unavailable on silvi-culture of various tropical tree species (es-pecially species with many uses), on speciesand provenances suited for specific sites, onmanagement of mixed-species plantations, andon the best follow-on maintenance and protec-tion.

Even when information on appropriate spe-cies and technologies is available, it often is notdisseminated effectively to scientists, techni-cians, and decisionmakers. This is partly be-cause of a dearth of published material andinsufficient information transfer within coun-tries. Another constraint on information flow

41


is the lack of an institution with a mandate tocoordinate reforestation research, develop-ment, and implementation on degraded trop-ical lands. Thus, foresters are often unawareof what is being done elsewhere in their owncountry, in other projects or administrative dis-tricts, or by various research agencies, Further-more, they are often unaware of previous workin their own region. Duplication, redundancy,and waste of precious time occur.

Finally, in most tropical countries there is alack of sufficient numbers of trained staff atprofessional and technical levels for directoperational forestry research or for extensionwork. The reasons are many:

• forestry ranks low in public recognition;• financial rewards are poor in comparison

with other professions, since most tropical

forestry jobs are in the government sector,which is poorly rewarded in comparisonwith the private sector;competition among ministries, betweenministries and industry, and among na-tional and international agencies, and theemphasis on post-graduate qualificationsfor promotion have led to a “brain drain”from the local government agencies.

Yet even when staff numbers and training areadequate, their efficiency can be impaired bypoor project management and poor logisticaland technical support (126). Further:

● government officials generally are unwill-ing to serve in rural areas where the needis greatest; presumably this will continueuntil the market is saturated with trainedpersonnel.

TECHNOL0GICAL OPPORTUNITIES

Opportunities exist to overcome these tech-nological constraints, including:

developing international systems for seedsource identification, collection, produc-tion, and distribution;supporting programs on tree improve-ment, propagation of Rhizobia and mycor-rhizae, mixed species plantations, andother related subjects;supporting efforts to disseminate researchinformation globally, regionally, and in-country;including research and dissemination ofinformation as components of reforesta-tion programs; andcreating incentives for developing countrypeople to enter forestry, such as changingthe reward systems in forestry institutions.

Lack of sufficient and appropriate plantingmaterials can be alleviated by developing in-ternational systems to identify seed origin, cer-tify quality, and collect seeds in commercialquantities; protect natural stands to conservegerm plasm; and establish seed orchards fromwhich seeds can be made available interna-

tionally. Support for tree improvement ac-tivities will encourage self-sufficiency in seedproduction and allow genetic improvement toserve local needs,

Genetic improvement can give gains of 10 to30 percent in yield in the first few generations(131), and generations can be as short as 2 to3 years for some tropical trees. Clonal propaga-tion has great potential, particularly whereseed is in short supply and where certain site-specific genetic characteristics are desired.Techniques for mass production of cuttingscan be developed locally by private nurseries,universities, or research institutions (includingforest departments). Additional research maybe required, particularly for fast growing trop-ical species with short rotations. Financial sup-port for techniques such as tissue culture mayprove beneficial in the long run because itsgreatest value may be in gene conservation.Given the potential to increase survivorshipand yield with inoculation of seedlings withRhizobium or mycorrhizae (as described in ch.2), additional support could be given to collect,identify, culture, test, and mass propagate pro-ductive strains of those bacteria and fungi.

Research on interactions between agricultur-al crops and trees has begun in many parts ofthe world, However, very little research isbeing conducted on mixing species of trees, Itis a practice that is seldom used and poorlyunderstood. Support could be given to initiatemore research in this area. The research shouldaim at both the biological interactions of treemixtures and at management systems to followwhen one species begins to dominate another.

Inadequate information gathering and dis-semination lead to inefficient expenditure offunds. The publication of information on localreforestation and research in internationallyavailable journals could help to prevent con-stantly “reinventing the wheel, ” Providing pub-lished literature to operational and researchpersonnel, especially at the field level, couldenhance the likelihood of the most appropriate,up-to-date, and low-cost reforestation techno-logies being applied to the degraded land. Re-sults of local research and management experi-ence can be published locally at low cost in theform of departmental technical notes and bulle-tins. Efforts should be made to ensure that staffmembers receive relevant materials, read them,and, where appropriate, use them. Distributinginformation internationally is more compli-cated and expensive. The Commonwealth For-estry Bureau (CFB) maintains al] of its forestryresearch information in Lockheed Dialog, acomputer-based information retrieval systemin California, but too few institutions in tropi-cal countries have access to necessary comput-er terminals or money to use this service. Mailservice and reprints are also expensive, Donorinstitutions might help by financing an inter-national information service to provide micro-fiches containing each month’s CFB abstractsto developing countries, Thus, field staff couldbe kept up to date on current literature and thelatest advances in reforestation,

Ch. 3— Constraints and Opportunities ● 4 3

Improvements in information disseminationcan be linked to a well-coordinated researcheffort based on some systematic, scientific ap-proach eliminating unnecessary duplicationand waste. In some cases assistance may beneeded from established research institutionsto design research programs and to help trainresearch staff to interpret and implement re-sults. Donor institutions can help, for example,by providing appropriate equipment, Twinningof research institutions in developed and devel-oping nations is one vehicle to provide thiskind of support. (See ref. 132 for more informa-tion. ) However, other methods to coordinatefunding for research need to be formulated.

