the application of forestry principles to the design, execution and...

B O I S E T F O R Ê T S D E S T R O P I Q U E S , 2 0 0 2 , N ° 2 7 3 ( 3 ) 5SYLVICULTURE / MANGROVES

DOSSIER

Photo 1. Mature stands of Sonneratia alba on the cyclone-prone Kimberley coast of northwestern Australia. Photo P. Saenger.

Whether the motives are economic, practical or aesthetic, the success ofany mangrove planting programme can be enhanced by the application of sound forestryprinciples and practices. These apply to all phases of the operation, from selection of suitablegermplasm, to its macro- or micropropagation, site-species matching, selection of plantingdensities, and assessment of stand performance.

Brett J. Stubbs

Peter Saenger

School of Environmental Science and ManagementSouthern Cross UniversityPO Box 157, Lismore, New South WalesAustralia, 2480Tel: (61-2) 6621 3650Fax: (61-2) 6621 2669email: [email protected]@scu.edu.au

The application of forestryprinciples to the design,

execution and evaluationof mangrove restoration

projects

RÉSUMÉ

LES PROGRAMMES DERESTAURATION DES MANGROVES :APPLICATION DES PRINCIPES DE LAGESTION FORESTIÈRE POUR LEURCONCEPTION, LEUR RÉALISATIONET LEUR ÉVALUATION

Des programmes de reboisement dela mangrove sont réalisés aujourd’huidans de nombreux pays du monde,que ce soit pour des raisons écono-miques (production de bois d’œuvre,développement de la pêche), écolo-giques (protection et stabilisationdes littoraux et des canaux côtiers,restauration et protection des écosys-tèmes et de la vie sauvage) ou poli-tiques (évolution des législations,développement social). La définitionprécise des objectifs et des prioritésde chacun de ces programmes estessentielle pour assurer leur bondéroulement et leur évaluation.L’application d’une gestion forestièresaine, à toutes les étapes de leur réa-lisation, est aussi la clef de leur réus-site : du contrôle des caractéristiquesgénétiques des plants à l’applicationraisonnée des techniques de macro-ou micro-propagation, de l’adéqua-tion entre choix des espèces et carac-téristiques écologiques des sites ausuivi de la densité des plantations età l’évaluation des résultats.

Mots-clés : mangrove, valorisation,restauration, gestion forestière, pro-tection du littoral.

ABSTRACT

THE APPLICATION OF FORESTRYPRINCIPLES TO THE DESIGN,EXECUTION AND EVALUATION OFMANGROVE RESTORATIONPROJECTS

Mangrove planting is carried out inmany parts of the world for a greatvariety of reasons, including timberproduction, shoreline protection,channel stabilization, fisheries andwildlife enhancement, legislativecompliance, social enrichment, andecological restoration. Clear defini-tion and prioritization of the objec-tives of any planting programme isessential to its planning, executionand evaluation. Whether the motivesare economic, practical or aesthetic,the success of any mangrove plantingprogramme can be enhanced by theapplication of sound forestry princi-ples and practices. These apply to allphases of the operation, from selec-tion of suitable germplasm, to itsmacro- or micropropagation, site-species matching, selection of plant-ing densities, and assessment ofstand performance.

Keywords: mangrove, value, restora-tion, forestry, silviculture, coastal pro-tection.

RESUMEN

LA APLICACIÓN DE LOS PRINCIPIOSDE MANEJO FORESTAL PARADEFINIR, REALIZAR Y EVALUAR LOSPROYECTOS DE RESTAURACIÓN DELMANGLAR

Se efectúan plantaciones de mangla-res en distintos puntos del planetapor múltiples razones, entre las quese incluyen la producción de maderade construcción, la protección cos-tera, la estabilización de los canales,la mejora de las pesquerías y de lavida salvaje, la conformidad con lalegislación, el enriquecimiento socialy la restauración ecológica. En cual-quier programa de plantación, definirclaramente los objetivos y establecerlas prioridades es esencial para suplanificación, ejecución y evaluación.Aunque las motivaciones sean decarácter económico, práctico o esté-tico, el éxito de cualquier programade plantación puede verse favorecidopor la aplicación de algunos princi-pios y prácticas de manejo forestalsano. Esto se aplica a todas las fasesde la operación, desde la selección degenomas adaptados hasta la macro omicropropagación, las elecciones deasociaciones sitio-especie, de densi-dades de plantación y la evaluacióndel desempeño del rodal.

Palabras clave: manglar, valor, res-tauración, manejo forestal, silvicul-tura, protección costera.

6 B O I S E T F O R Ê T S D E S T R O P I Q U E S , 2 0 0 2 , N ° 2 7 3 ( 3 )

MANGROVES / FORESTRYDOSSIER

Brett J. Stubbs

Peter Saenger

In the 1830s, the acclaimed natu-ralist Alexander von Humboldtdescribed South American mangrovesin the following terms: “the mangletrees produce miasmas… all settlers inthe tropics are well familiar with thenoxious perspirations of those plants.They attribute the unhealthy air to theroot-stocks of the mangle trees… weassume that chemical gases are gen-erated which defy all chemical investi-gations.” Such negative perceptionsof mangroves persisted well into thelate twentieth century, representingthe mangroves at least as a nuisance,if not as downright dangerous and sin-ister. With increasing knowledge, theycame to be viewed as interesting sci-entific curios. Later a more utilitarianview became prevalent. Increasinglytoday, mangroves are being protected,managed and restored because oftheir perceived value in providingproducts and services.

The values of a mangrove sys-tem (photo 1) are manifold, but fourbroad categories can be identified:economic, usefulness, intrinsic andsymbolic values. Economic values arereadily recognized in the direct andindirect products obtainable frommangroves. Direct products consist ofvarious wood products (photo 2) andrelated materials such as tan-barkand fodder, while indirect productsinclude fish, crustaceans, shellfishand honey. These economic valuescan easily be quantified as, for exam-ple, the annual value of a mangrovefishery or timber yield (table I).

Usefulness values (also referredto as “instrumental values”, “freeservices” or “ecological functions”)include the provision of habitat,shoreline protection, chemical buffer-ing, water quality maintenance, recre-ational and education opportunities,and reservoirs of genetic material.These values are difficult to quantifyin monetary terms.

The acceptance of intrinsic val-ues, i.e. that organisms, communitiesand ecosystems have an inherentright to exist independently of anyhuman interest in them, is becomingmore widespread. Such a view forms

the basis of much of the rationale ofthe conservation and animal welfaremovements and underpins our effortsat heritage and biodiversity conserva-tion. Since these values cannot bequantified (and, perhaps, should notbe), they are often overlooked.

