Planted Forests and Biodiversity

Planted Forests and BiodiversityJean-Michel Carnus, John Parrotta, Eckehard Brockerhoff,Michel Arbez, Herve Jactel, Antoine Kremer, David Lamb,Kevin O’Hara, and Bradley Walters

Expansion of planted forests and intensification of their management has raised concerns among forestmanagers and the public over the implications of these trends for sustainable production andconservation of forest biological diversity. We review the current state of knowledge on the impacts ofplantation forestry on genetic and species diversity at different spatial scales and discuss the economicand ecological implications of biodiversity management within plantation stands and landscapes.Managing plantations to produce goods such as timber while also enhancing ecological services such asbiodiversity involves tradeoffs, which can be made only with a clear understanding of the ecologicalcontext of plantations in the broader landscape and agreement among stakeholders on the desiredbalance of goods and ecological services from plantations.

Keywords: biological diversity, conservation biology, planted forests, stand management, landscapemanagement

P lantation forests or planted forestsare cultivated forest ecosystems es-tablished by planting or seeding or

both in the process of afforestation and re-forestation (Helms 1998), primarily forwood biomass production but also for soiland water conservation or wind protection.Although the total area of plantation forest(187 million ha) currently represents only5% of the global forest cover (Food and Ag-riculture Organization [FAO] 2001), theirimportance is rapidly increasing as countriesmove to establish sustainable sources ofwood fiber to meet the increasing demandfor wood pulp and energy. This is particu-larly the case in Asia, where an estimated62% of the global plantation forest estate islocated. Industrial plantations (supplyingindustrial wood and fiber) account for 48%of the global plantation estate. These typi-cally consist of intensively managed, even-aged, and regularly spaced stands of a singletree species (indigenous or exotic), often ge-netically improved, and are characterized byrelatively short rotations when comparedwith naturally regenerated stands (i.e., “nat-ural forests” in FAO terminology). Nonin-

dustrial plantations, established for fuel-wood, soil and water conservation (e.g.,watershed rehabilitation), and wind protec-tion, account for 26% of the world’s planta-tion forests, and an additional 26% of plan-tation forests are established for other,unspecified, purposes (FAO 2001).

During the 1990s, while natural (i.e.,naturally regenerated) forest and total forestareas continued to decline at the global level,forest plantation areas increased in bothtropical (�20 million ha) and nontropical(�12 million ha) regions. In both tropicaland nontropical regions, the conversion ofnatural forests and reforestation of nonforestareas have contributed in roughly similarproportions to these increases in forest plan-tation areas during this period (FAO 2001).It is worth noting that between 1990 and2000, the rate of conversion of natural toplantation forests in tropical regions wasabout equal to the increase in natural forests,resulting from natural regeneration of non-forest areas, and only 7% of the area of nat-ural forest converted to nonforestland uses.In nontropical areas the net increase in nat-ural forest areas was more than three times

the rate of conversion of natural to planta-tion forests.

About 60% of plantation forests are lo-cated in four countries (China, India, Rus-sian Federation, and the United States). Spe-cies in the genera Pinus and Eucalyptus arethe most commonly used in plantations(30%), although the overall diversity ofplanted tree species is increasing (FAO2001). Table 1 provides a summary of plan-tation forest areas and their geographic dis-tribution.

What Is Biodiversity?Biological diversity is defined as “the

variability among living organisms from allsources including . . . diversity within spe-cies, between species and of ecosystems”(Convention on Biological Diversity, UnitedNations 1992). Forest ecosystems shelter amajor part of terrestrial biological diversity,including an estimated 80% of all terrestrialspecies; approximately 12% of the world’sforests are presently in protected areas (FAO2001). The importance of maintainingbiodiversity in forest ecosystems has beenemphasized in the past 10 years at politicallevels through many international conven-tions and agreements promoting sustainableforest management (SFM) including theMontreal and Pan-European Processes, andat commercial levels as part of forest certifi-cation schemes (e.g., Forest StewardshipCouncil and Programme for the Endorse-ment of Forest Certification). Thus, biodi-versity is an issue of increasing relevance toplantation forests and their long-term sus-tainability; as a criterion for SFM, it is be-coming clear that maintenance of biologicaldiversity has direct implications for planta-tion forests and their management.

Biodiversity in a forest ecosystem is de-

Journal of Forestry • March 2006 65

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forest ecology

termined and influenced by climatic and soilconditions, evolution, changes in species’geographical ranges, population and com-munity processes, and natural or human-re-lated disturbances. Ecological processes andbiodiversity change over time as ecosystemsrecover from natural or human-induced dis-turbances. Disturbances can either increaseor decrease biological diversity dependingon the scales and measures of biodiversitybeing considered; for many measures, thehighest levels of biodiversity are found inforests that have been subjected to interme-diate frequencies, scales, and intensities ofdisturbance (Kimmins 2000).

Four components of biological diver-sity are of particular relevance to discussionson planted forests and their environmentalimpacts:

• Genetic diversity. The genetic varia-tion within a population or a species.

• Species diversity. The frequency anddiversity of different species in a particulararea or community.

• Structural diversity. How forest plantcommunities are structured both horizon-tally and vertically, which changes continu-ously as stand development proceeds and isparticularly significant in plantation forests.Structural diversity can be as important foranimal species diversity as is the diversity ofplant species in the forest plant communi-ties.

• Functional diversity. Variation infunctional characteristics of trees and otherplant species, i.e., evergreen versus decidu-ous, shade tolerant versus light demanding,deep-rooted versus shallow-rooted, andothers.

The aforementioned measures of bio-logical diversity can be applied at variousscales and are dynamic, changing over time.This change can be quite rapid, as a result ofdisturbance, or slow, as a result of climatechange or species evolution. Much of the

focus in discussions about biodiversity hasbeen at the species and local ecosystem level;however, biodiversity measures at this levelexhibit the greatest temporal variation.

In the following sections we will discussand attempt to summarize the current stateof scientific knowledge regarding the im-pacts of planted forests and their manage-ment on biodiversity. We will consider keyissues related to intraspecific diversity, focus-ing on genetic diversity within tree planta-tions, as well as the influence of planted for-ests on interspecific diversity within plantedforests and in surrounding landscapes. Inaddition, we will consider the role of biodi-versity in planted forests and the strategiesfor managing planted forests to conserve andenhance biological diversity at various spa-tial scales from the forest stand to the land-scape level.

Genetic DiversityCharacterization of Genetic Diver-

sity in Tree Plantations. As a fundamentalcomponent of global biodiversity, geneticdiversity includes the intraspecific variationbetween individual trees, e.g., genes, withinpopulations and between populations(races, ecotypes, and provenances). This ge-netic diversity largely controls adaptabilityand resistance to abiotic and biotic distur-bances.

