unesco - rain forest regeneration and management

8/7/2019 UNESCO - Rain forest regeneration and management

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IUBS Unesco IWB

RAIN FORESTREGENERATION AND MANAGEM ENT

Edited byMALCOLM HADLEY

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RAlN FOREST REGENERATIONAND MANAGEMENT

REPOK OF A WORKSHOP

Guri, Venezuela24 - 28 November 1986

Unesco-Man and Biosphere(MAB) ProgrammeUnited Nations Environment Programme (UNEP)International Union of Biologicai Sciences (IUBS)Institut0 Venezolano de Investigaciones Cientificas(IVV?C)CVG Electrificacion del Carod, CA (EDELCA)

Edited byMalcolm HadleyDivision of Ecologicai SciencesUnesco7, place de Fontenoy75700 Paris. France

SPEQAL ISSUE- 8BIOLQGY INIERNATiONAL

THE INIERNATiONAL UNION OF BIOUXICAL !SCENCESNEWS MAGAZiNE


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PREFACE

In early November 1986, Venezuela opened the most recent phase of the Guri dam projecta t the time the world's largest hydroelectric complex, having a capacity of 10,300 megawattswith a reservoir covering an area almost twice the size of Luxembourg. Sorne two weeksaf te r the formal opening of the dam, Guri was the venue for an international workshop onrain forest regeneration and management.Plans for the Guri workshop were elaborated by a smaii working party organized by ArturoGomez-Pompa at Harvard Forest in July 1985. This working party was, in turn, convenedin the light of a recommendation by the International Coordinating Council for the Manand Biosphere (MAB) Programme of Unesco, a t it s eighth session in December 1984, th atrain forest regeneration might provide a suitable focus for future comparative work on tropicalecology within the framework of MAB.Hosted by the state hydroelectric Company CVG Electrificacion del Caroni, CA (EDELCA),the Guri workshop was organized from 24-28 November 1986 as a joint venture by the Manand Biosphere (MAB) Programme of Unesco, the Decade of the Tropics of the Internat ionalUnion of Biologicai Sciences (IUBS), the United Nations Environnent Programme (UNEP)and the Instituto Venezolano de Investigaciones Cientificas (IVIC). Additional technical andfinancial inputs were provided by the Food and Agriculture Organization (FAO), the WorldResources Institute and the Commonwealth Science Council. Participants included some20 research workers and forest managers from Venezuela together with some 40 invitedspecialists from 20 other countries and international organizations. The list of participantsis given as Annex 1.The workshop was concerned with the interface between research and management andwas aimed at exploring the implications t o management of present scientif ic knowledgeon rain forest regeneration. In addition to producing a synthesis of sc ientific informationon rain forest regeneration, subsidiary aims were to identify gaps in information andunderstanding, in respect t o both scientific hypotheses and the needs of management, andto explore directions for future collaborative research and action. The intention was notto prepare an encyclopedic or comprehensive li ter atu re review. Rather, th e workshop wasconcerned with the review of se lected technical issues and ecological processes within thecontext of management. The motivation was to help bridge the gap between the sciencesassociated with the wet tropics and on-the-ground management.The workshop was based on the presentation and discussion of thematic reviews, complementedby case studies (see Annex 2). Synthesis reviews dealt with such topics as sylvigenesis andarchitec tura i diversity, regeneration dynamics a t various spatial scales, physiology offastgrowing species, reproductive biology and genetics, fru it and seedling ecology, nutrientcycling, Current management programmes. Case studies dealt with research and managementexperience in particuiar locations and regions. A dual challenge to those presenting casestudies was to inform a wider audience of t he experience gathered in a particular projector technical field, but also to suggest what might be the wider practical applications ofthe case study for rain forest management. Links between science and technology betweenresearch and resource use - came within.the ambit of the reviews and case studies. Thebroader economic and societal context of rain forest regeneration and management wasnot within the direct te rms of reference of the workshop. Not tha t issues like'land tenure,economic .evaluation of forestry schemes, international trade , etc., are not important. Theinverse.is true - their importance is overriding. But such an objective and focus would havecalied for a completely d ifferent type of workshop agenda and participants' list. Though


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CONTENTS

PrefaceContentsList of figures, tables, boxes, plates

1. Setting the scene: trends in tropical land use

2. What the manager needs to know

3. Ecological processes and rain forest regenerationThe tropical forest environmentForest dynamics and questions of scaleTree characteristics, sylvigenesis and architectural diversityReproductive biology and genetics of tropical forest trees3.5 Tropical forest seed ecology

3.6 Nutrient cycling processes3.7 Research sit es and case studies

4. Issues in moist forest management, land use and silviculture4.1 Current programmes in tropical land use and forest management4.2 On costs, benefits and economics4.3 Social context

5. Concliisions and recommendations

References cited

Annex 1. List of participants

Annex 2. Papers presented at the workshop


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Page1

LIST OF FIGURES, TABLES, BOXES, PLATESThe humid tropics: a changing world (Plat e)Deforestation of closed tropical forests, and new plantations (Figure 1)Largest national areas of productive closed broad-leaved forest (Table 1)Tropical Forest Resources Assessment (1990) (Box)What a manager of t ropical rain fo rest needs to know (Figure 2)Two illustrat ions of response surfaces (Figure 3)Relating ecological research and different management needs (Figure 4)Character syndromes of the two contrasting ecological classes of t re especies - pioneer and primary (Table 2)Relationship between gap size and the relative contribution of variousguilds to gap fiiiing (Figure 5)River dynamics, rain forest regeneration and species diversity (Box)Integration levels in fo rest archite cture research (Figure 6)Diagrammatic representation of two regeneration stra teg ies (Figure 7)Diagnostic characters and characteristics of trees with different speciesstra tegie s (Table 3)Reproductive biology and genetics of tropical forest t rees (Table 4)Towards a functionai classification of fores t systems at Sierra del RosarioBiosphere Reserve in Cuba (Box)Seed germination in tropical forests (Table 5 )The tropical forest 8s a chemical factoryEcological research on rain forest regeneration at a sampling of sitesin the humid tropics (Table 6)Plots for studyiag run-off and erosion in French Guyana (Plate)Demographic studies a t Pasoh, Malaysia (Box)Large scaie experimentai plots and silvicultural treatments in the Cted'Ivoire (Box)Celos Silvicuitural System (Box)Larg esca ie forest transformation - the Ja ri project (Box)Logging by machines (Box)Revamping shifting agriculture in northeastern India (Box)Tropical fores t development within an incentive- perspective (Table 7)Dry evergreen forest a t Sakaerat, Thailand (Plate)


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1. SE'TNG THE SCENE: T R E N ~ SN TROPICAL LAND USE

A nurnber of recent initiatives have served to focus world attent ion on tropical forestecosystems and their resources. They include the Tropical Forestry Action Plan coordinatedby FA0 (FA0 1986, 1987), the World Resources Ins tituters Caii for Action on Tropical Forests(WRI 1985), the Dutch Tropenbos programme (Tropenbos 1986, van Beusekom e t al. 1987a,1987b), etc. These reports provide a rich source of information on status and trends in tropicalforest land use, updating and complimenting earlier state-of-knowledge reports such as thatprepared a decade ego by Unesco, UNEP and FA0 (Unesco 1978). Among the items ofbackground information that can be drawn from these several reports, together with theintroductory overview of the Guri workshop (Gomez-Pompa and Burley, in press), are thefoilowing:Forests cover more that 4000 million hectares, or one-third of the earth's land surface.Of the total fores t area , about 42% is found in the developed countries (almost alitempera te) and 58% in the developing countries (mostly tropical).