Symbolic values, derived fromreligious, totemic or mythical beliefs,are probably attached to many man-grove areas by indigenous people.Thus, the sacred groves in India, thesacred sites of the AustralianAborigines, or the fetish forests ofBenin, represent areas of considerablesymbolic value to their custodians.While such values may be rather diffi-cult for non-believers to understand orappreciate, they should not be over-looked. As with intrinsic values, sym-bolic values cannot be quantified.

Using an alternative scheme, itis also possible to assess the value ofmangrove communities in terms oftheir components, functions andattributes (table I I). Componentshave a direct use value which can beassessed on the basis of costs (i.e.labour expended both as paid labourand as labour time) and prices; func-tions are indirect use values whichsupport other activities and can beassessed on the basis of replacementcosts or the value of the damageavoided; and attributes are qualitiesthat have a non-use value eventhough they may also contribute todirect and indirect use values.

Mangrovesilviculture

and restoration

The basis of mangrove plantingtoday may be economic, practical, oraesthetic (photos 3 and 4). Objectivesmay include timber production,shoreline protection, channel stabi-lization, fisheries and wildlifeenhancement, legislative compliance,social enrichment, or ecologicalrestoration. For example, in countriessuch as Bangladesh, Indonesia,Malaysia, Thailand, and Myanmar(Burma), there are large commercialmangrove forestry operations whichrequire the replenishment of har-vested mangrove stands. In China,Vietnam, and Bangladesh, mangrovesare planted for purposes of stabiliz-ing and protecting the coastline andcoastal towns and villages fromcyclone damage and seawater intru-sion. Mangrove plantings are alsoundertaken to provide amenity val-ues or to augment the ecologicalfunctioning of prawn (Philippines andIndonesia) and fish ponds (India). Theremainder of this article examines thevarious reasons for mangrove plant-ing and then considers how forestryprinciples can be applied to thedesign, execution, and evaluation ofthose plantings in order to meet theiroriginal objectives.


DOSSIER

Photo 2. Debarking of Rhizophora mangle and R. harrisonii near Corinto, on the Pacific coast ofNicaragua. These poles are used for construction and the removed bark is not used further. Photo P. Saenger.

Introduction

Objectives for mangroveplanting

It is essential that objectives beclearly defined and prioritized as afirst step in the mangrove plantingprocess. The coastal afforestationproject in Bangladesh, for example,has several objectives, the foremostof which are the production of com-mercial timbers, acceleration of therate of accretion of new land areas,and improvement of the protection ofnearshore agricultural and residentiallands from storm damage (Saenger,

Siddiqi, 1993). All of these objectivesare being achieved, but in some situ-ations, success in achieving oneobjective has meant less success inachieving another. For example, treeswere buried and timber productionwas negligible in planting sites wherevery high sedimentation rates occur.In assessing the significance of highsedimentation rates at particularsites, it is important to determinewhether the production of timber orthe reclamation of new land has thehighest priority.

Clearly, if timber production ismost important then sites likely toexperience high sedimentationshould be avoided or the first plant-ing should be considered as sacrifi-cial, serving solely to help raise theland to the point where another moredesirable species would survive. Ifstabilization and reclamation areparamount, then the burial of an ini-tial plantation by sediment should beregarded as a success, and replantingshould be undertaken to extend thegains already made.

Prioritized objectives underpinthe planning process; they help toidentify the elements which must beincluded to provide the undertakingwith a clear framework for operationand implementation. They are alsoessential for evaluating the extent ofsuccess of the planting project.



Table I. Estimates of the economic value of mangroves. No corrections have been madefor time-related fluctuations in the US$. (After Saenger, 2002).

Country Year Value Yield or benefit(US$/ha/year)

Traditional goodsPNG 1977 1 Crocodile skins, game

Benin 1989 12 Salt production

Indonesia 1990 33 Traditional products

Indonesia 1992 33 Traditional products

Thailand 1982 230 Traditional products

Philippines 1984 650 Alcohol from Nypa

Forest productsFiji 1976 6 Timber and fuelwood

Indonesia 1990 66 Chipwood production

Indonesia 1992 67 Timber, fuelwood and chipwood

Trinidad 1974 70 Timber and fuelwood

Malaysia 1984 110 Fuelwood

Malaysia 1985 150 Charcoal

Philippines 1996 151 Timber and fuelwood

Thailand 1982 230 Nypa shingles

Thailand 1985 500 Timber and fuelwood

Malaysia 1986 566 Timber and fuelwood

Aquaculture after mangrove conversionIndia 1986 -145 Extensive shrimp production

Philippines 1978 -180 Milkfish (Chanos chanos)

Thailand 1982 -206 Extensive shrimp production

Ecuador 1982 -390 Extensive shrimp production

Philippines 1979 -1 600 Intensive shrimp production

Thailand 1982 -2 106 Intensive shrimp production

Philippines 1996 -7 124 Aquaculture

Fisheries productsPhilippines 1996 60 Mangrove fisheries catch

Thailand 1982 30 Small-scale fisheries

Fiji 1976 100 Mangrove fisheries catch

Indonesia 1992 117 Mangrove fisheries catch

Trinidad 1974 125 Small-scale fisheries

Thailand 1977 130 Wild-caught shrimps

Fiji 1985 166 Small-scale fisheries

Indonesia 1977 1 010 Wild-caught shrimps

Malaysia 1982 2 770 Mangrove fisheries catch

Agriculture after mangrove conversionIndia 1984 -35 Coconut

Fiji 1976 -52 Agricultural production

Senegal 1984 -80 Rice

Thailand 1983 -165 Rice

Indonesia 1992 -220 Rice

Ecosystem servicesIndonesia 1992 3 Erosion control

Indonesia 1992 15 Biodiversity conservation

Trinidad 1974 200 Ecotourism park fees

Fiji 1976 5 820 Polishing treated sewage

Timber production

Mangrove silviculture and tim-ber extraction (photo 5) has a longhistory, formalized by the colonial for-est departments of the Europeanpowers that usurped tropical lands.Thus, Dutch, Belgian, French,Spanish, German, Portuguese andBritish colonial forestry agenciesmanaged many mangroves of Africa,South America and Australasia, gen-erally on the management constructsof the spruce and oak forests ofEurope, and always with the need forcolonial advancement firmly at theforefront of their organisationalobjectives. While some of these man-grove forestry projects have beenoustandingly successful (e.g. Matang,Malaysia; Chan, 1996), others haveexperienced problems.

