New Forests17: 25–36, 1999.© 1999Kluwer Academic Publishers. Printed in the Netherlands.

Planted forests of the wet and dry tropics: theirvariety, nature, and significance

JULIAN EVANSTropical Forestry, Imperial College, London, UK

Key words: sustainability, plantation forestry, rural development forestry, environmentalforestry, silviculture

Abstract. Planting trees in tropical countries is an increasingly important forestry activity.Although much attention has been paid, and rightly so, to rapid deforestation in the tropics, thecontribution and role that planted forests can play are now at the center of policy and planningin most national forestry strategies. The changing emphasis from exploitative management ofnatural forests to managed natural forests and plantation forests, seen in temperate regionsover the last 100 years, has been taking place in tropical countries largely over the last 20years. In neither temperate nor tropical regions has this evolution finished.

Planted forests will increasingly furnish wood resources that meet domestic wood needsand provide many environmental services. In this paper I seek to place in perspective thecontribution that planted forests will make in the tropics. I emphasize (1) the wide variety ofpurposes that planted forests serve; (2) the sustainability of plantation silviculture; and (3) theoverriding importance of due regard to people’s participation. I am optimistic about the greatvalue that planted forests, rightly used, can provide for a great many hard-pressed peoplesacross the tropics and beyond.

Extent and definition of planted forests

Although it is the act of planting a tree that defines the subject, the spectrumof types of planted forests is broad, and ranges from industrial monoculturesto enrichment planting of natural woodland formations or growing fruit treesin an African compound. I confine remarks here to locations where plantinghas led to the establishment of at least a small group of trees that wouldnot otherwise be there. Sawyer (1993), in her analysis of the environmentalconcerns of plantations in the tropics, has a helpful chapter on this questionof definitions.

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Figure 1. Areas covered by tree plantations in the tropics and hotter subtropics.

Area of planted forests

Data assembled for my own book (Evans 1992) and by the Food and Agri-culture Organization of the United Nations (FAO 1993) indicate that thereare between 40 and 50 million ha of forest plantations of one kind or anotherin the tropics and warmer subtropics. Figure 1 summarizes data by conti-nent and shows the large increase since 1965. Such area data are based onreports and country returns collated from many different sources; thus, theyshould be treated critically. The overall magnitude of planting is correct andthe evidence of increased planting is correct. However, individual figures,particularly figures published by countries, are notoriously variable becauseof different reporting systems, different methods of data collection, and theall-too-frequent practice of claiming land planted based on seedlings raisedin the nursery rather than on surveys of successful tree planting.

This last problem bedevils many tropical forestry statistics, particularlythose regarding the success of extension programs where optimistic reportssimply do not match reality. Far too great an emphasis is placed on numbersand counting, far too little on follow-up and assessing what has really beenachieved. Although I know of no survey to prove the point, my guess wouldbe that no more than one seedling out of every three, carefully raised andnurtured in a nursery, survives 1 year in village and extension forestryprograms, and, at best, no more than two seedlings out of three in managedindustrial or commercial forestry programs.

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Despite the caveats above, a lot more tree planting is taking place in thetropics than in the past. A figure of around 2 million ha/yr, compared withonly 1 million ha/yr a decade ago, is a realistic estimate.

Geography of plantations

At this point it is helpful to remark on two dichotomies. One is in the titleof this paper, the distinction between the wet and the dry tropics, which cancrudely be delineated as above or below about 800 mm of rainfall per year; theother is the distinction between highland and lowland, which reflects temper-ature differences. In summary, planted forests are most successful in the cool,moist, highland tropics and subtropics; they are, perhaps, most needed in partsof the dry tropics.

Variety of tree planting

Planted forests may be classified in a number of ways, such as by theirspecies’ composition, by their scale, by their complexity, or by the purpose forwhich they are established. Different classifications serve different purposes,but the last of these is the most helpful distinction to emphasize the contrastwith temperate plantations. Planting trees in tropical countries is undertakenfor three principal reasons: industrial plantations, rural development, andenvironmental benefit.