In the past 10 years, the rapid develop-ment of tools (e.g., molecular markers) foranalyzing the genetic variability of foresttrees (Petit et al. 1997) has enabled scientiststo better characterize and assess pollen fluxesbetween individuals and populations, spatialdistributions of genetic diversity withinstands, and to better understand the effectsof silvicultural practices on the long-termevolution of genetic diversity of forest trees.Also, the molecular characterization of theplantation tree populations and improvedvarieties enable us to better manage and con-

trol the movements of forest reproductivematerials (FRM; Ribeiro et al. [2002]).

Modification of Genetic Pools (NewSpecies and Seed Transfer). Despite thegrowing body of scientific information avail-able to assess the possible impacts of planta-tions on intraspecific genetic diversity of for-est trees, broadly applicable generalizationsremain elusive. This impact is influencedclearly by the type of FRM used in planta-tions, the quality of available and registeredFRM genetic information, and the feasibil-ity of controlling gene exchange in the field.In addition, the impact of plantations ongenetic diversity depends on the level of ge-netic variability of the FRM itself, as well ason the possibility of gene exchanges betweenthe planted FRM and surrounding foresttree gene pools. At the regional forest treediversity level, the final impact of planta-tions established with a controlled FRM de-pends also on the total area afforested withthis FRM and duration of its use. A key chal-lenge for sustainable plantation forest man-agement is to anticipate, evaluate, and man-age risks posed by natural regeneration andspread of highly selected FRM outside ofplantation areas, especially hybrid, clonal, orgenetically modified (GM) varieties that are,initially, planned to be clearcut and re-planted.

As has occurred earlier in agriculture,the introduction of genetically improved ex-otic species in forestry increases productivityand carbon-fixation efficiency. In some re-gions these introductions also have increasedinterspecific diversity at landscape and re-gional scales. In France, e.g., compared with70 natural forest tree species, 30 introducedspecies are commonly used in plantation for-estry, which often helps to increase the inter-specific genetic diversity of forests at the lo-cal level (Le Tacon et al. 2000, 2001). Moregenerally, in Europe, the forest flora was verydiverse at the end of the tertiary period (ap-proximately 1.6 million years ago), and nu-merous species disappeared during succes-sive glacial periods. In Europe, at least, thereis no doubt that the introduction of newspecies has partly restored this species rich-ness.

Although popular in the past, introduc-tion of exotic species lately has been limitedin many countries because of greater con-cern about the risks associated with these in-troductions. Confirmation of long-term ad-aptation to environmental conditions(drought and frost resistance, tolerance tohydromorphic soil conditions, and so on)

Table 1. Plantation forests area by region, 2000.

Region

Total forestarea

(million ha)

Naturalforest area

(million ha)

Forestplantation area

(million ha)

Totalplantation area

(%)

Africa 650 642 8 4Asia 548 432 116 62Europe 1039 1007 32 17North and Central America 549 532 18 9Oceania 198 194 3 2South America 886 875 10 6World total 3869 3682 187 100

Source: FAO 2001

66 Journal of Forestry • March 2006

and pest resistance is necessary for the use ofexotic species in extensive plantation pro-grams, to avoid severe damage. Also, exoticspecies can have negative impacts on nativespecies and communities that need to beevaluated (Mack et al. 2000). For example,fast-growing species can replace native foresttree species because of their natural invasivepotential, as has been observed, e.g., witheucalyptus in northwestern Spain and Por-tugal.

Impact of Using Genetically Im-proved FRM. FRM collected from regis-tered seed stands results in plantation forestswith a level of genetic diversity most oftensimilar to the wild population from which itoriginates. The main genetic impacts de-pend on the level of adaptation of the intro-duced population to its new environmentand the possible gene transfers from it to thesurrounding native population. In this re-gard, the possible undesirable impacts oflong-distance seed transfer require specialconsideration. With the development of se-lection programs for plantation tree species,the level of genetic diversity of the plantedmaterial has been progressively restricted, aswith single or controlled mixtures of full-sibfamilies, clonal varieties, or GM trees thatmay be used in the future. Consequently,such FRM could be expected to have a loweradaptability and pose increased ecologicalrisks over the same rotation time (Gadgiland Bain 1999, Evans 1999, Wingfield1999). However, those risks may be mini-mized by adapting management practices,including the quick turnover of short-rota-tion tree crops if the FRM is not adapted.Also, the genetic information that has beenlargely developed in recent years allows theforest owner to better balance the expectedeconomic gains and the ecological risks, andthere are relevant and well-known breedingstrategies and gene conservation proceduresthat can facilitate maintenance of the geneticvariability of the plantation species over sev-eral generations.

Clonal Varieties. A major concern aris-ing from the use of clonal plantation forestryis the maintenance of stand adaptability, i.e.,the ability to face an unexpected cata-strophic perturbation due to biotic or abi-otic causes. Does the increased use of clonalplanting stock contribute to a decrease instand viability? What is the optimal numberof clones needed to minimize risks in clonalplantations? Although most regulations im-plicitly assume that planting more cloneswill minimize risks of plantation failure, the-

oretical investigations, based on simplifiedsituations in which susceptibility to pest at-tack is controlled by one single diallelic locus(Bishir and Roberds 1999), have shown thatthere is no single answer to those questionsand that risks can decrease, remain constant,or increase as the number of clones increases.To cover most situations, Bishir and Rob-erds (1999) recommend using clonal mix-tures including 30–40 genotypes, beyondwhich the level of risks is unlikely to changesignificantly.

GM Trees in Commercial Varieties. Cur-rently, gene transfer is being tested in mostforest species undergoing intensive breedingactivities (radiata pine, Scots pine, maritimepine, Sitka spruce, Norway spruce, eucalyp-tus, poplars, and others). In conjunctionwith other biotechniques such as somaticembryogenesis, rapid and important geneticgains can potentially be transferred to for-estry. Transgenesis has been considered as anattractive tool for genetically improvingtrees for pest and insect resistance, woodproperties, and lignin content (Jouanin2000). Benefits expected from transgenesisare increased ecological sustainability andeconomic efficiency of wood production byimproving and homogenizing target traits,increased adaptability and resistance to bi-otic and abiotic stresses, and reductions inthe use of undesirable insecticides and otherpesticides. For example, poplar, Europeanlarch, and white spruce have been engi-neered for a gene encoding an insecticidetoxin from the soil bacterium Bacillus thu-ringiensis (Bt). To date, there are a total of117 experimental plantations with GM treesbelonging to 24 trees species around theworld, but no commercial GM tree planta-tions have been reported. The main risks forbiodiversity (Kremer 2002) are related to thedissemination of GM material that mightresult in introgression with related tree spe-cies (Matthews and Campbell 2000) and inthe spread, through natural regeneration, ofGM trees that are potentially better adaptedto site conditions (Hayes 2001). As for an-nual crops, the potential use of transgenictrees in forestry has raised concerns in thepublic and among foresters and scientistsand has motivated vandalism and othercriminal acts. These unfortunate events il-lustrate the sharp controversy surroundingtransgenic trees that exists not only betweenthe public and the scientific community, butalso within the scientific community. Thereis an urgent need for an in-depth debate onbenefits and risks associated with transgenic

technology in forestry, considering scien-tific, economic, social, and ethical aspects.