The humid tropics: a changing world

The humid tmoics - a region unknown t o many, with many unknowns t o science, duRng a periodof rapid, far-reaching change. One of 36 coloured posters (120 x 80 cm) from the Ecologyin Action exhibit, produced by Unesco in 1981.


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Tropical fores t s can be d iv ided in to two main types : c losed fores t , where the t reesan d u n d erg ro wt h co m b i n e t o co v er t h e g ro un d , a s i n t h e c l o s ed h um id fo res t s fo u ndin high-rainfal i regions of the Am azon Basin and the is lands of South East Asia;and open form at ions wi t ti cont ir iuous grass cover , such a s the open savanna woodlandfound rnain ly in Afr ica . In addi t ion , the re a re o th er typ es of fore s t s , including bamboowh ich , a l t h o u g h n o t s t r i c t l y a t r ee , i s an i m p o r t an t fo res t r e s o u rce in m an y t ro p i ca lzones , and mangroves , a key e le me nt in mar ine food chains , which can be impor tan tsources of wood for fuel and building rnaterials .Fo res t s provide en ergy (half the wor ld l s populat ion depen ds on fuelwood) , indus t r ia lwood products (20% of which corne f rorn developing count r ies ) , food , fodder ,phar rnace ut ical p roducts , and o the r non-wood products such as f ibres , rubber , gumsand res ins . For es t s ar e a l so a pr iceless ecological resource , p r o tect in g land andwa ter resources , cont ro l l ing f loods , ward ing off wind eros ion , s tor ing and cycl ingnut r ie n t s , and provid ing ha bi ta t s for wi ld l ife . They con s t i tu te a r i ch s toc k of valuableg en e t i c r e s o u rces, an d m ay h av e an i m p o r t an t ro l e i n m ed i a ti n g ch an g es in g l o b a lc l imate .Es t i rnates of ra t es of for es t convers ion have been the bas i s of cont inuing cont roversy ,caused in par t by d i f feren t def in i t ions . Thus , Myerl s (1980) s tudy , p repa red underthe aspices of the U S Acaderny of Sciences , was concerned main ly wi th thet ransfo rma t ion of t rop ic al rno is t fore s t s f rorn a "primaryl1 s ta ge t o var ioushuman -impacted categor ies , and wi th the resu l t ing l ikely impac t on b io logicald ivers i ty and spe cies surv ival. The FAO IUNEP assessment , on the o th er hand , wasbased on th e convers ion of for es t to non-fores ted land (FAOIUNEP 1981, Lanly1982) . Comp ar i sons of th e resu l t s of t he tw o types of survey have been m ade byMolofsky e t al. (1986), arnong other s .Acco rdi n g t o t h e F AO/ UNEP c r i t e r i a , 7.5 mil l ion hectares of c losed fores t and 3.8m i ll io n h ec t a res o f o p en fo res t a r e c l ea red each y ea r in t h e t ro p i cs (F i g u re l), nt o t a l an a re a a lm o s t eq u i v a l en t t o t h a t o f J av a . Th e u n d er ly i n g cau s es o f

F i g u re 1. Defo res t a t i o n o f cl& tropicai f o r e s t s and new tropical planta t ions , From F A 0@987), a f t e r F A O /U N E P 0981)Deforestation of closed tropical forests(million hectares) Productive forests[7Non-productive forests

.4frica Latin hmeri ca Asia1976-80 1 3 3 - 1 4 . 1 2 1 1 . 8 2

1.26 07 3. 1 O7 1.; 0.12

1981-851.26 0.07 1.67 O. 15

New tropical plantations(million hectares) 0 low-growing hardwoodFasr-growing hardwoodm ofnvoodAfrica Latin America Asia

~ 4 0 . 4 ~2.05

1976-80O. 17 O. l 5 O. 15 0.29 1.07 0.6 9

cEzZa.63 0.96 0.51 *'"~ 0 " " 2

2.67 2.191981-85

0.23 0.25 O. 14 0.25 1.56 0.36 0.45 1.18 0.16


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deforestation and forest degraaation are poverty, inequitable land distribution, lowagricultural productivity, poor land-use policies, inappropr iate development (includingprojects outside the fo res try sectorl, weak institutions and rapid population growth.In spite of these high rat es of deforestat ion, t her e are 36 countries with at leastone million hec tar es of tropical forest, suitable for productive management,represent ing more than 90% of the world total (Table 1).

Table 1. Lag est national areas of productive closed broad-leaved fores tl.Estimated for 1985 (x 106 ha). From Schmidt (in press)

Country ~ o t a l ~ Logged Countryover ~ o t a l ~oggedover

BrazilZaireIndonesiaPeruIndiaColornbiaBurmaGabonVenezuelaBoliviaCameroonMalaysiaPapua New GuineaCongoGuyanaSurinameMexicoEcuador

French GuyanaPhilippinesMadagascarKampucheaVietnamCentral African Rep.NicaraguaThai landPanamaLaosAngo 1aParaguayGuatemalaCte d'IvoireNigeriaond duras^

GhanaSri Lanka

1) Definitions: "Productive closed bmadleaved for est s ... cover ... a high proportionof the ground and do not . have a continuous dense grass layer ... theircharacteristics ... allow (or might allow) for the production of wood for industryf!"Logged over one or more times during trie las t 60 to 80 yearsfr., From: FAO/UNEP(1 981).

2) The forest is not al1 lowland tropical in al1 cases. For example, in the BrazilianAmazon the estimate for tropical forest is (x 106 ha): 185.9 dense forest ; 10.0dryland forest; 76.6 open forest; 42.3 tmnsit ional and seasonal formations (tot al314.8).3) .Revised from FAO/UNEP 1981 based on personal communication (1987) from

T. W. W. Wood to R. Schmidt.


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The re ar e thre e main poss ib i l it i es for us ing ra in fores t s . F i rs t , i s convers ion ofspecies - r ich for es t s in to s impl i f i ed , species -poor sys tem s of var ious k inds , sucha s p lan ta t ions , croplands , e tc . Second, i s the re te n t ion of mixed fores t s , wi th theex t r a c t i o n o f s o m e o f t h e i r p ro d u c t s b u t w i t h t h e m a i n fu n c t i o n a l ch a r ac t e r i s t i c smain ta ined . Thi rd , is the to t a l p reservat ion of samples of "naturai" ecosys tems .Th es e t h re e u s es can b e s een a s co m p l em en t a ry , ch o i ce d ep en d in g o n t h e i n t r in s i cch a ra c t e r i s t i c s o f a p a r t i cu l a r s y s t em . Un fo r t u n a te l y , t h es e t h re e pr i nc i p alp o s si b il it ie s a r e t o o o f t en v i ewed as co m p e t i t i v e an d o p p os in g. Proponents of onep o s si b il it y a r e o f t en n o t i n t e res t ed i n t h e o t h e r t wo , an d i n s t i t u t io n s an d p ro fes si o n al sco n ce rn ed wi t h t ro p i ca l fo res t s d i v i d e a l l t o o f r eq u en t l y a l o n g we l l d em arca t edl ines of op in ion , in t ere s t and ideology. In Mexico , for exam ple , the f i r s t g roup i sdominated by econornis t s and agronomis t s , the second by fores ters , the th i rd byb io lo g is ts . Th e r e s u l t o f t h es e d i f f e r i n g p e rcep t i o n s i s t h a t t h e g ro u p wi th t h e g rea t e s teco nom ic inf luen ce on deci s ion-makers holds the g re ate s t sway, and th i s has beenth e f i rs t rnent ioned group.Th e m a i n o b s t ac l e s t o t h e s u s t a i n ed m an ag em en t o f t h e r e s o u rces of t ro p i ca l fo res t ss eem t o l i e i n t h e l a ck o f p o l i c it a l co m m i t m en t an d f of f i n an c i a l an d i n s t i t u t i o n a ls u p po r t. A t t h e s am e t i m e , s c i en t i f i c r e s ea rch h as a co n t r i b u ti o n t o m ak e in he lp in gthe pol icy-maker and man ager in thei r t ask .