Industrial plantation forestry

Industrial plantations have been successful, particularly in the cooler highlandtropics and on former savanna, grassland, and similar land types. Almostall such planting has been for industrial wood purposes, such as low-gradelumber, pulpwood, and some panel products. Cultivation of quality hardwoodtimbers, with the exception of teak (Tectona grandisL. f.), has proven to bemore intractable, and this is elaborated on later.

Rural development forestry

Almost all tropical countries actively promote tree planting as part of ruraldevelopment. This arises from the important role that trees play in meetingseveral crucial domestic needs, such as those for fuelwood, fodder, sticksand poles for building materials and fences, and a range of other productsused at the village level as part of everyday life. This dependence on treesfor day-to-day needs highlights a key difference between tropical and many

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temperate countries. Additionally, such trees in rural development provideshade, shelter, and a means of soil improvement through such processes asnitrogen fixation.

Rural development forestry embraces the terms “social forestry” and“community forestry,” which have fallen somewhat into disfavor because ofthe politics that have surrounded such programs, e.g., in India, Thailand, andKenya. For many tropical countries today, the bulk of tree planting activity isfor these purposes.

One important strategy in rural development forestry is planting trees inassociation with food crops, or as a source of food or fodder themselves.Although the term used for these plantings, “agroforestry,” is relatively new,the practices are frequently ancient and much profitable research is focusedon investigating the success and science of these long-practiced husbandries.

Environmental planting

A particular feature of many tropical plantations is their use to provide aspecific environmental service or to harness trees with the principal aim ofa non-timber benefit. Tree planting to assist soil erosion control, whether insupport of bunds on steep hillsides or as part of shelterbelts to reduce winderosion, is widely practised. Reclamation of wasteland and degraded areasand the less interventionist rehabilitation (according to the classification ofLamb 1994) are far more widespread in the tropics than, for example, in myown country of Great Britain.

Parallel to this are three further purposes for which the main objective isto bring about environmental benefit: (1) as carbon offsets, though obviouslyforest products may be obtained; (2) as compensatory plantations to divertpressure away from natural forest systems (again forest products are avail-able, but these plantations provide a means of saving forests elsewhere); and(3) as buffer zones around areas of natural forest, i.e., a specific locationalexample of compensatory plantations.

In several instances, more than one of these purposes is well served byplanted forests. The distinctions are drawn because the three broad rolesplanted forests can play are much more explicit in many tropical countries.All of the benefits that trees and woodlands can provide are much morecarefully thought through and used.

Plantation silviculture

The principles that underpin successful plantation forestry in temperate coun-tries apply equally to the tropics. Planted forests in the tropics, indeed

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any type of tree planting, do not differ materially in their technologicalrequirements from those in temperate regions. Plantation forestry require-ments involve six key features: species, planting stock, stocking levels,establishment, protection, and thinning and pruning.

Species choice

For both industrial plantations and tree planting in rural development, exoticspecies predominate. Indeed, eucalypts (Eucalyptusspp.) and pines (Pinusspp.) alone account for well over half of all planting that has taken placein the tropics; pines are used predominantly for industrial purposes, euca-lypts for both industrial purposes, e.g., pulpwood and pit props, and villageuse in supplying sticks, poles, and firewood. Legume species, particularly ofthe generaAcaciaandProsopis, are important in social and village forestry.Some individual species have also found a widespread niche, e.g.,Grevillearobusta A. Cunn. (silky oak) as a pole and timber tree in hedgerows andfield boundaries;Leucaena leucocephala(Lam.) de Wit (Ipil ipil) as a fodderand fuelwood species;Casuarina equisetifoliaL. (she-oak) in soil erosioncontrol and as a nitrogen-fixing species, andAzadiracta indicaA. Juss.(neem) for shade, fuel, and wood. The predominant genera and species froma compilation made in 1980 remain the important ones today (see Table 1).