Interspecific DiversitySpecies Diversity in Plantation For-

ests versus Naturally Regenerated Standsand Other Habitats. It is widely thoughtthat plantation forests, typically, are less fa-vorable as habitat than naturally regeneratedstands for a wide range of taxa, particularlyin the case of even-aged, single-speciesstands involving exotic species (Hunter1990, Hartley 2002). In support of this no-tion, the bird fauna of single-species planta-tion forests has been reported to be less di-verse than that of natural or seminaturalforests (Helle and Monkkonen 1990, Ba-guette et al. 1994, Gjerde and Sætersdal1997, Fischer and Goldney 1998, Twedt etal. 1999). Carabid beetles were found to bemore abundant and diverse in natural orseminatural forests than in spruce planta-tions in Ireland (Fahy and Gormally 1998)and Hungary (Magura et al. 2000). Similarresults were obtained in studies of beetles inSouth Africa (Samways et al. 1996), dungbeetles in Borneo (Davis et al. 2000), andarthropods in general in Brazil (Chey et al.1997) and New Zealand. The vegetation inconifer plantations was found to be less di-verse than that in seminatural woodlands inIreland (Fahy and Gormally 1998) and inGreat Britain (Humphrey et al. 2002).

However, we believe such findingsshould not be overgeneralized because insome cases the species diversity in plantationforests may be comparable with that in nat-urally regenerated stands. For example, spe-cies richness of indigenous birds in NewZealand was only slightly lower in pine plan-tation forests (Clout and Gaze 1984) and, insome cases, bird counts in these plantationsexceed those of most naturally regeneratedstands (Brockie 1992). Bird species richnessin a Lophostemon plantation in Hong Kongwas similar to that in secondary forests(Kwok and Corlett 2000). In Great Britain,the fungal and invertebrate communities inconifer plantations have been found to besimilar to those in natural woodlands(Humphrey et al. 1999, 2000, 2002).

The differences in species compositionand diversity between plantations and natu-rally regenerated stands can be attributed toa number of factors. The use of exotic treespecies in plantations has implications forindigenous forest species (Kholi 1998),which may have certain requirements thatare not met by the exotic tree species or the


habitat they create. For example, exotic treespecies in Britain are inhabited by far fewerherbivorous insects than are found in indig-enous forests (Kennedy and Southwood1984). By contrast, vascular plant speciesgenerally are not as discriminative and cancolonize plantation forests regardless of theidentity of the canopy species, provided thephysical characteristics of the habitat are ap-propriate. Some plantations can have ahighly diverse understory of indigenous spe-cies (Allen et al. 1995, Keenan et al. 1997,Oberhauser 1997, Viisteensaari et al. 2000,Yirdaw 2001, Brockerhoff et al. 2003).However, there is considerable variation inthe richness and abundance of understoryplants among planted forest stands. Some ofthis variation can be attributed to theamount of light available to understoryplants (Cannell 1999, Brockerhoff et al.2003), as illustrated in Figure 1. Particularlydense stands of spruce and Douglas fir cancast so much shade that they appear literallyto shade out the understory vegetation(Humphrey et al. 2002). Likewise, single-species plantations of Rhizophora (Figure 2)may prevent site colonization of other, non-planted mangrove species (Walters 2000,but see Bosire et al. 2003). In contrast, plan-tations with more open canopies have beenfound to have greater density, size, and rich-ness of woody species colonizing the under-story (Lemenih et al. 2004).

Generally, silvicultural and site man-agement practices in planted forests have di-rect impacts on stand dynamics and struc-ture and will greatly influence biodiversity.Intensity of site preparation, stand establish-ment, control of competing vegetation, pre-commercial or commercial thinning, prun-ing, methods, and timing of harvest largely

determine the rate of stand development,the initiation and duration of stem exclusionand other stages of stand development, andchanges in tree architecture and stand struc-ture. The harvesting method of clearcuttingplaces a strong constraint on species inhab-iting plantations and can dramaticallychange the species composition of under-story plants (Allen et al. 1995), although thesubsequent succession often restores the pre-clearcut understory vegetation (Brockerhoffet al. 2001). Fertilizer use can lead to reduc-tions in the populations of some native plantspecies but increases in the populations ofothers, especially if the site was degraded be-fore reforestation. Fertilization also may in-duce an increase in microbial diversity byaccelerating turnover of organic matter (Nys1999). There is limited knowledge of effectsof planted forests on the diversity of soilbiota compared with other land uses; it hasbeen shown that longer rotations foster soilbiodiversity for loblolly pine plantations inthe southeastern United States (Johnstonand Crossley 2002) and also that short-rota-tion plantations have positive effects on bi-ological soil fertility in the Congolese sa-vanna environment (Bernhard-Reversat2001). Herbicide or insecticide application,which often is associated with intensive

management of plantation forests, also canresult in a temporary decrease in plant,fungi, and insect biodiversity (Dreyfus1984). Short-rotation management also canreduce the quantity of dead wood that isbeneficial to saproxylic insect species (Jukeset al. 2002) or bryophyte species (Ferris et al.2000) and may decrease the opportunitiesfor colonization by poorly dispersed, late-successional native plant species (Keenan etal. 1997). Short rotations also will limit theextent to which structurally complex under-story development will occur, which canlimit the suitability of plantation for somewildlife species.

But such comparisons are not necessar-ily the most appropriate ones to make. Al-though the conversion of old-growth forests,native grassland, or some other natural eco-system to plantation forests rarely will be de-sirable from a biodiversity point of view,planted forests, in fact, often replace otherland uses including degraded lands. Wherethey are established on abandoned pasturesor degraded land, plantation forests usuallyare more beneficial to biodiversity than suchmodified agricultural areas. For example, inNew Zealand pasture is known to be domi-nated by exotic species and to be a particu-larly poor habitat for indigenous specieswhereas the understory of pine plantationsusually includes many indigenous plant spe-cies (Brockerhoff et al. 2001). In many cir-cumstances plantations may be the only eco-nomic means by which to overcome large-scale degradation. In these circumstances theissue is not whether to establish plantationsbut, rather, what kind of plantation to estab-lish.