Shoreline protection,channel stabil ization and

storm protection

Because of their intricate above-ground root systems, mangrovesreduce the velocity of waters flowingthrough and around them. Such areduction in water velocity gives thema significant role in coastal protectionand there are numerous examples ofmangrove plantings that were specifi-cally undertaken for such purposes(photo 6).

Early last century, there wereproposals to stabilize the banks ofthe newly constructed Suez Canaland the North African shorelines gen-erally with Rhizophora spp., based onthese mangrove characteristics. Morerecently, in 1966, a coastal afforesta-tion programme was initiated inBangladesh specifically to protectcoastal villages from surge and stormdamage during the frequent cyclonesthat sweep into the Bay of Bengalduring the monsoon season(Saenger, Siddiqi, 1993). The effec-tiveness of these mangrove planta-tions in stabilizing newly depositedsediments in the Bay of Bengal is con-firmed by the fact that 160 000 ha ofmangrove plantations have beenestablished over the past 35 years.


DOSSIER

Photo 3. A twelve-year-old plantation of Sonneratia apetala for the dual purpose of timber production and coastal stabilization. Bangladesh. Photo P. Saenger.

Table II. Values of mangroves as components, functions, and attributes.(Source: Saenger, 2002).

Components Plant resources

Fisheries resources

Wildlife resources

Water supply resources

Agricultural resources(incl. salt production and aquaculture)

Forage resources

Water transport resources

Recreational resources

Energy resources

Pharmaceutical resources

Functions Shoreline protection

Windbreak and storm protection

Sediment regulation

Nutrient retention

Water quality maintenance

External support

Groundwater discharge and recharge

Local microclimatic stabilization

Attributes Biodiversity

Uniqueness and heritage

Fisher ies and wildli feenhancement

Where mangroves have beendepleted, there may be an associateddecline in nearshore productivitywhich, in turn, may prompt a man-grove replanting programme. Bacon

(1993), for example, reports theincrease of waterfowl usage of wet-lands in the Caribbean following man-grove enhancement through a plant-ing programme.

Legislative compliance

In many countries with man-groves, strict protective measureshave been implemented, and com-pensatory requirements also oftenexist. In most Australian states, man-groves are protected and mangrovelosses resulting from public activitiesmust be legally compensated for bythe planting of similar areas. In Ballina(New South Wales), for example, there-alignment of a major arterial roadthrough a mangrove communitycaused a net loss of 7 hectares, andan equivalent area of coastal land wasset aside to be replanted with man-groves to offset the ecological lossessustained. Such “no net loss” policiesare increasingly being used by land-use management agencies.

Social enr ichment

Planting for social enrichmentcovers a wide variety of objectives,ranging from aesthetics to incomegeneration through eco-tourism. Inthe Middle East, for example, wheregreen vegetation is scarce, the plant-ing of mangroves is viewed as anachievable means of “greening” andbeautifying the landscape. In theUnited Arab Emirates, mangroveplanting programmes have beenongoing since the late 1970s.Although the only objective there hasbeen to provide a green backdrop toan otherwise stark landscape, theplantations have not only met thatobjective but have provided addi-tional benefits such as roosting andfeeding sites for migratory waders,flamingoes, and a range of otherwildlife.

In any programme aimed atsocial enrichment, it is important thateconomically impoverished peoplewho depend on the direct exploita-tion of mangroves for their livelihoodobtain benefits from the planting pro-gramme. A replanting programme canbe used to improve the economicopportunities and well-being of ruralpeople by providing direct employ-ment for them in the planting pro-gramme, by restoring the productivity

of lands and ecosystems they use,and by increasing the diversity ofplants and animals they harvest.

Ecological restoration

Although mangrove restorationhas recently become topical, suchprojects, in one form or another, havebeen around for many years. Some ofthe earliest mangrove harvesting pro-grammes included replanting condi-tions (e.g. in the Belgian Congo, nowZaire; Pynaert, 1933). Walters

(2000) reports on village-based man-grove restoration programmes in thePhilippines going back for 90 years.Nevertheless, there is now increasingawareness of the benefits of ecologi-cal restoration of mangroves afterdegradation or destruction by humanactivities or natural phenomena.

One of the driving forces behindthe restoration of mangrove ecosys-tems to something like their pre-

Photo 5. In the Matang Forest Reserve,timber harvesting is in alternatingrectangular parcels to ensure thatmature mangroves surround thecleared area. Photo P. Saenger.

Photo 4. Fish traps in the Nypa fruticans swamps of southern Sulawesi, Indonesia. Photo P. Saenger.



sumed original states is the spectacu-lar rise in environmental conscious-ness over the past 30 years. Therestoration of mangrove lands forconservation remains a matter ofchoice and, while such choice shouldbe determined by the socio-economicpriorities of the communities invol-ved, more often it is influenced byexternal pressure from conservationorganisations advocating the preser-vation of nature (Field, 1999).

Another important driving forcefor mangrove restoration is the world-wide depletion of mangrove resour-ces through increasing population(especially in coastal areas), foodproduction, industrial and infrastruc-tural development, excessive extrac-tion of materials and chemical con-tamination and hydrological alter-ation of mangrove land (Hamilton,

Snedaker, 1984; Field, 1996).Lewis (1982) was one of the first

to advocate planting mangrovesspecifically for the environmentalservices they can provide. One of thenecessities of such an approach is toavoid monocultures of mangrovesthat still frequently characterize tim-ber production. Most restoration proj-ects, however, are still mainly basedon one or two species. Nevertheless,a number of restoration programmeshave achieved a degree of ecologicalfunctioning similar to natural man-grove systems (Mc Kee, Faulkner

2000).

Project success

Two main types of criteria aregenerally used in judging the successof a mangrove planting programme:(1) the effectiveness of the planting,which can be considered as the close-ness to which the new mangrove for-est meets the original objectives of theplanting programme; and (2) the effi-ciency of the planting, which can bemeasured in terms of the amount oflabour, resources and materialinvolved during the establishment andmaintenance phases (Field, 1999).

A major objective of any restorationprogramme should be to facilitatenatural regeneration and to select tar-get areas where some assisted regen-eration is feasible and needed.Secondary objectives might includethe enhancement of growth of exist-ing mangroves and the selectiveintroduction of additional speciesinto the community.