There are relatively few plantations of high quality tropical hardwoods fora variety of reasons, notably because of such problems asHypsipylashootborer damage to theMeliacaea– mahoganies, khayas, and tropical cedars,and problems resulting from inadequate understanding of the ecology ofmany tropical hardwoods found in rain forest ecosystems. The review byAppanah and Weinland (1993) of experience in peninsula Malaysia wellillustrates the difficulties. The major exception is teak, which has beensuccessfully planted in many tropical countries and occupies more than 2million ha. There is no doubt that improved understanding of how to growquality hardwoods will be one way of helping to alleviate pressures resultingin tropical deforestation.

As in temperate plantation silviculture, the matching of species with siteis crucial. Successful use of planted forests in the tropics has depended onselecting the appropriate provenance for a site, developing land races, anddeveloping some astonishingly successful tree breeding strategies. Amongtropical pines, eucalypts, and, for example, the phyllode acacias, remark-able improvements have been made as a result of attention to genetics. Thisremains a priority.

Complementary to selection of genetic material is the proper character-ization of sites to match species’ requirements. Many examples exist, suchas the successful Australian Centre for International Agricultural Research

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Table 1. Tree genera and speciesa used in tropical forestry plantations in 1980 (Source: Evans1992).

Genus/group Speciesb Relative use (%)

Pinus P. patula, P. caribaea, P. elliottii, 33.7P. merkusii, P. kesiya, P. oocarpa,and others

Araucaria, Cupressus, and other A. cunninghamii, A. angustifolia, 3.0conifers C. lusitanica, and others

Eucalyptus E. grandis, E. camaldulensis, E. globulus,c 37.5E. saligna, E. tereticornis, E. robusta,E. citriodora, E. urophylla, E. deglupta,and others

Tectona T. grandis 14.2

Acacia, Leucaena, Gmelina, Grevillea, 11.6Albizzia, Meliacaea, Terminalia,Prosopis, Casuarina, Cordia,Triplochiton, and other hardwoods

a This analysis does not include data from southern China, where the main planted speciesare Cunninghamia lanceolata, Eucalyptus exserta, E. citriodora, Pinus massoniana,andP. yunnanensis.

b Order indicates relative importance.c Only successful at high elevations such as in Colombia, Ecuador, Ethiopia, India, and Peru.

programs of Plantgro and Bioclim, which have refined considerably ourunderstanding of where Australian species will grow well (Booth et al. 1989).There have also been major species’ failures. For example, trials of southernpines in the humid tropics failed from being off-site climatically, and radiatapine (Pinus radiataD. Don) andLeucaena leucocephalahave become morerestricted as a result ofDothistromasp. infection and psyllid defoliation,respectively.

Planting stock

Planted forests in the tropics are almost wholly established with seedlings thathave been grown in containers in nurseries. Very little forest establishment ineither wet or dry tropics is achieved through direct sowing or aerial seedingtechniques. All of the container systems familiar to temperate foresters areavailable and used in the tropics, but the black polyethylene bag or tube, orlocal variants such as those made from banana leaves, veneer curls, and oldtin cans, are the stock-in-trade for extension nurseries.

One other nursery practice, the use of hardwood cuttings, has proven to beparticularly successful in the tropics. Teak is the most widely used example

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of a hardwood cutting that can be kept for many weeks in a shady place andthen successfully inserted into the ground to root and grow. Indeed fenceposts of teak will often root and develop into trees! Such “pole size” cuttingsare promoted in parts of India as a quick means of tree planting, but moregenerally the use of small hardwood cuttings can be a cheap and easy-to-apply technology for villagers and farmers. The high technology equivalent ofmicropropagation and related tools is used in a number of major commercialplantations.