Providing additional staff, like reforesting ad-ditional hectares, requires increased govern-ment expenditures, and, where necessary, fi-nancial or technical support from donor insti-tutions. Staff recruitment and maintenance de-pend on a rewarding career structure with suf-ficient financial inducement. In many coun-tries provision of additional staff could be pro-vided at little extra cost by restructuring forestagencies to reduce unnecessary duplicationand complex hierarchies (131).

Forestry extension is becoming increasing}important as planners recognize that projectsuccess depends largely on active participationof local people. Incentives must be developedto entice more foresters to live and work in thefield to provide necessary support to local peo-ple. Unfortunately, most existing forest serv-ices are not structured to provide forestry ex-tension services, nor is staff trained in exten-sion and communication skills (6]. Therefore,major changes are in order for forestry ad-ministration, staffing, and training—changesalso designed to acknowledge that forestry ex-tension needs to work with local women who,in many countries, perform the tasks of plant-ing and caring for crops including trees (53).

OTHER CONSIDERATIONS

Forestry is low in priority in many tropical economic returns are often spread over a longcountries, Forest plantations have not com- time and short-term profits are low comparedpeted well against other land uses because the to those of alternative investments. This is


often in conflict with government priorities forprojects with quick returns (for which leadersreceive more political credit) and with bankerswho use conventional discounting methodsand have little interest in moderate returns in30 years. In addition, the lack of comprehen-sive forestry or land use policies has preventedforestry investment and development. But firmpolicy guidelines from the governments canproduce significant results. For example, fiscaltax incentives for private reforestation estab-lished by the Brazilian Government have ledto an increase in the rate of reforestation inBrazil (103). By giving tax breaks to landownerswho reforest their lands, the Brazilian Govern-ment has given recognition to the importanceof reforestation.

Reforestation projects may not receive ade-quate funding and support because benefit/costanalysis can show unfavorable results when itfails to include both direct and indirect costsand benefits. Adequate analysis also requirescomprehensive data on costs, benefits, andman- or machine-times and productivities, yetmuch of this information is unknown at theproject planning stage. Price estimates oftenare unreliable and do not account for inflation.Information on labor requirements is usuallymissing as well, Moreover, in forestry, yieldsare difficult to predict because of the long-termnature of the enterprise, climate and manage-ment uncertainty, and, more importantly, alack of accurate information on site/species in-teractions. New technologies, such as tissueculture to accelerate vegetative propagationand bacterial inoculation to increase seedlingsurvival, are reducing the costs of reforesting

degraded lands. Yet methods are not developedto measure the important but indirect benefitsto justify investment in reforestation.

Many nonmarket costs and benefits must beincluded in economic analysis, especially forreforestation projects where the indirectbenefits may be more significant than directbenefits. But benefits such as improved en-vironmental quality are often the most difficultvariables to quantify. Economists are grapplingwith this problem. International developmentbanks tend to treat many nonmarket considera-tions in a qualitative fashion rather than try-ing to develop artificial values for them (45).However, unless treated carefully, simply list-ing nonquantified variables may serve to re-move them from consideration. Therefore,given the large uncertainties in selecting thebest method for reforestation of a degradedsite, it may be advisable to try out in practiceseveral approaches until the uncertainties havebeen sufficiently reduced (51).

Most experts find that major constraints toreforestation of degraded tropical lands areeconomic, institutional, and social rather thantechnical, A technical package, once acceptedby funding institutions and the host-countrygovernment, may solve certain problems, butmany obstacles to its acceptance remain. Ex-perts must remember that “forestry is not, inessence, about trees. It is about people. It isonly about trees so far as they serve the needsof the people” (46), Successful reforestation re-quires sufficient funds, strong political will,massive popular support, and cooperationamong all involved parties.

Appendixes

Appendix A

Commissioned Papers and Authors

Technologies and Technology Systems for Refor- Afforestation and Management of Tropicalestation of Degraded Tropical Lands Wastelands in India

P. J. Wood, J. Burley, and A. Grainger R. C. GhoshCommonwealth Forestry Institute, Calcutta, India

oxford, England

Technologies for Reforestation of DegradedLands in the Tropics

C. M. Gallegos, C. B. Davey, R. L. Kellison,P. A. Sanchez, and B. J. Zobel

Universities for International Forestry(UNIFOR)

Syracuse, New York

47

Appendix B

Acronyms

AID

CATIE

CEQCFICIAT

FAO

GEMS

GTZ

— Agency for InternationalDevelopment

— Centro Agronomico Tropical deInvestigacion y Ensenanza

— Council on Environmental Quality— Commonwealth Forestry Institute— Centro International de

Agricultural Tropical— Food and Agriculture Organization

of the United Nations— Global Environment Monitoring

System— German Agency for Technical

Cooperation (Deutsche Gesellschaftfuer Technische Zusammenarbeit)

I C R A F – International Council for Researchin Agroforestry

IDRC – International DevelopmentResearch Center

ILO – International Labor OrganizationNAS – National Academy of SciencesNFTA – Nitrogen Fixing Tree AssociationNifTAL — Nitrogen Fixation by Tropical

Agricultural Legumes ProjectNRC – National Research CouncilP I C O P – Paper Industry Corporation of the

PhilippinesUNEP — U.N. Environment ProgramUNESCO — U.N. Educational, Scientific, and

Cultural Organization

48

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>’? I , . . ‘ ,,’ ] ] ?/] I j ]J 1