Moreover, success with anymangrove restoration is considerablyenhanced when (1) restoration isviewed by local people as offeringthem economic or other tangible ben-efits; (2) restoration is compatiblewith local patterns of resource useand land tenure; (3) local knowledgeand skills relevant to restoration aresuccessfully embedded in the proj-ect; (4) local social groups and organ-izations are effectively mobilized tosupport and implement restorationactivities; and (5) relevant policiesand political factors are supportive ofrestoration efforts.

Macropropagationof mangroves

Once objectives have beenestablished for mangrove planting ina particular area, locating and propa-gating suitable germplasm is the nextphase. Several approaches have beenadopted for macropropagation ofmangroves, including the following.

Direct planting of propagulescollected from the wild

As propagules are generallyonly available for 2-3 months of theyear, direct seeding needs to bescheduled according to seasonalavailability. Spacing distance is diffi-cult to control but distances from 0.4-1.5 m have been used. The generallyhigh susceptibility of propagules todesiccation, dislodgment by wavesand tides, and damage by predatorsand debris, make this material unsuit-able for sites of medium to highenergy. Hamilton, Snedaker (1984)suggest that planting of propagulesshould be carried out during coolweather and on flood-free days.


DOSSIER

Photo 6. A seawall with a protective mangrove fringe of Kandelia candel encloses arableland adjacent to the Juilong estuary in Fukien Province, southern China. Photo P. Saenger.

Outplanting of up to one-year-old nursery-raised propagules

Propagules of different speciescan be collected during the fruitingseason and then grown on freelydrained sandy substrate. For mostspecies, the soil should be keptdamp, preferably with 25-50% sea-water (to reduce fungal infection).Relatively high temperature andhumidity are essential for mangrovegrowth. Indirect sunlight is moreeffective than direct sunlight in pro-ducing a large leaf area (Youssef,1997). As mangroves respond to fer-tilizers in early stages, fertilizer canbe added once roots have started todevelop and the first pair of leaveshave expanded. This has resulted ingreater root growth and healthiershoots (Youssef, 1997).

The benefit of raising seedlings innurseries (photos 7 and 8) is that ayear-round supply is available, which isof particular importance in large-scaleprojects (Saenger, Siddiqi, 1993;Field, 1996; Youssef, 1997). Nursery-grown seedlings also generally show

higher success rates (survival rates,increases in height, number of leaves)than propagules (Saenger, Siddiqi,1993), although nursery costs andincreased planting difficulties whencompared to propagules may some-times offset these advantages.

Direct transplanting ofseedlings and shrubs

Where young seedlings areremoved from a natural mangrove for-est and transplanted to sites underrehabilitation, the most commonseedling height is <50 cm. Youngseedlings are best removed by usinga 10 cm PVC pipe as a corer, pushed20-25 cm into the substrate aroundthe seedling. Transplants should bekept moist and protected from directheat and wind during collection andtransportation.

Few reports have described tri-als of transplantation of young man-grove trees from natural forests. Theextensive root system of young man-grove trees offers the promise ofgreater and faster success of estab-

lishment than could be expected fromseedlings. These individuals wouldtherefore have a higher resistance towave erosion and debris and can betransplanted into sites of higherenergy where propagules or seedlingsare unlikely to survive.

Outplanting after nursery-raising small seedlingscollected from the wild

Where propagules are unavail-able, newly-established seedlingshave been used to establish nurserystock. The seedlings are dug out,washed free of soil, and replanted inacid-washed coarse sand. With thisapproach, the advantages of bothnursery-raised seedlings and smallseedling transplantation (<50 cm)have been combined. Damage to thedonor site can been avoided by usingsmall seedlings. The technique canalso reduce the time required forpropagules to grow to the height (50-70 cm) where a high survival ratecould be expected after transplanta-tion in the field (Youssef, 1997).



Photo 7. Intertidal nursery beds inBangladesh for raising Sonneratiaapetala seedlings for subsequentplanting out in the coastal areas. Photo P. Saenger.

Photo 8. Municipal nursery for Dubai, UnitedArab Emirates, raising mangroveseedlings for use in landscapebeautification. Photo P. Saenger.

Raising of air- layeredmater ial

Air-layering involves the removalof short sections of bark and phloemof mature lateral branches until thecambium becomes exposed. Theinjured area of the stem is thenwrapped with Sphagnum moss orsimilar material in aluminium foil toretain moisture. After roots havedeveloped, the stem is then cut belowthe layering area to form a new plant.

Unlike raising young seedlings,the air-layering method reduces therisk of root damage by insects and crustaceans, especially in the early

stages of establishment. However,the technique utilizes mature treesin the field, and is thus subject tomany other biotic and abiotic vari-ables that cannot be controlled (e.g.fungal and bacterial infection, fluctu-ation in temperature and rainfall,and tide height). Most importantly,the technique is relatively expensive(Carlton, Moffler, 1978).

Use of stem cuttings

Mangrove stem cuttings can beinduced to form roots after treatmentwith various growth hormones(Basak et al., 1995; Youssef, 1997).Eganathan et al. (2000) reported thelarge-scale propagation of Excoecariaagallocha, Heritiera fomes and Intsiabijuga using cuttings and air-layers.

Use of propagulesegments

In the early 1980s, Thai forestersdeveloped a method of cutting vivipa-rous propagules of Rhizophora apicu-lata into segments, generally three,and planting each segment sepa-rately. Many of these segmentsformed roots and shoots, particularlywhen treated with auxins. This cut-piece method offers the potential toincrease the availability of plantingmaterial from a limited number ofpropagules.

While it seems that the presenceof the radicle has an inhibitory effecton shoot formation when applyingthis cut-piece method, the results arepromising. Ohnishi, Komiyama (1998)estimated that by using >3 cm seg-ments, a 1.5-2-fold increase in avail-able planting material can beobtained for Kandelia candel. Thisapproach also seems to have sub-stantial potential for species witheven longer propagules (e.g.Rhizophora mucronata with propag-ule lengths of 40-75 cm).

Tissue culture ormicropropagation

of mangroves

While considerable work hasbeen carried out on terrestrial plants,only very limited tissue culture exper-imentation has been undertaken withmangroves to date. Limited tissueculture work on the mangroveBruguiera gymnorhiza has been con-ducted by Satuwong et al. (1995).Progress in micropropagation of man-groves, including Avicennia marina,has been reported by Rao et al.(1998). Working with A. marina fromeastern Australia (photo 9), a tissueculture protocol has been establishedby Cousins, Saenger (in press).Despite these very limited studies,micropropagation is also a potentiallysignificant area for mangrovegermplasm improvement.