Tropical tree nurseries vary enormously in size from large productionunits, covering several hectares and producing several million plants eachyear, to home or compound nurseries, where the owners grow just a handfulof trees. In Britain we buy our gardening materials, trees, shrubs, and plantsfrom garden centers; in the tropics villagers bring seed and cutting materialto their homes and cultivate them there.

Stocking

Compared to temperate plantations, there is often a wider range of plantingdensity in the tropics, and this reflects the wider range of purpose for whichthe trees are being grown. In many compounds and near villages throughoutthe tropics, trees will be planted at spacings closer than 1 m or stockings ofmore than 10,000/ha. These high densities are used to grow sticks for buildinghuts and fencing materials, and also to provide easily handled firewood. Mostindustrial plantations are established at around 2.5–3.0 m spacing, i.e., about1,000–2,000 trees/ha. In agroforestry and enrichment planting silvicultures,much wider spacings are used. In both situations rows of trees may be 10 m ormore apart, and sometimes trees in each row will be equally widely separated.In the tropics, therefore, tree planting densities can vary from a few tens tomany thousands/ha, this depending entirely on the purpose for which treesare being planted.

Establishment

The nature of the site being planted largely determines the requirements forsite preparation and planting practices. This is not the place to cover such abroad subject, but the following two points are important:1. On moist, lowland, equatorial sites, vegetation growth, including lianas,

can overwhelm even the most vigorous of plantation species. This mustbe addressed in the planning stage. (As an aside, clearing forest simplyto provide land for tree planting is deprecated. It is neither necessarynor desirable when so much abandoned land suitable for planting alreadyexists.)

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2. Much tree planting in the tropics serves for both wood production and theprovision of environmental services, especially control of soil erosion.Care must be exercised that site preparation and planting activities do notthemselves worsen the very erosion problem that the project is seeking toovercome. Sometimes minimum cultivation and weed control, along withconcomitant slower establishment of the planted tree, will be preferableto applying traditional silvicultural practices.

Protection

The problems that confront planted trees in tropical countries do not differmaterially from those elsewhere. Young trees are at great risk of damagefrom browsing, trampling, uprooting, and an array of insect pests and fungaldiseases. Without due regard to these threats, all the careful work of matchingspecies with site and of preparing the site well will be wasted. Again I wouldhighlight just two issues of special relevance to the tropics, as follows:1. Villagers’ livestock and the common practice of grazing extensively

through the bush and taking animals to water represent an enormousthreat to tree plantations, particularly those that are part of community orsocial forestry initiatives. Cattle, camels, sheep, and goats can all easilywander into plantations and do immense harm – though, of course, splen-didly nourishing the beast itself! Prevention of such damage may dependon fencing, but more usually involves the use of guards or shepherdswhose duty it is to keep out such livestock. In the Bilate project inEthiopia the local villagers employed 55 shepherds to guard a 30-kmstrip of woodland they had helped to establish (Evans 1992).

2. Two insect pests are serious threats at the time of establishment. Through-out much of the tropics, but especially in Africa, termites can cause upto 100 per cent mortality in a new plantation. There are no easy cures,though wise choice of species, such as avoidance of certain eucalypts, canhelp. Leaf-cutting ants (Attaspp.) are important pests in tropical America,especially in more humid areas.

Management of stands

Compared to temperate plantations one sees conflicting trends in standmanagement in the tropics. On the one hand, the lower labor costs makeoperations such as thinning and high pruning in industrial plantations moreattractive. Many fine stands producing high-quality sawlogs and even veneertimber are being grown in tropical and subtropical plantations. On the otherhand, where trees are planted to meet domestic needs within the home orvillage, informal management of cutting the trees when their size is right

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leads to a “people’s selection system”! The woodland is a bank of materialcut and used as if it were a natural stand.