Ropical Forest ResourcesAs s es s m en t (1990)F ro m 1 9 7 8 t o 1 9 8 1 , a global survey the ye ar 2000. The assess rnent forof th e wor ld 's t rop ica l for es t s and 1990 wi l i l argely fo llow th e methodologywoodlands was carr ied o ut by F A 0 developed in the previous survey , wi thand U N E P . Th e as s es s m en t co v ered s o m e n ew fea t u re s i nc lu d in g : a s s es s m en t76 t ropica l coun t r ies and provided of to ta l wood volume; in tegr at iona s e t o f q u an t i t a t i v e e s t i rn a t e s i n o f a s s es s m en t o f t ro p i ca l an d n on -a s t an d ard fo r m a t o n t h e s i t u a t i o n t ro p i ca l zo n es; u p d a ti n g o f v eg e t a t i o nan d t r en d s a t t h a t t irn e. Th e r e s u l t s m ap s, t h e i r co m p u t e r i za t i o n an do f t h e s t u d y d id rnu ch t o r a i s e t h e i n t eg ra t i o n w i t h o t h e r u s e fu l d a t aaw aren ess of deci s ion-makers and and maps ; s tudy of envi ronrnentala ler t in g publ ic op in ion t o th e ser iousness impl icat ion of defores ta t ion and for es to f t h e p ro b lem o f d e fo res t a t i o n an d d eg rad a t io n i n t h e t ro p ics ; an do f i t s h a rm fu l co n s eq u en ces fo r t h e d i s s em in a t i o n of t h e m e t h od o lo g yenvi ronrnent and socio-economic to developing count r ies .development of t rop ical count r ies .I t a l s o s e rv ed as a bas i s fo r the A two-s tep approach wi ll be fo llowed.formulat ion by F A 0 of the Tropical In the f i rs t s t ep , a l1 ex i s t ing informat ionF o res t ry Ac t i o n P l an, s u b s eq u en tl y ( r ep o r t s , m ap s, e t c . ) fo r t h e co u n t r i e sadop ted by the in terna t ional cornrnunity concerned wi ll be co l lected . Wherea s a f r a rn ewo rk fo r h a r rn o n iz i n g an d ex i s ti n g d a t a a r e n o t r e l iab l e ,s t reng thenin g coop erat ion in suppor t in terp reta t ion wi l l be made of sa te l l i t eo f n a t i o n a l e f f o r t s t o f i g h t d e fo res t a t i o n . i m ag er i e s fo r o b t a i n in g an u p - to -da tearea of the var ious vegeta t ion c lasses .Ten y ea r s h av e e l ap s ed s i n ce t h e f i r s t In a s eco n d s t ag e , a l l a r e a an d gro win gsurvey was in i t i a ted , and F A 0 i s now s tock f igures wi ll be ad jus ted t o aplanning a new Tropical Fore s t cornmon ref ere nc e da te , namely 1990.Resources Assessrnent . The pro jec t This wi ll make the da ta compa rablea i m s t o a s s es s t h e f o res t r e s o u rces a t r eg i o n a l an d g lo bt il l eve l s. Es t i m a t esof the t ropic al coun t r ies by end 1990, wi l then be made of the pas t ra tet o e s t i m a t e ch an g es t h a t h av e t ak en o f ch an g es d u r in g t h e p e r io d 1 98 0 -place s ince 1980, and to bui ld a l t e rna t ive 90 and of the pro jected changes dur ingscena r ios abou t for es t changes by 1990-2000.


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2. WHAT THE MANAGER NEEDS TO KNOW J. Palmer

The objectives of a management agency, a t a given time and phase, wiil determine its needsfor information. I t may be difficuit for managers to articulate their information needs,sometimes because they may find it embarrassing to explain or defend the current practicesof their governments in respect to forest management, in other cases because there is a lackof clear policy in respect t o management or time might just not be available for putting existingtools and approaches into use.One such approach is through decision charts and checklists, which are useful for trainingforest managers and have been produced by Colyear Dawkins,for Ghana and Uganda, by FrankWadsworth for Puerto Rico and extended to the rest of the neotropics, and by John Palmerfor the Unesco/UNEP/FAO State-of-knowledge Report on tropical forest ecosystems (Unesco1978). The charts a re useful also t o managers for explaining their needs and time scales topoliticians and to Ministries of Finance. One highly simplified chart on what a manager oftropical rain forest needs to know, in approximately chronological sequence, is shown as Figure2 . For simplicity the chart is confined to a primary management object ive, the productionof valuable timber on a large scale (tens of thousands of hecta res) to feed a capital-intensiveforest industry. The sheer size of areas under the control of a tropical silviculturist or afprest manager forces acceptance of a high level of heterogeneity in their forests, augmentedby the effects of logging operations. This difference in scaie surely accounts for much ofthe 'difference in approach to problems between the tropical rain forest manager and theecologist. The chart is limited further to the permanent forest estate, that is, the forestwhich is reserved legaliy for the supply of fores t products to fulfiii the nationai domestic(and perhaps export) requirements, in accordance with the nationai forest policy.The concern here is not with forestry for the recovery of water catchments uaiiiaged throughimproper land use, nor with the management of forest s scheduled for conversion to otherforms of land use on the basis of land capability surveys and subsequent zonification. Noris the concern with the management of smaU communal or privately owned woodlots, whichar e leqitimate a reas of interes t in considering the issue of tropical rain forest management,but would require separate and somewh8.t different treatment.Ten principal steps are identified in the decision-chart presented here, which deals with anobjective comnion to large areas of tropical rain fores t - that of producing valuable timberon a large scaie within a capital-intensive fores t industry.