Comparisons of plantations with othertypes of forests also are made more complexbecause the biodiversity in plantations de-pends very much on plantation age. Numer-ous studies performed during the past 15years have indicated that planted forests, in-cluding plantation monocultures, can accel-erate natural forest regeneration on de-graded sites where persistent ecologicalbarriers to succession would otherwise pre-clude recolonization by native forest species(cf. Parrotta and Turnbull [1997], Parrotta[2002]). This facilitative role of planted for-ests is due to their influence on understorymicroclimatic conditions, vegetation struc-tural complexity, and development of litterand humus layers during the early years ofplantation growth. This means biodiversitywithin plantations tends to increase overtime. Documented examples of the “cata-

Figure 1. Understory and plant species di-versity in low-density, third-rotation Pinuspinaster plantations in the Landes region ofGascony in southwestern France. (Photocourtesy of the European Institute for Culti-vated Forests/INRA, France.)

Figure 2. The use of dense spacing in treeplantings, such as these Rhizophora stylosa(mangroves) in the Philippines, reduces col-onization of nonplanted tree species andhinders biodiversity recovery. (Photo cour-tesy of Bradley Walters.)


lytic effect” of forest plantings on degradedlandscapes can be found in many tropical,subtropical, and temperate countries. In theMediterranean region, e.g., artificial forestscreated at the end of the 19th century torehabilitate overgrazed grasslands and forwatershed protection, and, subsequently,thinned and harvested, have reverted natu-rally to mixed conifer-broadleaf forests sim-ilar in structure and species composition tothose that existed before their degradationcaused by overgrazing, overharvesting, andfire. These examples highlight the need forconsideration of the land-use history whenevaluating species richness in plantation for-ests.

Characteristics of Species That CanBenefit from Planted Forests. As a habitatfor other species, plantation forests are char-acterized by some constraints resulting fromtheir more- or less-intensive management(see above). Clearcutting and comparativelyshort rotations favor the occurrence of rud-eral plant species whereas some long-livedclimax species may not be present, and har-vesting disturbance may enable invasive ex-otic plants to invade plantation forests(Allen et al. 1995). However, older standscan provide habitat for indigenous shade-tolerant species that are typical of the under-stories of naturally regenerated stands (cf.Allen et al. [1995], Brockerhoff et al. [2001];Figure 3). Similar patterns have been ob-served for birds (Clout and Gaze 1984), typ-ically for relatively common species. All suchspecies benefit from the additional habitatprovided by plantation forests if they havereplaced less-suitable habitat. Plantation for-ests also can accommodate edge-specialistspecies (Davis et al. 2000) and generalist for-est species that would benefit from any forest

type (Christian et al. 1998, Ratsirarson et al.2002).

Rare or threatened species often are notreported from plantation forests, but this isperhaps because of a lack of scientific study.Some notable cases of occurrence of suchspecies exist, and these often are significantfindings both as conservation issues and be-cause they can have implications for themanagement of plantations. For example,large populations of threatened kiwi inhabitsome pine plantations in New Zealand(Kleinpaste 1990). The occurrence of theseflightless endemic birds and other threat-ened species challenges plantation forestmanagers (Brockerhoff et al. 2001; Figure4). Another interesting case involves the crit-ically endangered ground beetle, Holcaspisbrevicula, a local endemic that has lost all ofits natural habitat, primarily to agriculturalland uses, and is today known to occur onlyin a plantation forest (Brockerhoff et al.2005).

Spatial Considerations. The role ofplantation forests in benefiting biodiversityat a regional level depends very much on thelocation of the plantation within the land-scape. In some circumstances, plantationforests can potentially have negative effectson adjacent communities because of invasivenatural regeneration of planted trees in adja-cent habitats (Engelmark 2001) or alterationof hydrologic properties and aquatic life inconnected watercourses through reductionsin water yield as a consequence of afforesta-tion or degradation of water quality by sed-iment movement generated from loggingtracks, newly constructed roads, or poormanagement practices of riparian strips(Maclaren 1996). On the other hand, theyalso can make an important contribution to

biodiversity conservation at the landscapelevel by adding structural complexity to oth-erwise simple grasslands or agricultural land-scapes and fostering the dispersal of speciesacross these areas (Hunter 1990, Parrotta etal. 1997, Norton 1998). Even plantationforests that are less diverse than naturally re-generated stands can increase bird diversityat landscape and regional scales, when theyhave habitat characteristics that are favoredby some species and are located in appropri-ate places (Gjerde and Sætersdal 1997). Inmost tropical regions, wildlife species (espe-cially bats and birds) are of fundamentalimportance as dispersers of seeds and soilmicroorganisms. Their effectiveness in facil-itating plantation-catalyzed biodiversity de-velopment on deforested, degraded sites de-pends on the distances they must travelbetween seed sources (remnant forests) andplantations, the attractiveness of the planta-tions to wildlife (ability of plantations toprovide habitat and food), and the conditionof the forests from which they are transport-ing seeds (cf. Wunderle [1997]). Plantationforests adjacent to exposed remnants of in-digenous forest therefore can be beneficialbecause they provide shelter, reduce edge ef-fects, and enlarge the habitat for some spe-cies, and they also can serve to increase con-nectivity among forest fragments (Norton1998). Such effects are most important inregions with sparse indigenous forest vegeta-tion.

Of course not all plantations generatebenefits such as these, and there still is muchuncertainty about just how these outcomesmight be achieved. Little is known, e.g., ofjust how much of a deforested landscapemust be reforested to allow biodiversity andself-sustaining forest ecosystems to be rees-tablished. Likewise, little is known of wheretrees might be replanted in a fragmentedlandscape to achieve an optimal biodiversityoutcome.

Plantations and Reduced Pressure onNatural Forests. It has been argued thatplantations may protect natural biodiversityindirectly by enabling greater wood produc-tion from smaller, intensively managed ar-eas, thus sparing remaining natural forestsfrom harvesting pressure (cf. Sedjo and Bot-kin [1997], Rudel [1998]). Wood produc-tion from plantation forests is growing rap-idly in many countries, yet there have beenfew attempts to assess whether such in-creased production actually has benefitednatural forests and their biodiversity (Cos-salter and Pye-Smith 2003). Mangrove

Figure 3. Plantation forests can have anunderstory of native plants, such as thesetree ferns in a 27-year-old Pinus radiatastand in New Zealand. In such stands, theterm “monoculture” only applies to the can-opy species. (Photo courtesy of EckehardBrockerhoff.)