Nursery andplanting

techniques

Nursery and planting techniquesvary considerably among variousmangrove species. By way of exam-ple, a summary of the techniquesemployed for Avicennia spp. is givenbelow. Similar summaries for severalother important species are given inSaenger (2002).

The crypto-viviparous propagulesof Avicennia species are usually col-lected from around the base of mothertrees when they mature. When kept inair, these propagules lose their viabilitywithin a few days. They may be directlyplanted into sheltered areas by “dib-bling”—where the propagule is gentlypushed into the soft sediment untilfirmly wedged. “Dibbling” is usuallyundertaken during neap tide periodsto allow the seedling to develop roots.Pre-treatment of propagules has some-times been used to decrease the estab-lishment time. Such treatment consistsof placing propagules in small nets andexposing them to daily tidal inundation


DOSSIER

Photo 9. Micropropagation of Avicenniamarina: these plantlets werevegetatively propagated in half-strength MS medium through threegenerations in aseptic culture. Photo P. Saenger.

to hasten decay of the pericarp.Removal of the pericarp by pre-treat-ment reduces the establishment timeto 2-3 days, compared to 5-6 dayswithout pre-treatment. Alternately,propagules may be raised in nurserybeds that are exposed to daily tidalinundation. Seedlings are raised forabout 1-2 months after which they aregently pulled out of the ground andpacked for transport to prechosenafforestation sites where they are usu-ally planted out in 3 cm diameter holesat 1.0 x 1.0 m spacing.

Propagules for nursery raising aresimply placed on the surface of freelydraining sand and vermiculite mix-tures, kept in full sunlight and wateredonce daily, preferably using 25% sea-water which suppresses fungal infec-tions in the seedlings and acclimatesthem to the saline conditions that willprevail after they are planted. Forexample, growth and survival rates aresignificantly higher for Avicenniamarina in 25% seawater than in fresh-water. Humid conditions and the singleaddition of a slow-release fertilizersuch as “Osmocote” (NPK 18:2.6:10 atapproximately 3 g per 10 cm pot) willenhance and ensure optimal growth.

Site-speciesmatching

From studies of their naturaloccurrences, some insight has beengained into the soil conditions underwhich specific mangroves performoptimally. Site selection is of primaryimportance at the commencement ofany planting programme when themost favourable sites should be theinitial target. Detailed surveys shouldbe carried out to determine potentialplanting sites, followed by consulta-tion with other stakeholders toensure that there will be no interfer-ence with other valuable ecosystems,activities or conservation initiatives.

Site selection andcharacter ization

Site surveys should examine atleast the following parameters inassessing suitability: (1) Exposure:Mangrove seedlings will not survivein areas exposed to periodic highwave energy or persistent wind-gen-erated turbulence. Thus, sites shouldbe sheltered from wave energy in

semi-enclosed embayments orlagoons, or where shelter is providedby coastal features such as head-lands or offshore reefs and sand-banks. (2) Substrate stability: This isanother requirement for mangrovegrowth, at least during the establish-ment phase. Sheltered localities gen-erally exhibit stable substrates buttidal scour or littoral drift can occur insheltered locations and cause ero-sion or accretion of sediments. Suchareas are often easily recognized bytheir sedimentology (e.g. coarse grav-elly sediments, pronounced sand rip-ples, absence of crab burrows, etc.)and should be avoided. Where suchareas cannot be avoided, temporarystabilizing techniques (e.g. grassmatting, chicken wire, tyre barriers)may be necessary. (3) Shoreline mor-phology/sedimentology: Mangrovesgenerally grow best in muds andclays which have been depositedunder sheltered conditions and whichare regularly inundated by tidalwaters. Topographic positions foroptimal growth are generally in thetop third of the tidal range, and somerecontouring may be necessary toachieve this at any particular site.

Once a site has been selected,the site characteristics can beassessed to identify species bestsuited to the site. The degree ofwaterlogging (soil Eh), depth and fre-quency of tidal inundation, and pore-water salinity are probably the mainfactors determining species suitablity(figure 1). Conversely, if a plantationof a particular species is to be estab-lished, the requirements of thatspecies will govern plantation sitechoices.

Field tr ials

Field trials in which differentspecies are matched against differentedaphic conditions are essential priorto any planting programme. For exam-ple, Li et al. (1996) introducedBruguiera sexangula, Sonneratiacaseolaris and Rhizophora apiculatato Shenzen and North Bays (~22° N),Guangdong, from material collected



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ocarpusPteroro

Cladium LagunculariaRhizophora

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Osbornia

BruguieraHeritiera Lumnitzera

AegicerasRhizophora

Avicennia

Figure 1. The upper graph shows the distribution of dominant species against soil salinity (g L-1) andsoil Eh (mV) at 25 cm depth at Guadeloupe. The lower graph shows selected species againstsoil salinity (g L-1) and soil water content (% fresh weight) measured over 1.5 year atProserpine, Queensland. (After Saenger, 2002).

from Dongzhai Harbour (~20° N) onHainan Island in 1993. Three yearslater, both B. sexangula and S. caseo-laris were growing well (maximumheight of 1.5 and 3.0 m, respectively),while R. apiculata was unable to sur-vive at the more northerly site.Although it is tempting to suggestthat the colder conditions wereresponsible, the latitudinal change israther small and it seems likely thatcertain specific soil conditions suitedsome species but not others. Suchsite-specific characteristics can onlybe determined through field trials.

Silviculturalmanagement ofplanted areas

The major objectives for manag-ing any plantation or restored areashould be to facilitate natural regen-eration, to enhance productivitythrough fertilization and weed or her-bivore suppression, and to select tar-get areas where some assisted regen-eration is required. The selectiveintroduction of additional speciesmay also be considered either toincrease the biodiversity of the com-munity or to enhance the standingstock with suitable understoreyspecies.

Site management

Many mangrove plantations orrestored areas require stringent sitemanagement, including temporaryregulation of access to minimize dam-age to the area by human or animaltrampling, grazing, and trailbikes, etc.In addition, some form of temporaryshelter from current scouring may beneeded to assist in stabilizing thesediments after disturbance and toallow the seedlings to become estab-lished. Once the site has been re-sta-bilized after construction, or onceassisted regeneration has been car-ried out, the mangroves are likely torequire little in the way of on-goingmanagement.

Natural and assistedregeneration

Self-regeneration is an impor-tant aspect of a plantation or restora-tion project as costs of establishingplantations or maintaining restoredareas will vary significantly depend-ing on the extent of artificial plantingthat may be required.