One other practice, i.e., pollarding, is widespread, but rarely receives suffi-cient attention. This is the decapitation of trees 3 or 4 m above ground, and theharvesting of branch material that sprouts from just below the cut surface. Allacross the tropics pollarding is used as a means of obtaining fodder, sticks,and firewood from trees in a way that does not kill the tree and that ensuresthat the regrowth is sufficiently elevated to be above browse height, especiallyfrom such livestock as cattle and sheep. Where there are camels and goats,the height has to be 5 m or more.

Where tree planting is used for enrichment of natural woodland, greatattention must be paid during the first few years to ensure that the plantedtree is not swamped, and expensive cleaning operations are essential for thiskind of silviculture. The principles of Dawkins (1958) still apply.

Social and economic roles

In the tropics there are some remarkably successful and remarkablyunsuccessful plantation projects. This applies to both industrial plantationsand tree plantings for rural development. Three issues, more than any other,have led to failures; these are as follows

1. Inadequate attention to questions of land tenure, tree ownership, and theculture of property in the country concerned. If this is not clarified at theoutset, untold problems can arise over people’s rights and dues. This canthreaten the success of a project, both small and large.

2. People’s participation. This expression may be cliché, but it is no lessimportant for that. All successful plantation projects depend, to a greater orlesser extent, on the willing cooperation and interest of local people, whetherdirectly or through their locally elected representatives. In forestry projectsfor rural development, involvement of local villagers, from the idea stagethrough identifying the land and its boundaries to the subsequent establish-ment and management of the woodland, is crucial. Many projects failed inthe 1970s and 1980s through patronizing attitudes of “give ’em eucalypts”without ever asking whether or not they were wanted.

3. Planning, budgeting, and market evaluation. Because plantations are inthe tropics and their encouragement is used to serve aid and developmentobjectives of developing countries, proper planning, budgeting, and marketevaluation must not be allowed to take backstage. This applies particularlyto large-scale plantation development, which has sometimes been pursuedmore for prestige and political reasons than for market economics. In several

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places in the tropics, plantations have been created and well established onlyto be abandoned within a few years because the market did not materialize,or because prices changed.

The parallel on a local scale is seen in the choice between plantingtrees and better management of existing natural woodland. The first reac-tion, usually by outsiders, to wood shortage is to suggest more planting,whereas often more careful management, such as controlled use of wood-land or modifying the cycle of coppicing or pollarding, will be much morebeneficial. Even the introduction of fuel-efficient, wood-burning stoves orsimilar improvements may be a better intervention than the expensive andlong-delayed solution of planting trees.

Plantation forestry in the tropics, in all its forms, has much to offer. Failure toaddress the preceding three issues will override all considerations of specieschoice, silviculture, and management.

Sustainability

In almost every case, tree planting in the tropics represents a more intensiveland use than that practised previously. High rates of growth and short rota-tions suggest the possibility that sites will be overstressed, which leads todiminishing fertility and poorer yields. Practices such as high stocking andcoppicing may add to this risk. Few studies have been carried out to look atsustainability of such plantation practices (Evans 1990), but what evidencedoes exist suggests that the problem may not be as serious as it might appear.In Swaziland three rotations ofPinus patulaSchlect. & Cham. have beengrown on the same site, with each rotation appearing more productive thanits predecessor, with only limited genetic improvement and without addingfertilizer (Evans 1994). Elsewhere in the tropics and subtropics, examples ofyield decline often reflect weed mismanagement or mismatching of speciesto site, rather than an inherent shortcoming of plantation forestry practices.Even the most intensively worked tree plantations generally fall short in thedemands for soil nutrients compared to food crops such as maize and yams.

In the narrow sense the outlook for sustainability appears reasonably opti-mistic. In the broad sense the question of sustainability is more open. Thereis an expectation that reliance on natural forest formations to provide goodsand services will switch to greater dependence on plantations. As attentionis switched from the complex and diverse to the simple and more uniform,there will, inevitably, be a reduction in the variety of products obtained (seeKanowski’s 1995 analysis). This, in itself, may threaten the existence and

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livelihoods of some of the tribal peoples inhabiting the remoter parts oftropical countries.