Figure 4. A kiwi (Apteryx mantelli) in a pineplantation. These flightless birds are NewZealand’s biodiversity icon, and large pop-ulations occur in several plantation foreststhat provide suitable habitat for this threat-ened species. (Photo courtesy of Rogan Col-bourne.)


plantations in the Philippines have enabledsome reduction in harvesting pressure fromnearby natural stands (Walters 2004). InNew Zealand, the importance of plantationforestry as a means of producing wood prod-ucts has allowed the protection and conser-vation of indigenous natural forests; also, itis argued that through production and ex-port of roundwood, which usually is ob-tained from old-growth forests, New Zea-land plantation forests help to reduceexploitation pressure on old-growth forestsin other countries (Maclaren 1996). How-ever, a study of the Chilean forest industryfound the contrary: harvesting pressure onnatural forests actually increased as planta-tion production grew (Clapp 2001). In anycase, understanding the relationship be-tween plantations and natural forests is com-plicated by questions of timing and scale.There is a considerable time lag betweenwhen plantations are established and whenthey become producers of wood productsthat would otherwise be obtained from nat-ural forests and the more regional and globalmarkets for wood products there are, themore difficult it is to assess how changes inproduction from one forest impact produc-tion from others. These challenges notwith-standing, this is a topic that merits seriousattention from forest researchers.

Role of Biodiversity inPlanted Forests

It is well known that living organisms,through their metabolism and growth, driveenergy and matter flows that contribute tothe structuring and functioning of ecosys-tems. It is more difficult to understand howthe diversity of these organisms, i.e., speciesdiversity, affects these ecosystem processes.This question is a key issue in modern ecol-ogy but also has practical implications foragriculture and forest management. It is in-deed of great interest to understand howchanges in biodiversity can affect forest eco-system functions (e.g., primary productiv-ity, nutrient element cycling, soil fertility,and trophic interactions) that in turn canaffect crop yields.

Most of the experimental studies thatshow increasing biomass production withhigher species diversity have involved grass-land, wetland, or microbial species (Naeemet al. 1994, Yachi and Loreau 1999, Tilmanet al. 2002, Loreau et al. 2002). Because oftechnical difficulties in manipulating andmonitoring changes in biodiversity and eco-

system processes in systems dominated bylong-lived species such as trees, relatively fewcontrolled experiments have so far addressedthis issue in forests. To date, the results ofexperiments comparing biomass productionin single- and mixed-species plantations inboreal, temperate, and tropical regions havebeen inconsistent (cf. FAO [199], Petit andMontagnini [2004], Piotto et al. [2004],Pretzsch [2005], and Scherer-Lorenzen et al.[2005]), but the available data suggest thatmixed-species plantations may be more pro-ductive than plantation monocultures if (a)the planted species are more or less equallywell adapted to site conditions (so that onespecies does not dominate and ultimatelysuppress the other planted species), and (b) ifthe functional characteristics of the plantedspecies are sufficiently different; in particu-lar, if they exhibit significant temporal orspatial complementarity in their use of re-sources such as light, water, and soil nutri-ents (Figure 5). Where these conditions aremet, as in some (though not all) studies in-volving two-species mixtures that includednitrogen-fixing trees on N-limited sites, in-creased biomass yields have been observed

(Khanna 1997, Parrotta 1999, Binkley et al.2003, Forrester et al. 2005).

Diverse forests can be more resistant toinsect pests and diseases than single-speciesplantations, and thus the trophic dimensionof the biodiversity-ecosystem functioningrelationship needs to be considered. Severalreviews indicate that forest monocultures inall climatic regions may experience insectoutbreaks or pathogen epidemics that cancause considerable damage (Barthod 1994,Gibson and Jones 1977). Until recently, theevidence in support of the view that insectpest outbreaks occur more frequently inplantation forests as a result of their poortree species richness was controversial (Gad-gil and Bain 1999) because, in plantationforestry, confounding factors may occursuch as even-age structure (Geri 1980,Schwerdtfeger 1981), use of exotic species(Watt and Leather 1988, Speight and Wain-house 1989), and intensive silviculture (Rossand Berisford 1990, Jactel and Kleinhentz1997). However, a recent review, based on ameta-analysis of more than 50 field experi-ments that compared pure stand versusmixed stand of the same tree species, showeda significant increase in insect pest damage insingle-tree species forests (Jactel et al. 2005).Three main factors related to single-speciesforestry can predispose forest plantations toinsect attack (Jactel et al. 2005). First, thelack of physical or chemical barriers pro-vided by other associated plant species couldreduce access of herbivores to the large con-centration of food resources, i.e., the highdensity of host trees in the forest monocul-ture. Second, the low abundance or diversityof natural enemies often observed in forestplantations can result in limited biologicalcontrol of pest insects. A third factor is thepotential absence of a diversion process, i.e.,the disruption effect on pest insects resultingfrom the presence in the same stand of an-other more palatable host tree species. Asimilar review indicates that tree species di-versity also may make forests less susceptibleto fungal pathogens (Pautasso et al. 2005).For instance, damage caused by Melampsorarust disease, Heterobasidium annosum, andArmillaria root rot diseases are significantlylower in mixed than in pure stands. Twomechanisms are proposed to account for thisoverall tree diversity–pathogen resistance re-lationship: (i) in mixed forests, even if a spe-cies is severely affected by disease, other lesssusceptible tree species may replace the se-verely affected species and perpetuate theforest ecosystem, i.e., the “insurance hy-

Figure 5. A 60-year-old mixed plantation ofAraucaria cunninghamii and Flindersiabrayleyana in southern Queensland, Aus-tralia. Both species have similar growthrates on this site although the Araucaria ismore shade tolerant and has a deepercrown than the Flindersia. (Photo courtesyof David Lamb.)


pothesis” (Loreau et al. 2002), and (ii) be-cause most pathogens are passively dis-persed, the mixture of tree species will slowthe spread of disease (Pautasso et al. 2005).However, an important exception to the di-versity-resistance paradigm is the case ofpolyphagous pest insects and generalistpathogens. Populations of such organismscan first build up on a preferred host treespecies and then spill over onto associatedless palatable tree species, leading to a con-tagion process (Jactel et al. 2005).