Blanchard, Prado (1995) usedclearcut strips in Rhizophora mangleforests in Ecuador to study the factorsinvolved in determining natural levelsof regeneration. They concluded thatlarge trees produce more propagules,resulting in more being availablelocally for recruitment without anyinput from long-distance propaguledispersal (figure 2). Given the degreeof local recruitment, they suggestedthat a 20 m wide clearcut strip wouldallow for adequate regeneration inmost cases. On sites with less tidalinundation (<20 tides/month) orwhere bordering trees have a DBH<25 cm, well-shaped, reproductivelyactive seedling mother trees shouldbe left during felling.

Impediments to natural regener-ation include infestation of clearedareas by the mangrove fernAcrostichum. Natural regeneration ofplantations may also be affected by

fauna, i.e. quite apart from propagulepredation, grazing of establishedseedlings and saplings may be locallysignificant. In Bangladesh, for exam-ple, spotted deer (Axis axis) play asignificant role. Biotic interactionscan also affect the regenerationprocess. The climber, Derris trifoliata,may seriously affect growth and sur-vival in some areas, while insectinfestations have been reported tocause failures in recruitment inAvicennia germinans and Rhizophoramucronata plantations.

0

5 000

10 000

15 000

0-5 5-10 >10

Distance from seedling-mother-tree (m)

See

dlin

g d

ensi

ty (n

/ha)

Figure 2. Rhizophora mangle seedling density (number ha-1) in relation to distancefrom seedling mother trees in strip clearcuts in Ecuador. Vertical bars arestandard errors. (Data from Blanchard, Prado, 1995).

Photo 10. Monitoring the survival rates of Sonneratia apetalaplanted in different months. Bangladesh. Photo P. Saenger.


DOSSIER

If an assisted regeneration pro-gramme is required, the followingapproach is suggested: propagulesneed to be collected and eitherplanted out or raised in the nursery.For planting, propagules can be scat-tered over the target areas or alterna-tively pushed into the substrate. Thepropagules should be dispersedwhen the area is not expected to beflooded for a few days, thereby allow-ing them to become firmly estab-lished prior to subsequent inunda-tion. Some losses can be expectedand it is important to ensure that dis-tribution of propagules to the site isrepeated as necessary. If losses arehigh, propagules may need to be heldin place temporarily using chickenwire, seagrass matting, etc. In somesituations, there is greater survivaland growth of propagules if they arenursery grown before planting out.This allows seedlings to develophealthy root systems before implan-tation. Propagule extablishment suc-cess rates are clearly site specific butwere found to range from 30-90%.Nursery-grown seedlings generallyshow higher success rates thanpropagules. Planting out of seed-lings should be done at the mostfavourable growth period, i.e. mid-summer, to ensure maximal survival.At other seasons, a decline of 10-20%in seedling survival can be expected.

Cost of assistedregeneration

Costs for any of the describedapproaches are difficult to quantify.The cost of restoration of mangroveareas is highly variable, depending onfactors such as local labour costs, thesite characteristics (including itsaccessibility and size), its proximity topropagule sources, and whetherpropagules, seedlings, or transplantsare to be used. Examples fromAustralia and the USA are provided bySaenger (1996) and Snedaker, Biber

(1996), respectively.

Plantationperformance

Optimal planting season

In Bangladesh, planting fromJune to August appears to result inmaximum survival of newly plantedSonneratia apetala seedlings(figure 3, photo 10). Not only the timeof planting, however, but the age ofseedlings is a contributing factor, andseedlings older than 12 months gen-erally have low survival rates. In someareas such as the Chittagong andNoakhali Divisions, winter planting isconsidered to result in higher survivalrates but, to date, no experimentaldata support this view.

Optimal init ial spacing

A wide range of plant spacingshave been used in mangrove plantingprogrammes. Determining properspacing should be based on minimiz-ing competition (photo 11). Thinningwill occur naturally, and artificial thin-ning can be delayed to later vegeta-tion development stages by properspacing. For Avicennia marina, 1.5 mspacing was used at the Brisbane air-port site (Saenger, 1996); after4 years no evidence of self-thinningwas apparent.

Photo 11. A four-year-old plantation of Avicennia marina for landscape beautification in Dubai, United Arab Emirates. Photo P. Saenger.

A M J J A S O N D J F M A M J J A S O N D J F M-20

0

20

40

60

80

100

ObservedCalculated

Months

Sur

viva

l (%

)

Survival 6 months after planting

Figure 3. Percent survival of Sonneratia apetala seedlings 6 months after planting out from thesame nursery stock over a 24-month period. Both the seasonal changes in survival andthe declining trend due to increasing age of seedlings can be recognized in the fittedcurve (r2 = 0.7, p <0.001). (Data from Islam et al., 1992).




DOSSIER

The growth performance ofSonneratia apetala planted at variousdensities is given in table III. For timberproduction without thinning, an initialspacing of 1.2 m appears to be optimal.For coastal protection, however, wherefeatures such as multiple stems orreduced height are desirable, initialspacings in excess of 2 m might bemore suitable.

Where thinning products aretapped for economic benefit (e.g. char-coal production in Matang MangroveReserve), higher initial planting densi-ties are generally used. Where thinningproducts have little or no economicvalue, it is preferable to adjust initialspacing to reduce the need for thinningand to optimize plant growth.

Survival

Because of the highly dynamicnature of the Bangladesh coastline,the survival of mangroves is generallypoor and replacement planting isoften required for up to 3 years. Insheltered localities, however, survivalis generally around 70%. Long-termsurvival is also highly variable, butsurvival in 5-year old Sonneratiaapetala ranged from 29-52% in exper-imental plots at Barisal (table III).

Assessment of standingstock

The general assessment ofstanding stock or biomass is similarin plantations and old-growth man-groves, and many techniques devel-oped for natural mangrove areas canbe directly applied to the evaluationof planted mangroves. Biomass esti-mation methods fall into three broadbut overlapping categories: clear-felling, representative tree sampling,and the establishment of allometricrelationships.

Clear-felling involves harvestingof the entire above-ground biomass(AGB) from a specified area. The plantmaterial is usually sorted into the com-ponent parts (wood, branches, leaves,fruits, and flowers) within the individ-ual species constituting the stand. The

weight of each component and thesummed total are converted into dryweight values per unit area. Examplesof the use of this approach for man-grove old-growth forests include Lugo,

Snedaker (1974) and Christensen

(1978), while its applicability to man-grove plantations was demonstratedby Aksornkoae (1975). While efficientin young and small-sized stands, theclear-felling method becomes more dif-ficult to use for biomass estimation asthe stand or tree size increases.