1. National forest policy: dic tates the broad outlines of work for the national forest service.2. LegisLative framework: places the forest service and forest operations in their legalcontext. Unfortunately the fores t law is too often set aside by short term considerationsof political and persona1 pecuniary advantage (= bribery and corruption).3. Land tenure: the forest service may find it hard to determine the true traditionalrightholders or land owners (especiaiiy in the southwest Pacifie), or there may be no simpleanswer, or there may be politicai interference with the operatiion of the statute law on landtenure. Note that difficulties caused to the forest manager on this and the two ?reviouspoints are often due to the deliberate setting aside of the law by politicians.4. Specific object ives of management: these shouid take into account the historical demandson the forest, and the commitments to supply local consumers as weii as large industries.The objectives ar e not se t on a once-for-aiways basis but should be kept under review. Formai


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Figure 2. What a manager of tropical rain forest needs to knowParagraphnurnber(see text)

1. National forest policyIt2. Legislation frameworkIt3. Land tenure14. Specific objectives of management for this forest1

10. Long-terrn studies on dynarnics:(e.g.1- pollinators/dispersers/predators,their interactions with crop tree

species and each other- regeneration banks iseed, seedlings,saplings)- growth and yield models, based onyield plots, inventories and DS

st ati c inventory.

a . Proper ties

6c: Possibilities ofsecondaryprocessing,singlespecies ormixtures

7. Dynarnics of desirable species'l. Short-term studies on dynarnics:- ecological tolerances- responses to silviculturaltreatment- logging darnage to t ree s and soi1(Note that paragraphs 5 to 10 should feed back to 4)

6

and uses ofdesirablespecies

Routinediagnosticsarnpling

7

7(need forma1 experirnents to aid the 6b- PrOpertiesdevelopment of response surfaces) juvenile woodof crop treespecies


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fore stry Working Plans usually requ ire a quinquennial or decen nial revision. Th ere shouldbe f e e dba c k f r om t he suc c e e d ing s t e ps i n t he de c i s ion c ha r t t o e nsur e t ha t ob j e c t i ve s a r eadjus ted t o cope wi th long- te rm mark e t chan ges and wi th i rnprovements to the knowledgebase for s i lvicul ture and management . The objec t ives may imply la rge-sca le and year -roundope ration s, or small-scele and perhap s seaso nal operations; or a combination. For exarnple,a la rg e fo res t indust ry might re rnove the big logs with heavy machinery and a second s tagel icence might p ermi t loc a l people to remov e res idues for f i rewood and to col lec t minor fores tproducts.

5. St a t i c inventory: this i s poss ibly th e f ie ld in which sc ient i f ic knowledge has had th egr e a t e s t im pa c t , s i nc e e l e c t r on i c c or npu te r s t ook the d r udge r y ou t o f s a m ple c a l c u l a t i onsand da ta sor t ing and tabula t ing. Inventor ies a re now mul t ipurpose, to sui t mul t iple objec tives ,bu t j us t a s t he r e ha s to be a pr imary ob jec t ive so ther e must be a pr i rnary sui te of var iablesto be es t imate d, which de te rm ines the sampl ing scheme. Sub-sampl ing examines regenera t ion.Nowadays tha t wouid include th e seed bank in th e soi l , and here i t i s perhaps sa lutory to recordtha t s i lvicul tur is t s were s tudying the soi l seed banks before univers i ty ecologis ts becameenthused by th e subjec t .6. Assess pr ope r t i e s and uses: t he p r ope r t i e s a nd use s o f m a tur e t r e e s o f spe c i e s f oundby th e inventory to be ava i lable in com merc ia l qua nt i t ies should be reviewed or researched.Note tha t in a l l , or a lmost all, t ropic a l countr ies the number of spec ies tes ted and found tobe indust r ia lly sui tab le by fores t products lab ora tor ie s exceed s th e number of spec ies ac tua l lym a r ke t e d f r om t r op i c a l r a in f o r e s t. T he d i f f e r e nc e i s pa r t l y a r e f l e c ti on o f t he s t rong lyconserva t ive marke t ing of t he t im ber t r ad e and par t ly an indica t ion of the pressure whichth e fores t indust r ies business can br ing to bear on the re levant minis ter . Subsequent s tudies(6b) examine t he p rope r t ies of juveni le wood of th e second crop spec ies , to se e if an ear lyharv est would provide technica i iy adequa te t imber ; more advanced s tudies (6c) look intothe poss ibi li t ies of m ixing spec ies in a s ingle processed product , such a s chipboard or paper ,as wel l as methods of adding va lue by secondary process ing ( such as over laying pr inted f i lmsand plas t ics on t0 plywood, o r se l l ing furni ture m ade f rom mixed spec ies ins tead of only f inetimbers) .7. Dynam ic inventory: s tudy should co nce nt ra te on the popula tion dynamics of the des i rablespec ies . These a re d ef ined pr imar i ly on t i ie bas is of t im ber prop er t ies and secondar i ly onobserved ecology (growth habi t , posi t ion in re la t ion t o th e canopy in approp r ia te se ra1 phasesa f t e r logg ing , g r ow th r a t e ).8. Diagno st ic sampl ing: DS i s a genera l ized and improved form of t he var ious l inear sampl ingmeth ods developed in Malaya, Nigeria, Sabah, Sarawak and Uganda. As the nam e implies,i t is used t o de te rm ine t he app ropr ia te type of s i lvicul tura l t r e a tm en t (i f any) . The re i s nowmore e rnphasis on ear ly ident i f ica t ion of potent ia l f ina l c rop t rees ( "Leading Desi rables t ! )an d a concent ra t ion on the i r l ibera t ion f rom compet i t ion. In many t ropica l countr ies thereis a more or less expl ic i t land pol icy of l'Use i t o r lose i t" , s o there i s s t rong pressure for af o r e s t s e r v i c e to re -establ ish i t s c la im to manage th e fore s t a f te r a logging opera t ion. Anear ly s i lvicul tura l t r ea tment , not necessar i ly poison-gi rdl ing of undesi rable spec ies , i s thusof te n pol i t ica i iy des irable . However th e fores t se rvice needs to e s t a b li sh t he sc i e n t i f i c w or thof t he t r e a tm e nt s a ppl i ed a f t e r be s t- guess i n t e r p r e t a t i ons of t he D S.9. Shor t - te rm studies on dynamior : as in DS t he e m pha s i s i s on t nose de s i r a h l e spe c i e s( d ef in e d a t s t e p 7 ) a nd c ons ide r e d toge the r as a c rop, ra ther than on the individua l spec ies .T hr e e c l a s se s o f s t ud i e s are espec ia i ly indica ted by for es t managers :- ecologica l tole rances , de te rm ined by sample surveys in space and t ime as weii asby f o r m a l e xpe r im e nts ;- r e sponse to s i l v ic u l tu ra l t r e a tm e nt s ( se e s t e p 8 above), inc luding response t o th e majorinte rv ent ion which i s usua lly th e logging opera t ion i t se l f . Fa i lure to quant i fy thepre- and post -logging Sta tes of the fores t before the appl ica t ion of exper imen ta ls i l v ic x l tu ra l t r e a t m e nt s ha s r e su l t e d i n a r e g r e t t a b ly l a r ge num be r o f un in t e r p re t a b l eexper iments . The di f f icul ty exper ienced by many fores t se rvic es in es tabl ishing a rdmainta ining s i lvicul tura l t r ia l s in t ropica l ra in fores ts i s perhaps re f lec ted in there


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being re la t ively few publ ished cas e s tudies repor t ing such expe r iments (se e howeverboxes on the work in C te d ' Ivoi re and Sur iname la t er in th i s repor t ) ;- e f fe c t o f a c t ua l and s i m u l a t ed l ogg ing dam age t o s t and ing t r e es and t o t he s o i l;

The em phas i s should be f i rmly on exper im ents ra th er tha n on observat ion . Hypothes i s t es t ingis rare ly necessary , i t i s the quant i f i cat ion of th e response which i s needed. Resul t s of thet r ia l s should be incorporated in to growth models (based main ly on y ie ld p lo ts , se e s te p 1 0 )whose s ens i ti v i ty i s o f t en de t e rm i ned by t he q ua l i t y l quan t i t y o f da t a a t t he ex t r e rne t i e s ofth e site/silviculture/growth response surface (F igure 3) . Such convent ional t r i a l s providejust th at f ramew ork sugg es ted in Car1 Jordan 's rev iew of nut r ie n t cycl ing processes (see a l soSect ion 3. 6 of t he p res en t r epo r t ).10. Long-terrn studies on dynarnics: t hes e a r e i n t ended t o p rov ide t he bu lk o f t he d a t aneeded fo r growth model i ing and y ie ld con t ro l sys tems . The main dat a source should be awel i -s tra t if i ed and regular ly remea sured sys tem of y ie ld p lo t s, supplem ented by occas ional