Because of technical and economic con-straints, it is unlikely that plantation manag-ers will convert single-species stands intomixed-species stands simply to reduce pestdamage that is normally only of minor sig-nificance. On the other hand, they might doso if the commercially attractive tree specieswas especially valuable and the insect dam-age was significant. Keenan et al. (1995)described the advantages and requiredtradeoffs involved in using a temporary treecover crop to minimize tip borer attack inredcedar (a member of the Meliaceae) innorth Queensland. In this case insect dam-age on the target species was reduced in themultispecies plantation to an extent suffi-cient to make the plantation viable. On theother hand, the overstory canopy cover alsoreduced the growth rate of redcedar so thatcare had to be taken to balance survivalagainst growth increment.

Alternative ways of achieving the func-tional benefits of diversity might be to in-crease plant diversity in the plantation un-derstory, but proper field experiments areneeded to test whether this would be effec-tive. A second option might be to considerincreasing tree diversity at the landscapelevel. Growing evidence suggests that en-hancing habitat diversity in plantation forestlandscapes may prevent the development ofpest insect outbreaks. For example, a studyon spruce budworm, Choristoneura fumif-erana, reported lower balsam fir mortality instands surrounded by nonhost deciduousforest than in stands within large conifer-dominated forest (Cappucino et al. 1998).Similarly, Jactel et al. (2002) showed thatpure stands of maritime pine bordered by amixed woodland of broad-leaved species suf-fered fewer attacks by the stem borer Dioryc-tria sylvestrella than pure stands situatedwithin a monoculture of pine trees. Thesefindings indicate that the preservation or res-toration of mixed-species woodlands, e.g., ingaps where site conditions or stand accessi-bility make timber production less profit-

able, could provide the basis for a more sus-tainable management of plantation forests.

The role of biodiversity in modifyinghydrologic processes in plantation forests isunclear. There appears to be little evidencethat mixed-species plantations are any dif-ferent than single-species plantations interms of catchment water yields or waterquality. The most that can be said is thatfast-growing species tend to use more waterthan slow-growing species. On the otherhand, there is clear evidence that structurallysimple plantation monocultures withoutany significant understory or ground covercan foster significant erosion. Perhaps themost striking example is the heavy erosionthat can occur under pure teak (Tectonagrandis) plantations (Bruijnzeel et al. 2005).It also is possible that more diverse planta-tion systems might improve topsoil struc-tural properties such as infiltration ratesfaster than monocultures on badly degradedsites. There still is no strong experimentalevidence of this and any improvement islikely to take some time. Furthermore, anyconsequent decline in runoff and improve-ment in infiltration is likely to be masked bythe increased rates of evapotranspirationcaused by reforestation (Brujnzeel 2004).

Managing Planted Forests toEnhance Biodiversity:Suggestions for the Future

Genetic Resources. By combining sci-entific knowledge in forest and tree geneticswith commonsense forest management,general suggestions for preserving and en-hancing genetic diversity in plantation for-estry can be elaborated (Arbez 2000):

• Monitoring and improving geneticdiversity in breeding populations. The mainconcerns associated with the use of im-proved FRM are whether genetic gain anddiversity can be simultaneously maintainedat reasonable levels over successive genera-tions during the whole selection program.As many operational tree breeding programsconducted on fast-growing species are enter-ing their third or even more advanced gen-erations, these questions have raised theoret-ical and experimental approaches thatprovide guidelines to geneticists for main-taining genetic diversity (Namkoong 1988,Eriksson et al. 1993, White et al. 1993). Fur-thermore, conservation strategies can enrichthe genetic base at any moment and must beused as a necessary complement of thebreeding process.

• Controlling quality of FRM. Qualityof a given FRM is related directly to thequality of the genetic information available,allowing its final user to optimally balanceexpected gains and possible risks. It includesprecise and reliable information on (i) geo-graphic origin of the parent gene pool (nat-ural population or selected genotypes); (ii)identities, number, genetic characteristics ofthe parents, and crossing scheme used to ob-tain the commercial variety; and (iii) selec-tion procedures (description of the mono- ormultisite experimental design, selectedtraits, and levels of genetic superiority as-sessed by comparison with well-known re-producible standards). This information canbe used to control quality of FRM and tofavor FRM resulting from a long-termbreeding scheme combining recurrent selec-tion and gene resource conservation.

• Diversifying genetic resources at standor landscape levels through the parallel de-velopment of available genetically improvedvarieties and limited use of a given variety inspace and time to prevent genetic unifor-mity. The risks associated with improvedFRM and decreased genetic diversity can beminimized by (i) using multiclonal mosaicschemes, where genetic diversity within astand at a given time is replaced by geneticdiversity between stands at the landscapelevel; (ii) limiting the monoclonal planta-tion area at the regional scale as well as thetime during which a given clonal variety ispermitted to be used.

• Evaluating genetic risks, in particular,developing risk simulation methods and se-cured long-term trials to monitor impacts ofintroduction of GM trees in forest planta-tions before any commercial deploymentand use (Kremer 2002). Economic and bio-logical constraints limit the number of GMtrees created and impose to deploy themthrough clonal varieties. The main recom-mendations for their use include (i) male ste-rility, preventing pollen contamination ofthe surrounding forest-related tree species;(ii) testing not only in classical clonal tests(comparing one clone with a limited num-ber of standard other clones, in well-controlled conditions of experimental plan-tation) but also in long-term experimentalfield trials to evaluate environmental risks.

Stand Management. Enhancingbiodiversity in plantations can generally beachieved by increasing variability whenplantations are established or tended (Hart-ley 2002). The emphasis in the past has beenon reducing variability to improve predic-


tive capabilities and efficiency of establish-ment, tending, and harvesting operations.As a result, there is little experience with en-hancing variability in plantation manage-ment settings. It seems likely, however, thatmany future plantation owners, especiallythose operating on a small scale, will be seek-ing more than just timber production fromtheir plantations and might be willing totrade efficiency and predictability for thesake of ecological services such as enhancedbiodiversity.

This increased variability can beachieved in several ways. Perhaps the mostobvious is to use multispecies plantationsrather than monocultures. Random speciesassemblages are unlikely to be successful andcare is needed to design mixtures that arestable as well as productive (FAO 1992,Montagnini et al. 1995, Lamb 1998). Vari-ous planting arrangements have been testedbut alternate row plantings appear to be themost common. Plantations with more thanone species planted in alternate rows mayincrease yields and facilitate removal of theslower-growing species in an intermediatethinning. These mixed-species plantationsystems also may provide higher wood qual-ity through mutual shading of lower limbs(Oliver and Larson 1996). The choice ofspecies and the number to use in mixturesalso will be affected by economic consider-ations. One of the potential advantages ofdiversity is that it provides insurance againstfuture changes in market values but all po-tential species must have broadly similar val-ues; if not, the opportunity cost of reducingthe stocking of high-value species to use low-er-value species may be too high.