Representative tree sampling isparticularly suitable where stands areeven-aged or have an obvious seriesof ages. Under such conditions, suit-able representative trees can beselected for felling and harvesting ofthe individual components. The dryweights obtained per tree are thenmultiplied by the stand density (treesha-1) to estimate the stand biomass(Choudhuri, 1991).

Allometric techniques have beenwidely used to estimate stand bio-mass in terrestrial forests (Brown etal., 1989). Such methods involveestablishing a relationship betweenthe biomass of whole trees, or theircomponent parts, and some readilymeasured parameter such as diame-ter of the stem at breast height (DBH),and/or height of the tree (H). Once theallometric relationships have beenestablished, the technique can beapplied in a non-destructive way atother sites; in contrast, the other twotechniques are site-specific and likely

to introduce considerable error whenapplied at other localities. Allometricrelationships between AGB and DBH(and/or H) have been reported for arange of mangrove species, includingthose of high forestry interest.

The general question of the relia-bility of allometric relationships forestimating biomass and their applica-tion to forests of similar species in arange of environmental settings hasbeen widely considered (Brown et al.,1989; Henry, Aarssen, 1999). Wheresampling takes place from relativelydense, closed-canopy forests, treeshape may be influenced by neighboureffects such as self-thinning of lowerbranches. Similarly, the crown propor-tion may differ between dense andmore open forests where crown expan-sion is less restricted. Thus, a crowdedtree would be expected to have asmaller DBH and crown than an open-grown tree of the same height (H).

The appropriateness of statisti-cal techniques used to derive allo-metric relationships is theoretically ofgreater importance. For example, allallometric relationships for man-groves (as for most forest systems)have been derived by least-squaresregressions, where either DBH (andH) or AGB must be selected as anindependent variable and regressedagainst the other. The use of reducedmajor axis regression, which does notassume that either axis is fixed, ismore appropriate than least-squaresregression (McArdle, 1988).

Table III. Mean survival (±SE), height and diameter at breast height (DBH), stemwoodproduction and tree quality at different initial spacings for 5-year-old Sonneratiaapetala plantations at Barisal, Bangladesh, from three replicated random blocks.(Data from Saenger, Siddiqi, 1993).

Spacing Survival Height DBH Stemwood Unforkedproduction trees

(m) (%) (m) (cm) (m3 ha-1 y-1) (%)

0.85 x 0.85 29±14 9.1±0.8 8.8±1.3 16.1±2.3 90±7

1.2 x 1.2 52±9 8.7±0.3 7.9±0.3 18.5±2.7 90±2

1.7 x 1.7 42±15 8.9±0.2 9.7±0.5 11.8±2.2 84±2

2.4 x 2.4 37±21 7.8±0.5 13.6±2.5 5.6±1.2 73±6

3.4 x 3.4 39±21 7.9±0.8 12.5±3.1 2.0±1.0 38±16

Despite the practical and theo-retical shortcomings of allometricrelationships, they nevertheless pro-vide useful and consistent results;internal consistency can be evaluatedfor any given species by summing theestimates of biomass for individualcomponents (derived from their allo-metric relationships) at a particularDBH, and comparing this value withthe estimate obtained for total AGB atthe same DBH. As Clough, Scott

(1989) showed, the independent esti-mates for total AGB thus obtained

were within 10% for most speciesover the size-classes sampled.

Selected allometric equations formajor species for AGB or other compo-nents (in g dry wt.) in relation to DBH(cm) for individual trees are providedin table IV. These include significantallometric relationships for the majorOld and New World mangrove species.Allometric equations for a similarrange of species in relation to bothDBH (cm) and H (m), or leaf area (m2),are provided in Saenger (2002).

Mean annual increment

Assessing the performance ofany plantation depends largely on theobjectives of the planting exercise,and monitoring parameters need tobe selected accordingly. Generally,however, assessment is usually doneannually by monitoring the survivalrate and one or more structural char-acteristics of the stand, generallyincluding DBH and H, although otherparameters such as basal area (BA),diameter other than at breast height(D), above-ground biomass (AGB),and timber volume (V) are commonlyused in forest inventories. For exam-ple, in an ecological restoration atLaguna de Balandra, Baja CaliforniaSur, Mexico, the following parameterswere deemed to provide an assess-ment of performance (Toledo et al.,2001): survival rates of plantlets atweekly, monthly and then 6-monthlyintervals for 4 years, together withdata on height increments and num-ber of leaves per plant.

Measuring the increasing AGBwith variously aged mangrove planta-tions is time-consuming and merelyprovides pseudo-time-series, althoughallowing some comparison betweenthe performance of a particular planta-tion against other plantations or old-growth mangroves in the same region.Data on AGB from variously aged plan-tations can be divided by the age ofplantations to provide a time-averagedincrease or mean annual increment(MAI) in AGB. As shown in figure 4,these MAIs range from 3.2 t ha-1 y-1 for5-year old plantations to 17.1 t ha-1 y-1

in 15-year old plantations in Malaysia.Although these time-averaged

increases in AGB are useful, there arechanges in the MAI over the age of astand, with an initial increase up toaround 15-20 years followed by adecline as the stand matures andwhen biomass accumulation decrea-ses on a yearly basis (figure 4). Thus,measuring MAI at shorter intervalswill more accurately reflect the cur-rent annual increment (CAI) of thestand at any particular time. Whilethe terms MAI (mean growth rate to



Table IV. Allometric equations for various mangroves and their component parts based ondiameter at breast height (DBH). (After Saenger, 2002).

Species & component Equation Regression coefficient

Avicennia germinansAbove-ground biomass AGB = 140.0DBH2.4 r2 = 0.97, n = 25

Above-ground biomass AGB = 94.2DBH2.54 r2 = 0.99, n = 21

Trunk biomass TB = 9.79DBH3.20 r2 = 0.97, n = 21

Branch biomass BB = 392.6DBH1.44 r2 = 0.94, n = 21

Leaf biomass LB = 23.6DBH1.82 r2 = 0.95, n = 21

Laguncularia racemosaAbove-ground biomass AGB = 102.3DBH2.5 r2 = 0.97, n = 70

Above-ground biomass AGB = 208.8DBH2.24 r2 = 0.99, n= 17




Rhizophora mangleAbove-ground biomass AGB = 177.9DBH2.47 r2 = 0.98, n = 17





Proproot biomass PB = 12.62DBH2.97 r2 = 0.97, n = 17

Rhizophora spp.Above-ground biomass AGB = 128.2DBH2.6 r2 = 0.92, n = 9

Above-ground biomass AGB = 105.0DBH2.6848 r2 = 0.99, n = 23

Bruguiera gymnorhizaAbove-ground biomass AGB = 185.8DBH2.3055 r2 = 0.99, n = 17

Bruguiera parvifloraAbove-ground biomass AGB = 167.9DBH2.4167 r2 = 0.99, n = 16

Ceriops australisAbove-ground biomass AGB = 188.5DBH2.3379 r2 = 0.99, n = 26

Xylocarpus granatumAbove-ground biomass AGB = 82.3DBH2.5883 r2 = 0.99, n = 15

Note: Biomass of all components is measured in grams dry weight for an individual tree. Diameter at breast height (DBH) is in cm.

any age) and CAI (instantaneousgrowth rate at any age) measuregrowth rates, CAI should be used forshorter assessment intervals whenthe actual (presently occurring) incre-ments in AGB (or any other character-istic) are being measured.