F i gu re 3. Two illustrations of response surfac es shown as t h r e e d i m e n s i o n a l graphs

R e s p o n s e s a x i s ,s u c h a s i n c r e m e n t(m m d i a m e t e r l y r )

R e s p o n s e a x i s ,such a s numbero f t r e e s p e rh e c t a r e


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inventories to improve spat ial coverage, and making provision for incorporation of routineDS results. The high ra te of turnover which is now known to apply to natural fores t previouslythought to be very stable applies also to Leading Desirables (LDsj. This makes modellingdiff icult if not impossible from data collected only frorn LDs. I t would seem that there isno satisfactory alternative to recording data from yield plots for ail stems of desirable species,over a defined minimum size. Much more effort needs to be invested in growth studies andmodelling, since the failure to make secure predictions of future yield makes forest servicesvulnerable to arbi trary poli tical decisions concerning logging operations. Three classes ofstudies from those summarized in the workshop review papers and in Section 3 of this report,would be particularly helpful to forest managers:- critical conditions for pollinators/dispersers/predators of the crop tre e species, their

interactions with the trees, as weli as with each other.- dynamics of the regeneration banks (seed, seedlings, saplings/poles).- the ecology of climbers (lianes, trepaderos), particular ly those of silvicul tural importance

such as Merrernia in Southeast Asia and the southwest Pacific and Acacia ataxacanthain west Africa.

Some managers would add a requirement for studies on nut rient cycling. However, since4 m3 ha-l yr-l is about the best commercial growth ra te t ha t could be obtained in lowlandtropical rain fore st, and since 10 m3 ha-l yr-l seems to be about the r ate above which someartifical fertilization would be necessary to sustain yields, nutrient studies are not high inthis particular listing of priorities.Routine diagnostic samplings may indicate that some areas of forest have less than theminimum number of potential crop trees in the regeneration. Depending on how the crit ica lstocking levels are set in the DS interpretation instructions, the prescription may be to enrichthe forest with line plantings or to replace it entirely with artificial plantations. The lat terrnay also be prescribed if demographic pressure or market demand increase so much tha tthe naturai fores t must give way to a more directly productive form of land use. Suchconversion is not necessarily an indication of manageriai failure: the forest may have beendamaged by natu rai or human forces before i t passed to the control of the forest service,or the demand may exceed the biological capacity of the natural fores t to produce the desiredmateriais.Departures from the managerial process outlined above are caused by social, economic andpolitical pressures. Plantation forestry has suffered as much as tropical rain forest frombudget fa ilures and land tenure problems: maybe more, because plantation forestry is themanagement of intentionaiiy unstable systems and requires timely interventions to preventthe collapse of the system.In summary, although ecological knowledge implicitly underpins forest management, in anexplicit forrn i t is only one of a number of factors influencing the management of tropicalrain forest. Ecologists might have more influence if they interpreted their research in termsof potential impact on management, while managers should art icu late their research needsmore clearly and phase them into gra nt si ze d projects as understood by ecologists. The landmanager should be able to indicate his research needs for any one land management systemin any one area of ecologicai research, a s suggested by the matrix shown in Figure 4. Suchapproaches would facilitate collaboration between forester and scientist in tackling particularmanagement problems.


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Figure 4. Relating ecologica l research and different management needs in the humid tropics

Securi tyof landtenure

poor

LandManagementSystema

1 w r high

Demographic pressure


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3. ECOLOGICAL PR OCESSES AN D RAIN FOR EST REGENERATION

3.1 THE TROPICAL FOREST ENVIRONMENT F.A. B a z z a zLight, temperature, moisture, nutrients and herbivory ar e among the factors af fecting plantgermination, photosynthesis and growth, that need to be considered as part of the environmentalsetting within which rain forest regeneration takes place.The Light and temperature environmentThe upper canopy of the forest in wet tropical regions receives less radiant energy than thecanopy of other tropical forests because water molecules in the humid air absorb this energy.Much attenuation occurs as the light passes through the vegetation; the amount of radiantenergy available near the forest floor can be extremely low. The slope of the light attenuationcurve varies greatly and is determined by leaf area density and leaf absorbance characteristics.The strata that affect vertical light distribution are more recognizable in forests dominatedby one or @ few species. Another aspect of the forest's light environment is the shift in spectralquality as the light passes throueh the canopy. The foliage absorbs red over far red light,so the light near the forest floor has littl e red wavelength light.The substantial three-dimensional variation in the light environment is largely due to thedistribution of the vegetation. Because of sunflecks, a shoot or a single leaf may experiencerapid shifts from very low to very high light levels. This af fects carbon-gain capabilities,and the growth and resource allocation of seedlings. Sunflecks are an important part of thelight environment and carbon gain of understory plants, and rapid response of photosynthesisto sunflecks may be important for them.The light environment dictates the temperature of air, plants, and soil in tropical forests.Although the temperature of emergents and outer par ts of the fores t canopy may rise duringmidday, there are no detai led or accurate measurements of this rise. In the understory, dailyvariation in leaf temperatures may be s m d and leaf and air temperatures remain close exceptduring sunflecks.Soi1 temperature may differ little from air temperature in the understory but may be muchhigher than air temperature in gaps and clearings. The differences are most pronounced nearthe soil surface, where the germination and early seedling growth usually occurs. It isimportant to recognize that. plants as individuals may experience much variation in the levelsof resources as they grow from smail seedlings to mature, reproducing individuals, and thatpar ts of the same individual may simultaneously experience different environments.A t the level of the leaf, vert ical microclimatic gradients govern, t o a large extent, the energybalance of individual leaves and their carbon-gain capacities . Though leaf energy balancemeasurements for tropical trees are very limited, studies suggest that there may be nofundamental differences in energy balance between tropical and temperate forest trees.In the forest , both Sun and shade leaves may be found on the same individual. Their carbon-gaincapacities and contribution to the to tal carbon budget of that individual ar e probably different.Furthermore, within a species, shade-grown seedlings generally have lower light saturatedphotosynthetic rates than do sun-grown seedlings, though there are exceptions. This is alsotrue for leaves on the same individual. Recent data also confirm previous conclusions thatunderstory species have lower photosxnthetic rates than do primary canopy species and thosein turn have lower rate s than pioneers. These trends in photosynthesis are similar to those