Managers can modify the silviculture ofplantations in other ways to enhance diver-sity. Small variations in the timing and typeof site preparation can affect the develop-ment and composition of the understory.How and if competing vegetation is con-trolled or the timing of thinnings also willaffect stand development (Figure 6). Be-cause diversity is enhanced usually by lowerdensity plantations, managers should try toavoid or minimize the process of stem exclu-sion where understory development is sup-pressed. Precommercial thinnings and com-mercial thinnings might occur earlier duringrotations and be more severe to enhance un-derstory development. Longer rotations alsowill favor the formation of a more diverseoverstory and encourage the development ofa more diverse understory. In coast Douglas-fir, rotations can be lengthened by thinning

without an appreciable drop in mean annualincrement (Curtis 1995). Another way ofachieving enhanced variability and diversityis by taking advantage of the “catalytic ef-fect” referred to earlier. In many areas, sin-gle-species stands may be the intention, butnatural regeneration of other species is inev-itable and adds to diversity (Lugo 1992, Par-rotta and Turnbull 1997). In these situa-tions, such as in the Douglas-fir region ofNorth America, this natural regenerationcould be encouraged during the vegetationcontrol process. Similar biodiversity en-hancement also could be achieved favoring adiverse plant understory (Chey et al. 1997,Lamb 1998). Given sufficient time, this un-derstory community may grow up and jointhe canopy layer. This means it could com-pete with the original plantation trees andreduce their productivity. Some of the man-agement options are reviewed in Keenan etal. (1997).

Even in plantation monocultures thereis considerable scope for enhanced variabil-ity. Less-uniform site preparation treat-ments, variations in tree spacing, and thin-ning treatments also can enhance standstructure variability. Structural complexityof the planted forest is an important deter-minant of subsequent biodiversity enrich-ment because of the importance of habitatheterogeneity for attracting seed-dispersingwildlife and microclimatic heterogeneity re-

quired for seed germination for a variety ofspecies (Parrotta et al. 1997). This suggeststhat broadleaf species yield generally betterresults than conifers, and that mixed-speciesplantings are preferable to monocultures,because of, in part, to their increased struc-tural complexity. Two-aged stands also maybe a viable alternative in situations whereclearcutting is esthetically unpopular. Ex-tending rotation length also could benefitbiodiversity, particularly favoring diversityof soil biota and species associated with deadwood or leaf litter (Ferris et al. 2000,Magura et al. 2000). Maintaining snags,logs, and other woody debris on site also canenhance habitat values for a range of species,from fungi to cavity-nesting birds. Manage-ment practices that increase soil organicmatter content (such as spot cultivation, useof amendments, or retention of harvest res-idues) and decrease soil disturbance duringsite preparation and harvest are desirable formaintaining the inherent biological capacityof soils and diversity of soil-living organisms,which are essential for nutrient conservationand cycling (Johnston and Crossley 2002).Although management efficiency may be re-duced, these more complex stand structuresmay be as productive, if not more produc-tive, than comparable even-aged plantations(O’Hara 1996). Although the productivityand actual effects on biodiversity of thesestructures are not well understood, there isadditional uncertainty with regard to cur-rent tree breeding and the appropriateness ofthese trees in complex forest structures.

Landscape Level. Forest managementneeds to consider plantations from a land-scape perspective in that they comprise aspatial array of different elements that can bearranged in different ways depending onmanagement goals. The key elements withina plantation forest are individual stands orcompartments of different age and speciescomposition; remnants of native ecosys-tems, including riparian strips; and amenityplantings. Observations suggest that manag-ing plantation densities and creating irregu-larities within the spatial structures, favoringthe proportion of borders and clearings, andpreserving natural plant communities alongrivers and in swampy areas would logicallyincrease the level of associated plant and an-imal biodiversity. Retention of broad-leavedspecies among coniferous plantations (Ferriset al. 2000), or preservation of native rem-nants, have been proposed as a managementtool to enhance biodiversity at the landscape

Figure 6. A coastal redwood (Sequoia sem-pervirens) plantation thinned heavily with ayounger cohort of sprout origin developingin the understory. (Photo courtesy of KevinO’Hara.)


level (Fisher and Goldney 1998, Norton1998).

Some of these elements are fixed in thelandscape (e.g., native remnants and ripar-ian strips) but others can be arranged in dif-ferent ways. Humphrey et al. (2000) sug-gested locating plantations near existingseminatural woodland fragments. In NorthAmerica, spatial modeling tools have beenused to optimize timber harvesting in nativeforests to meet biodiversity conservationgoals (Bettinger et al. 1997). Similar model-ing could be used to optimize the arrange-ment of different-aged plantation forestcompartments and different plantation spe-cies to maximize timber production, biodi-versity conservation, and ecosystem stabil-ity. Different spatial arrangements might beneeded where the aim is to modify hydro-logic processes (e.g., for salinity control).The key feature of this approach is that itconsiders biodiversity conservation at thelandscape scale rather than at the stand scaleand thus removes the direct conflict betweenbiodiversity conservation and timber pro-duction at any individual site. The majorpotential difficulty, of course, is that land-ownership patterns and consequently man-agement decisions often are made at the lo-cal rather than landscape scale. Therefore,ways must be found to ensure social out-comes as well as ecological outcomes at thelandscape level.

In his analysis of the role of industrialplantations in large-scale restoration of de-graded tropical forestlands, Lamb (1998)suggests a number of management ap-proaches by which forest productivity (andprofitability) and biodiversity objectivesmay be harmonized at the landscape level.These include increased use of native ratherthan exotic species, creation of species mo-saics across the landscape by matching spe-cies to particular sites, embedding planta-tion monocultures in a matrix of intact orrestored vegetation, using species mixturesrather than monocultures, or modifying sil-vicultural management practices to encour-age development of diverse understories be-neath plantation canopies (Figure 7).

ConclusionsThere is no single or simple answer to

the question of whether planted forests are“good” or “bad” for biodiversity. Plantationscan have either positive or negative impactson biodiversity at the tree, stand, or land-scape level depending on the ecological con-text in which they are found. Objective as-

sessments of the potential or actual impactsof planted forests on interspecific biologicaldiversity at different spatial scales require ap-propriate reference points. In this regard, itis important to consider in particular the(biodiversity) status of the site (and sur-rounding landscape) before establishment ofplanted forests and the likely alternative,land-use options for the site (i.e., would orcould a site be managed for biodiversity con-servation and other environmental servicesor be converted to agriculture or other non-forest uses?). For example, the establishmentof an industrial plantation on a particularsite will clearly have a more negative impacton stand-level biodiversity if it replaces ahealthy, diverse, old-growth native forestecosystem than if it replaces a degradedabandoned pasture system that was the re-sult of earlier forest conversion. Thus, theecological context of planted forest develop-ment, as well as the social and economiccontext shaping land-use change, must beconsidered in the evaluation of biodiversityimpacts (Romm 1989, Walters 1997, Rudel1998, Clapp 2001, Rudel et al. 2002, Sayeret al. 2004).