As for AGB, MAI can also be cal-culated for any other parameters,such as DBH, BA or H, resulting inDBHMAI, BAMAI or HMAI. Thesemeasurements are commonly usedfor rapid assessment as they are rela-tively easy to obtain.

In plantations where timber pro-duction is an objective, measurementof timber volumes in permanent plotsis used to monitor stands (Saenger,

Siddiqi, 1993; Devoe, Cole, 1998).Such detailed forest inventories arecostly and time-consuming and rarelycarried out on an annual basis.Rather, they are performed at longerintervals and the changes in volumebetween successive surveys expres-sed as mean (or current) annual incre-ments in volume (VMAI or VCAI in m3

ha-1 y-1).Volumes (or standing stock) of

mangrove stands are generallyderived from permanent plots usingallometric equations, and expressedas m3 ha-1. Relatively few data areavailable on volume standing stockand even fewer on volume or otherincrements (VMAI, DBHMAI, HMAI);some of these have been collated inSaenger (2002).

Rotation and thinningschedules

Determining rotation times andthinning schedules requires somedata on growth rates (as VMAI) andstanding stock (as V), as well as theeffect of natural thinning in the standor plantation. More importantly, themain products to be obtained fromthe stand (e.g. fuelwood, fence posts,poles, piles, sawn timber, pulp chips,charcoal) will determine the rotationtime in a commercial operation. Someexamples of various rotation timesare summarized in table V.

In Bangladesh, thinning is gen-erally not required because of the rel-atively slow rate of tree growth, thelow returns from the thinning prod-ucts, and the loss of trees in planta-tions due to stem borer attack.However, in some dense Sonneratiaand Avicennia plantations, thinning iscarried out after 9-10 years when upto 50% of the stems may be removed(Saenger, Siddiqi, 1993). Thinning ofthese plantations consists mainly ofremoving stunted trees and cuttingsmaller stems from multi-stemmedtrees.


DOSSIER

Table V. Rotations (in years) for various mangrove forestry products. (After Saenger, 2002).

Country Fuelwood Poles Sawn timber PulpFence posts Pilings chipsCharcoal(10 cm DBH) (25 cm DBH) (40 cm DBH)

Bangladesh 15-20 20

Fiji 15-25 40 40

Gambia 30 30 30

India 15-20

Indonesia 20-35 20

Malaysia 15-30 15-30 20-25

Micronesia 25-50 70-100 100-140

Myanmar 295

Philippines 7-15

Puerto Rico 30

Thailand 15-30 15-30

Venezuela 15-30 30 30

Vietnam 20

Virgin Islands 25

0.0

5.0

10.0

15.0

20.0

0 5 10 15 20 25 30

Age

y = -0.041x2 + 1.342x + 1.101

r2 = 0.356

AG

B M

AI

Figure 4. Changes in mean annual increment of the above-ground biomass AGB MAI(in t ha-1 y-1) with age of variously aged mangrove plantations in Indonesia,Malaysia and Thailand. (After Saenger, 2002).

Indices of “health”in mangrovecommunities

Apart from monitoring the struc-tural development of old-growth orplantation mangroves as a measure ofgrowth performance, it is also useful toassess the “health” of the trees, standsor forests. Such assessments are com-monly made on the basis of indicatorsthat have been found to occur undercertain pathological conditions orother forms of environmental stress.

A preliminary list of such indicesof mangrove “health” (table VI) hasbeen compiled from observations onAvicennia and Rhizophora (Saenger,2002). Although this listing is tenta-tive, it is intended to provide an easyand rapid means of assessing a man-grove stand in terms of the presenceor absence of certain characteristicssymptomatic of pathological or otherstressful conditions. In this sense,this list may be used as an early diag-nostic tool.

Conclusions

Modern perceptions of man-groves comprise a complex system ofeconomic, usefulness (or functional),intrinsic, and symbolic values. A greatvariety of motives therefore currentlyunderpin mangrove planting activitiesthroughout the world. As has beenillustrated, these range from purelycommercial motives such as thereplenishment of mangrove forests fortimber production, to solely aestheticones, such as the beautification ofdegraded coasts. In between, theenhancement of biodiversity is assum-ing greater significance. Whatever theobjectives of planting mangroves, andthese may be multiple, the applicationof forestry principles to all phases ofthe planting programme, from designthrough execution to evaluation, willpromote the achievement of theseobjectives. Given the rapid rate of man-grove loss around the world, the devel-opment of effective replanting tech-niques and procedures will becomeincreasingly important in the future.



Table VI. Indices of “health” in mangrove trees, stands and forests: “healthy”communities will not display these features. (After Saenger, 2002).

Aerial rootsproliferation of undersized prop roots

twisting and curling of pneumatophores

adventitious aerial roots

death of prop root tips

fissuring or peeling of periderm

Trunks and branchestop-dying of uppermost and outermost sun branches

fissuring and cracking of bark

expanded and/or more numerous lenticels

shortened internode distances

cessation of terminal shoot growth

appearance of trunk sprouts from secondary meristems

Foliagereduced leaf number per branch

reduced leaf size, twisting and curling

abscission of buds and immature leaves

altered leaf maturation sequence

spotty chlorosis or necrosis

change in leafing and shedding processes

reduced leaf area index

Reproductive structureschange in timing of flowering and fruit set

absent or grossly excessive flowering

deformed seeds and propagules

development failure of fruit

excessive abortion of immature fruit

Regenerationfailure to orient geotropically

seeds and propagules fail to establish primary root system

abnormal growth forms in established seedlings

failure to initiate primary branching

chlorosis or necrosis of propagules

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DOSSIER

References

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