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in temperate forests and the rates are not very different between these two systerns.Water economyLandsberg's (1984) theore tical analysis of the water econorny of tropical rain forest s showedthat when the canopy is thoroughly wet, significant stemflow can be expected and the soila t the base of large emergent and canopy trees rnay become considerably we tte r than theres t of the forest. This might contribute t o spat ial heterogeneity of resources in the forest.Evapotranspiration from the canopy rnay be large and is driven by the energy balance of thecanopy, resistances to water flow, and soil moisture levels. Incoming radiation and the albedoare the rnost important controllers of evaporation; the lat te r is high in clearings with exposedsoil surfaces or dry vegetation, lower in gaps, and lowest in intact forest.Energy in the forest canopy is dissipated by evapotranspiration, latent heat tr ansfer, andsensible heat transfer, which includes advection and convection. Low evaporation from soiland low air rnixing in dense tropical forests lead to high relative humidity, which in turn reducesevapotranspiration. Of course, the amount and distribution of rainfall may Vary considerablyamong locations. This affects forest dynamics by changing the rnorphology, physiology, andbehaviour of forest organisrns. In gaps and large clearings, rela tive air humidity may be lowand may limit the establishment and growth of some forest species. However, soil moisturecontent rnay be high in these locations. Patterns of rainfall are likely to interact with foreststructure and dynarnics to generate complex patterns of water econorny for differentindividuals, and there is evidence that in some pIaces tropical trees may experience severewater stress, which may not be comparable to water stress observed in temperate forests.NutrientsReviewing lite rat ure on nut rien t dynarnics in 62 tropical forests , Vitousek (1984) concludedthat , in general, lowland tropical forests have more nitrogen and a lower dry mass to nitrogenratio in litterfaii thaq do rnost temperate forests. Phosphorus return, however, is very low.Vitousek cciicluded that usualy phosphorus, but not nitrogen, is lirniting in these systerns.Plants growing in dif ferent soils in Arnazonia have diffe rent concentrations of nitrogen,phosphorus, calcium, and rnagnesium concentrations and different nutrient-use efficiencies(Cuevas and Medina 1986). Different vegetation types in a given area may be limited bydifferent elements. In Arnazonia, Tirra Firme is phosphorus lirnited, Caatinga is nitrogenlimited, while Bana appears to be lirnited by both nitrogen and phosphorus. Cuevas and Medinarelated differences in the degree of sclerophylly and leaf duration arnong these three vegetationtypes to nutrient availbbility. The issue of nutrient cycling is further discussed in Section3.6 of the present report (pages 33-35).GrowthBecause of the length of the growing season, rnost tropical tre es grow faster (especially aboveground) than do temper ate deciduous trees. It is also weii established that pioneer speciesgrow fas ter than do climax forest species. Reports of extrernely fas t growth of pioneer speciesar e common. Growth has been measured rnost cornmonly as height extension because of theease and non-destructive nature of the rneasurements. Height growth rat es of over 2 rn yr-

have been recorded for sorne tropical trees. Girth growth has aiso .been recorded for alarge nurnber of species.The range of possibilities fo r timing growth is best viewed as a spectrum frorn continuousgrowth to annuai rhythrnic growth. Annuai growth rings ar e uncornrnon in most tropical trees.On the other hand, sorne species do have clear zonations of wood tha t resernble annual ringsbut are not necessarily the result of annual growth.In a comprehensive long-terrn study of growth of 46 cornrnon spec ies in a Costa Rican tropicalforest, Lieberrnan et al. (1985) have reported that : (a) shade-intolerant canopy and sub-canopyspecies have maximum growth rates and are short-lived; (b) shade-tolerant sub-canopy tre eslive about twice as long as understory tre es and graw a t approxirnately the same maximumrate ; (c) canopy and sub-canopy trees th at are shade tolerant but respond opportunisticallyto inciieased light levels have long life spans and high maximum growth rates; and (dl understory


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species have slow maximum growth rates and short life spans.HerbivoryHerbivores rnay sometimes play an important role in forest regeneration through the rernovalof photosynthetic and support tissue. This may result in changes in architecture and, in ext remecases, the death of individuals. Herbivory may indirectly increase rnortality by providingentry for pathogens. Insects seem to be the most important herbivores in tropical forests.SIassive defoliation does occur, but more commonly parts of leaves or of individual plantsare consurned. The average value of leaf area consumed by herbivores in many tropical forestsseerns to be between 10 and 20%. The rernoval of tissue a t the seedling stage is especialiycrucial.The contribution a damaged leaf makes to th e carbon economy of the plant depends on whenin its life-span th2 leaf was damaged. There is good evidence tha t young leaves are rnoresusceptible to herbivory than old leaves and in some fores ts leaves of pioneers ar e nioresusceptible than climax species. Removal of seed tissue by herbivores may be even morecrit ical for the fate of the resulting seedlings.

3. 2 FOREST DYNAMICS AN D QUESTIONS OF SCALE T.C. WhitmorePrimeval tropical rain fores t, undisturbed and stable since the dawn of time, is a myth. Rather,tropical forests are in a continual sta te of flux, changing a l l the time. Instability occurs onseveral time-scales.In secular terms, the cl imate of the humid trcpics has fluctuated throughout the Quaternaryand probably the Ter tiary too, and various lines of evidence show that tropical rain fores tshave expanded and contracted as climate has fluctuated. Today, their natural extent is ator near the maximum ever achieved.At the other end of the temporal scale lies dynamic change due to the growth and death ofthe trees of the forest. The forest canopy is a mosaic of gaps, patches of juvenile t ree s growingup in former gaps, and mature forest. We may recognize a fores t growth cycle of gap, buildingand mature phases. What grows up in a canopy gap determines the composition of the fores tfor a long time, usuaiiy at least decades and sometimes centuries. Hence, the establishmentof building-phase forest is in some respect s the most important part of the growth cycle. Acrude distinction may be drawn between forest regeneration on smaii and large surfaces,in smaii and large gaps respectively, with recruitment from various sources of propagulesvarying in respect to gap size and severity of disturbance (Bazzaz in press; Figure 5) . Theseedling bank is most important in smaii gaps, while seed banks become more important inlarger gaps.In a canopy gap crea ted by the dea th of one or a few trees, seedlings already present in theundergrowth a re 'released' and grow up into building-phase forest. In a big gap by contrast(a gap created by multiple windthrow, landslide, vulcanism, cyclone, etc.), pre-existingseedlings die, there is a major shift in microclimate near and below the ground and this maysometimes cause death (though we lack hard evidence), otherwise physicai disruption does.Whatever the cause of death, the gap is filied by new seedlings which were not present belowthe previous canopy.Thus we have two sort s of tr ee species, those with shade-bearing (or shade-tolerant) seedlingsand those with light-demanding (or shade-intolerant) seedlings. The la tt er cannot regenerateunder any shade, including their own. These two species classes a re often known also as climaxor primary and pioneer or secondary species respectively, referring to their abilities toperpetuate in situ or not. Many other prcperties are linked to these seedling characterist ics,to form two contrasting syndromes (Table 2).If the return-time of large-gap creation is longer than the life-span of the pioneer trees thenas these die, smaii gaps will form in the forest canopy and climax species wili invade in .asecond growth cycle. This is secondary succession, which is defined as a directional shift


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T a b l e 2. C h a r a c t e r s y n d r o m e s o f t h e t w o c o n t r a s t in g e c o lo g ic a l classes o f t r e e s p e ci e s -p i o n e e r an d p r i m ary . F r o m Wh i t m o r e ( in p r e s s )P i o n e e r species P r i m a r y species

Sy n o n y m s s h ad e i n t o l e r an t s , l i g h t- s h ad e t o l e r an t s , s h ad e -d em an d e r s , n o m ad s , p i o n ee r s, b ea r e r s , d r y ad s , c l i m azsec ond ary spp . spp . , p r ima ry spp .S e e d

Disper sa l

D o r m a n c y

co p io u s , s m a l l , p r o d u ced l e s s co p io u s , l a r g e , p r o d u cedco n t i n u a l l y o r co n t i n uo u s l y an n u a l ly o r l e s s t h an an n u a l lyw i nd o r an i m a l s , f o r d i v e r s e , i n c l u di n g g r av i t y ,c o n s i d er a b l e d i s t a n c e s s o m e t i m e s o n ly l o c a lo f t e n ( ?a l w ay s ) p r e s en t ;n e v e r ( ? ) r e c a l c i t r a n t o f t e n a b s e n t ; o f t e n r e c a l c i t r a n t