The need to pay more attention tobiodiversity issues in plantation design andmanagement is supported by observational,experimental, and theoretical studies that in-dicate that biodiversity can improve ecosys-tem functioning, i.e., it is not just the impor-tance of biodiversity per se but its role inimproving the overall resilience of the newecosystem. Although plantation monocul-tures have economic advantages, the need toensure their long-term sustainability arguesfor greater research effort to develop designand management strategies that enhanceplantation understory and soil biodiversity

as well as their functional benefits. Manyplantations are being established for the con-tribution they can make to overcome ecolog-ical degradation (e.g., soil salinity, erosion)and improve the long-term sustainability ofland uses such as agriculture. Faced with theunpredictable, enhancing species diversitymay improve adaptability of all managedforest ecosystems to changing environmen-tal conditions (Hooper et al. 2002).

The primary management objective ofmost plantation forests traditionally hasbeen to optimize timber production. Thiswill continue to be the primary objective inmost (although perhaps not all) industrialplantation programs but it will not necessar-ily be the case in many smaller-scale planta-tions owned by farmers and other nonindus-trial groups. In these circumstances themanagement objectives may place greaterweight on the provision of nontimber prod-ucts and ecological services such as biodiver-sity. This will require the development of anew range of silvicultural tools to establishand manage these plantations.

Where managers are seeking to producegoods as well as ecological services, there are,invariably, difficulties in making the neces-sary tradeoffs. These tradeoffs operate at alllevels of biological diversity. In the case ofgenetic diversity, e.g., a balance must bestruck between the need to identify the mostproductive FRM to plant at a particular siteand the desire to reestablish the biodiversityrepresented in the original genotypes.Should a manager use highly productiveplanting material with a narrow genetic basethat has been developed from an intensiveselection program, clonal material, or evenGM varieties? Or, should one rely instead onnatural seed sources with a wider genetic di-

Figure 7. Understory management practices can have a profound effect on biodiversitydevelopment in plantations, as illustrated in the two young (<10 years old) eucalyptplantations in Vietnam. In the stand on the left, twigs and leaves are regularly swept up forfuel. In the stand on the right, fuel collection is excluded, allowing understory regenerationof native flora. (Photos courtesy of David Lamb.)


versity because these may confer greater re-silience to the plantation, enabling it to copebetter with future environmental changessuch as insect attacks or climatic events? Ju-dicious use of relevant, well-known tree-breeding strategies and gene conservationstrategies can greatly facilitate efforts bymanagers to maintain genetic variability ofplantation species over several generationsand thus achieve better balance between eco-nomic and environmental benefits and risks.

Likewise, at the species level, shouldmanagers establish plantation monoculturesor should they give greater emphasis to mul-tispecies plantations? There are, of course,no simple answers to questions such as thesebecause much depends on the fertility of thesoils being planted (are they still able to sup-port the original native species and the soilbiota required for maintaining soil fertilityand nutrient cycling processes?) and on thepresent objectives of the landowner. Usu-ally, some compromise between the two ex-tremes is chosen.

A critical issue for the future of planta-tion forests is how to combine biodiversitymaintenance and wood production at vari-ous spatial scales, i.e., at stand, forest, andlandscape levels (Spellerberg and Sawyer1996). One way to achieve a balance be-tween biodiversity and productivity/profit-ability is through improved practices at thestand level or alternative silvicultural re-gimes (species mixture at different scalesfrom individual trees to compartments ofdifferent sizes, age, and clone mosaic) com-bined with biodiversity management atlandscape level. This would include, e.g.,modification of extensive clearcut practicesto reduce group or patch sizes (i.e., plan forsmaller compartments of same-aged standsthat are dispersed within the plantationlandscape) to achieve a better balance be-tween economic and environmental objec-tives. Thus, it may be possible to achieve adegree of biodiversity at the landscape scalethrough diversification of plantation land-scapes to create mosaics of different plantedforest and natural vegetation habitats, evenif each of the individual plantation standswithin that landscape are established as sim-ple monocultures. In many parts of theworld, this will require a reorientation ofcurrent practices and, in particular, a shiftfrom a stand-level to a forest- or landscape-level approach to the planning of all aspectsof plantation management.

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Jean-Michel Carnus ([email protected]) is director, Forest and Wood Research Site,Institut National Recherche Agronomique(INRA), Pierroton, 33610 Cestas, France.John Parrotta ([email protected]) is nationalresearch program leader for International Sci-ence Issues, USDA Forest Service-Research and


Development, 4th floor RP-C, North KentStreet, Arlington, VA 22209 Eckehard Brock-erhoff ([email protected]) issenior scientist in the Forest Health and Biodi-versity group at Ensis, University of Canter-bury, P.O. Box 29237, Fendalton,Christchurch, New Zealand. Michel Arbez([email protected]) is honorary president, In-stitut Europeen de la Foret Cultivee, 33610,Cestas, France. Herve Jactel ([email protected]), is director, Forest Entomol-ogy Laboratory, Institut National RechercheAgronomique (INRA), Pierroton, 33610 Ces-tas, France. Antoine Kremer (antoine.

[email protected]) is director, Biodi-versity Research Unit, Institut NationalRecherche Agronomique (INRA), Pierroton,33610 Cestas, France. David Lamb([email protected]) is associate pro-fessor, School of Integrative Biology, Universityof Queensland, Brisbane, Queensland 4072,Australia. Kevin O’Hara ([email protected]) is professor of Silviculture, De-partment of Environmental Science, Policyand Management, University of California,Berkeley, CA 94720-3114. Bradley B. Walters([email protected]) is associate professor of Ge-ography and Environmental Studies, Mount

Allison University, Sackville, New Brunswick,Canada E4L 1A7. An earlier version of thisarticle was presented at UNFF IntersessionalExperts Meeting on the Role of Planted Forestsin Sustainable Forest Management, Mar. 24–30, 2003, New Zealand. Buck, A., J. Par-rotta, and G. Wolfrum (eds.). 2003. P. 33–49in Science and technology—building thefuture or the world’s forests and planted for-ests and biodiversity. International Union ofForestry Research Organisations (IUFRO) Oc-casional Paper No. 15. International Unionof Forest Research Organizations, Vienna,Austria.


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