Using plantations for conservation and rehabilitation

Tree planting is seen as increasingly important for protecting natural ecosys-tems through developing buffer zones, diverting pressure away from thenatural resource, acting as a barrier around islands of refugia, and so on.Thus, planting trees becomes a tool to modify people’s use of the naturalecosystem to be conserved. Harnessing such practices as agroforestry, makingsmall-scale plantings in the home compound or village, and planting treesbeside roads, along canals, and around fields all help to fulfill this role. Thecontrast with temperate forestry is that these policies seek to change wherepeople go for their forest products, rather than, as in temperate forestry, to useplantations as more efficient means of providing them.

Similar to this role of diverting attention away from natural forests,plantations can be used to begin the process of reclamation and rehabilita-tion. Planting with useful species to enrich poor quality woodland has beenmentioned already, but there is now much interest in using tree plantations toreclaim degraded grasslands, industrial waste sites, and other ground unfitfor agriculture. Such plantings can be astonishingly successful. As a by-product they are often much more rich in carbon than was the land before,and therefore are a net carbon sink while they are growing.

Some conclusions

Planted forests in the wet and dry tropics are set to increase. In the next twoor three decades they may well begin to supersede natural forests as the mainsources of forest products in most tropical countries. Successful developmentof tree plantations fundamentally depends on people’s participation. If localpeople are committed, the planted forest will succeed. Technical requirementsfor success in the tropics are as firmly based on sound silviculture as they arefor temperate plantation forestry. Planted forests are a sustainable and flexibletool for development in the tropics. They are not a replacement for naturalforest formations, but a complement to them.

References

Appanah, S. and Weinland, G. 1993. Planting Quality Timber Trees in Peninsular Malaysia.Institute of Malaysia, Kuala Lumpur. Malayan Forest Record No. 38.

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Booth, T.H., Stein, J.A., Hutchinson, M.F. and Nix, H.A. 1989. Mapping regions climaticallysuitable for a particular species: An example using Africa. For. Ecol. Manage. 28: 19–31.

Dawkins, H.C. 1958. The Management of Natural Tropical High Forest with Special Refer-ence to Uganda. Commonwealth Forestry Institute, Oxford. Commonwealth ForestryInstitute Paper No. 34.

Evans, J. 1990. Long-term productivity of forest plantations – status in 1990. Proceedings ofthe Nineteenth World International Union of Forest Research Organisations Congress 1:165–180.

Evans, J. 1992. Plantation Forestry in the Tropics (second edition). Oxford University Press,Oxford.

Evans, J. 1994. Long-term experimentation in forestry and site change, pp. 83–94. In: Leigh,R.A. and Johnson, A.E. (Eds) Long-Term Experiments in Agricultural and EcologicalSciences. CAB International, Wallingford, United Kingdom.

FAO (Food and Agriculture Organization of the United Nations).1993. Forest ResourcesAssessment 1990: Tropical Countries. FAO, Rome. FAO Forestry Paper No. 112.

Kanowski, P. 1995. The complex future of plantation forestry, pp. 483–87. In: Potts, B.M.,Borralho, N.M.G., Reid, J.B., Cromer, R.N., Tibbitts, W.N. and Raymond, C.A. (Eds)Eucalypt Plantations: Improving Fibre Yield and Quality. Proceedings of the CooperativeCentre for Temperate Hardwood Forestry-International Union of Forestry Research Orga-nizations Conference. The Cooperative Centre for Temperate Hardwood Forestry, Hobart,Tasmania, Australia.

Lamb, D. 1994. Reforestation of degraded tropical forest lands in the Asia-Pacific region. J.Trop. For. Sci. 7: 1–7.

Sawyer, J. 1993. Plantations in the Tropics: Environmental Concerns. International Union forConservation of Nature, Gland, Switzerland and Cambridge, United Kingdom.

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