Soi 1 s ee d b an k l p r e s en t ab s en t (? a l w ay s )H e i g h t g r o w t h f a s t s l o w e rWood u s u a i iy p a l e , l o w d en s i t y , o f t e n d a r k , h i gh d en s i t y ,n o t s i l ic e o u s s o m e t i m e s s i l ic e o u s

i n d e t e r m i n a t e , n o r e s t i n g d e t e r m i n a t e , w i t h r e s t i n gb u d s ( v i z s y l l ep t i c ) buds (v iz p ro lep t ic)~ o r k i r . ~ 3 high low

s h o rt - li v ed, o n e g en e r a t i o n long- l ived , seve ra l gen era t ion sp r e s en t , v i z h i gh tm o v e r p r e s en t , v i z s l ow t u r n o v e r~ o o t s 4 s up er fi ci al s o m e d ee pR o o t / s h o o t r a t i o 2 r 4 l o w h i ghPh o t o s y n t h es i s r a t e5 h i gh l o wT o x i c c h e m i c a k 6 l o w h ig hL ea f s u s cep t i b i l i t y h i ght o p r e d a t io n 7 low

G e o g r a p h ic a l r a n g e w i d e o f t e n n a r r owPh en o t y p e h i g hp l a s t i c i t y 8

low

1. Wh itmore (1983) 5. Ko yam a (19781, Ob erb aue r & Strain (1984)2. Boojh & Ram akr ishn an (1982) 6. s p ecu l a t i v e , ev i d en ce s l i g h t an d eq u i v o ca l3. Whitney (1976) 7. C ol ey (1983)4. Shukla & Ram akr ishn an (1984) 8. Baker (1965)


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Figure 5. Relationship between gap size and the relative contribution of various guilds togap filling. increased severity of disturbance dilring gap creation moves the timeaxis to t h e right. B = branches, AR = advance regeneration, S = sprouts. FromBazzaz (1984)

Gap Size ---+Severity of Disturbanced

with tirne in floristic composition. The pioneer species may be short-or long-lived, and thesegrow to be srnall and large t rees respectively.The forest which first colon!zes big gaps is known as secondary, and throughout the tropicsit consists of s tands of only one or a few species per hectare, in contrast t o most climax forestswhich have numerous species. Moreover, the total pioneer tr ee flora is everywhere smaiiwith sorne of it s species very widespread. There a re fewer pioneers in America and Africathan in Asia, where in Macaranga alone there are over 100 pioneer species.Eventuaiiy, probably usualiy after several centuries, there wiii no longer be a directionalchange in floristics; composition a t a given spot wiil change from one tree generation to thenext but overall a steady-state will have been achieved. This is the climax forest in whichcyclic replacement occurs of climax species of similar ecology. In some forests this conditionrnay never be reached because the return-tirne of cataclysms is too short.In recent years, there has been growing awareness of the importance of cataclysmic eventsand other large scale processes in shaping the regeneration of rain forests. At leas t four groupsof phenomena can be recognized:. Cyclones are a powerful factor in affecting forest growth, especialiy in the neotropics.. Fire has been shown to be a widespread and long-dated phenomenon in several partsof the tropics; examples include the extensive fires in East Kalimantan th at followeddrought in 1982-83, and the repeated fires that have occurred in southern Venezuelanrain forest during the past six milienia (Sanford et. al. 1985).. River dynarnics are an important factor affecting forest regeneration in areas such asWestern Amazonia (see box "River dynamics, rain forest regeneration and speciesdiversity").. Plate tectonics is ~no ther nechanism which has been shown to have important implicationsto rain forest dynamics in the western Amazonia, through the ef fect of Sub-Andeantectonics on fluvial perturbance (Rasanen et al. 1987). The suggestion is that the westernArnazonia is a fluviodynamic rnosaic and that the river dynarnics have affected the biotasince the early Tertiary.


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River dynamics, rain forest regeneration and species diversity

Recent research has suggested thatlateral erosion and channel changesof meandering rivers may be animportant cause of large-scale naturalforest disturbance and primarysuccession in lowland rain forests.Work in the upper Amazon region(Salo 1987, Salo e t al. 1986, Saloand Kaliiola in press) has indicatedthat primary succession on newlydeposited riverine soils is a majormode of forest regeneration. Theriver dynamics modify large areasbecause of the flat general topography,their high load of suspended solidsand the easily erodable ailuvialsubstrate.Landsat imagery analyses show that26.6% of the modern lowland foresthas characteristics of recent erosionaland depositional activity; 12.0%of the Peruvian lowlaiid fores t isin successional stages dong rivers,is under the influence of the modernerosion-deposition cycle. Thesefindings contrast with some traditionaiviews of Amazonian rain forest, whichhave tended to emphasize stability,with the dominant mode of forestregeneration occurring in light gapscreated by faiien trees.The research of Jukka Salo and hiscolleagues indicates that thoughmuch of the area of western Amazoniais covered with structuraiy moreor less monotypic forest, the forestis a mosaic of forest patches differentin their age, history and present dayenvironmental conditions. Modernrivers repeatedly disturb the areasformerly considered to be stablePleistocene refuges. The disturbancecreates habitat mosaics, and favoursthe maintenance of the high between-habitat ( P -type) species diversitycharacterizing the upper Amazon.This process may be viewed ascomplementary to or even replacingthe Pleistocene refugia hypothesisfor high species richness in this area.

Understanding of questions relatedto river dynamics is consideredimportant for the planning ofconservation policies in the region.Firstly, there is need for protectinglarge areas including whole catchmentareas (like the Manu national park).Secondly, protecting a stretch ofali rivers is the best guarantee forprotecting local floras and mechanismsfor forest regeneration.Reproduced here is a sideways-lookingairborne radar (SLAR) image of westernAmazonian forests (from Salo andKalio, in press, image courtesy ofONERN, Lima). It shows the f luvialregeneration cycle on present andformer floodplain generations incen tra l Ucayali floodplain a t Pucailpa,Peru. The forest regenerat ion cycleis initiated by lat era l channel erosionand subsequent sedimentation ofpoint-bars and migrating channelislands. The primary succession onthese deposits follows a sequentialpattern due to (i) further migrationof the channel, (ii) formation of agestuc tured sets of cohorts of the earlysuccessional trees according to theseasonal sediment accumulation and(iii) competition between species.The mosaic forest is formed on th9present floodplain generation composedof cut-off meanders (sequent ialsuccessional forests) and oxbow lakes.Transitional forests: with increasinaautogenic light-gap regenerationdominate the older floodplaingenerations outside the presentlyact ive meander plain. Finaliy thecoliuviai processes cause dissectionof the floodplain reliefs, resultingin the dominance of denuded forestbeds.In the accompanying figure, the relativewidth of the arrows indicates theareas most recently disturbed bythe channel erosion. These ar e theare as most likely to be re-disturbed.


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p+pquccessionalthe previous( nmdpivm 1

the dissecvdsurfaces


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3. 3 TREE CHARACTERISTICS, SYLVIGENESIS AND ARCHITECTURAL DIVERSITYR.A.A. Oldeman-J. van Dijk

Determination of the architectural diversity of tropical rain forest area s requires large-scaleas weU as smali-scale analyticai methods (Figure 6). Large-scaie analysis may entai1 theuse of sate ll ite imagery and aer ial photographs, which may show a given region with itsmountains, valleys, rivers and forest (A ) and at a more detailed scale, different forest typesand fornis of land use (B). More detailed surveys are needed to reveal the specific mosaiccharacter of a par ticular forest type (Cl,while a stil l more detailed level of investigation(D) is required for examining the s tructu re, processes and species composition of each kind

DEFORESTEDF O I E S I E D d,( \

C MATURE/ \DECAY ING

AERIAL LIMIT

Figure 6. Integrationlevels in forestarchi tecture research,from sirnplifiedsatellite i m a g e(A) to groundelevation of eco-unit (Dl. FromOldeman (1986).


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of fo rest patch or "eco-unit", an area on which forest s ~ a r t e do grow at the self-same moment(Oldeman 1983). At a s tiil smaller sca le, individual trees or par ts of trees can be analysed.Al1 of these methods rnay together be used in helping to diagnose the "status" and "valueMof a given area.Tree characteristics may provide complementary diagnostic characters, particularly whenconsidered in relation to crown character istics, lif e history types and regeneration strategies.Two contrasting regeneration s tra teg ies can be distinguished, which may be c d e d a "gamblerllor "struggler" str ategy (Bazzaz and Pickett 1980; Pickett 1983). Species with a garnblerstrategy produce large numbers of seedlings (Figure 7, Aa), which cannot survive in the shadedunderstory. Only those individuals survive that receive enough light from a canopy gap abovethem (Ab) . The few individuals that find a gap may grow very rapidly towards the canopy(Ac, Ad). The reproductive efforts are high, in order to increase the likelihood that at leastone individual juvenile wiil find a gap into which it may grow.Species with a struggler strategy produce smal numbers of very persistent juveniles (Ba)which may struggle but survive. They grow a lit tle and some even complete their li fe historywithin the densely shaded understory (Bb). When a gap is formed above a juvenile, growthis preponderantly horizontal rather than verticai, and the increased light levels may beaccompanied by maturation and reproduction (Bc, Bd). Eventuaiiy the canopy gap closesagain and the tre e resumes its struggler metabolism. The reproductive eff ort s of strugglersmay be much lower than for gamblers, because the life expectancy of each i~dividualuvenileis comparatively high.Combining regenerat ion str ategie s with Whitmorels (1975) lif e history types provides a morecomprehensive typology of the st rat egies that species may adopt to maintain themselvesin the forest. The foiiowing species str ategie s may be recognized using as examples informationobtained by Oldeman during work in the l at e 1960s in French Guyana.. Species requiring.no gaps: strugglers in extremo; adapted to continuously low light levelsthroughout the ir lives; crowns monolayered, more broad than deep; leaves borne onplagiotropic branches or branch-complexes or (in monocaul tr ees ) in a whorl a t the top ofthe stem. Growth may be preponderantly horizontal, even when a light gap is formed. InFrench Guyana, two groups can be distinguished; a fir st group of small monolayered tre es,mostly much smailer than 10 rn with large leaves, arranged in a single layer near or at thetop of the tre e, with minimal mutual shading of crowns; a second group of larger tr ees whichmay reach 10-15 m, morphologically more heterogeneous with a more complex archi tec ture.. Srnail gap specialkts: germination in the shade. Many large economicaily important trees(e.g. Malaysian dipterocarps) belong to this group. Includes both strugglers (e-g. slow-growing,shade-tolerant "heavy hardwoodsn such as Balau Shorea, Vatica, Hopea, often with plagiotropicbranches or branch - complexes and monolayered leaf arrangement) and gamblers (shadeintolerant, light hardwoods such as the Red Meranti Shorea, capable of very fas t growth ina high radiation environment, often with orthotropic branches and multilayered leafarrangements). In French Guyana, twelve examples of this group range from a pronouncedgambler to a pronounced struggler strategy.. Large gap specialists: germination in large gaps; gamblers in extremo, adapted tocontinuously high radiation levels; can only survive by outgrowing competitors. The weilknown archi tecture of th e pioneer t re e comprises a single leader, not (or sparsely) branched,with large leaves in a single layer a t the top. In French Guyana, two different growth stra teg iescan be recognized among the seven examples studied; fi rst , tha t of outgrowing competitorsby fas t height growth achieved at t he cost of building up a horizontally spreading crown (e.g.in Didymonpanax moroteni); second, tha t of building up a densely foliated, spreading,phyllomorphic crown that occupies space horizontaliy and that may outshade competitors(e.g. Amona paludosa, Apeiba burchelli).

It would seem that architectural features combined with crown characteristics mayreflect a treels environmental requirements and its capability to adjust to a changingenvironment. Common architecturai f eature s and crown characte rist ics of juvenile tre es


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Figure 7. Diagrammatic representa tion of two contrasting regeneration strategies. Undulatingarrows represent incident radiation: length of t he arrows indicates intensity. Seetex t for fur ther explanation. Afte r OIdeman and van Dijk (in press)

(8)STRUGCLER&!?&~ \TRATEGYLarge number Smali numberof non-per- of verysistent persistentjuveniles juveniles

pi, (a)1I

Only juveniles hlost juvenilesthat receive persist in thesome extra shade and(b) light may showsurvive some growth

Only one Growth ra tesjuvenile (horizontailysurvives, but + vertically)( c ) shows fas t increase upon

1growth gap formationk k l

1Surviving Growth ratesjuvenile decreasegrowth into when gap is

tthe gap closing. but

I towards the( d 1 canopy persist20


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Table 3. Diagnostic ch aracters and characteristics of tree s with differe nt speci es strategies. After Oldernan and van Dijk (in press)

Species requiring no gaps Small gap specialistscharacteristics Strugglers in extwmo Strugglers CambIers

Large gap specialistsGamblers in extrerno

ArchitectureOverall architecture Poor and simple Poor, simple to More complexmore complexOrientation Horizontal Horizontal to vertical Vertical

Poor, simple to more cornplex.Vertical, sometimes horizontal

Distribution of branches Unbranched or branches Diffusely branched or Branches in distinct tie rs Several possibilitiesne ar th et op branches near the topCommon architectura l Chamberlain, Corner, Troll, Roux Aubrville, Massart Several possibilitiesmodels RouxHeight growth Mono- or sympodial Mono- or sympodial Mostly monopedial Mostly monopedialBranch orientation Plagiotropic Plagiotropic Plagiotropic/Orthotropic Plagiotropic/OrthotropicBranching sequence Diffuse Diffuse Mostly interm itten t Diffuselintermitten tRamification branches Sparsely ramified Sparsely ramified Strongly ramified Sparsely to strongly ramifiedCrown characteristicsLeaf arrangement Very lit tle leaf surface, Leaves sparsely distrib- Leaves more or less dense- Several possibilitiesin a single layer a t the uted throughout the ly packed in several dis-

top C P O W ~ tinct layersLeaf size Large when unbra~ched , Small Small Often largesmall when branched

tu+


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may be used as diagnostic characters in helping to determine the status of a forest area (Table3) . When there is a prevalence of trees with a struggler strategy (species strategies 1 and2) ,' th e forest may be considered to be stable or mature, whereas a prevalence of gamblers(species strategies 3 and 4) points to a recently or frequently disturbed site. Evidence forsuch a correlation has been obtained in forested sites in Venezuela (van Dijk 1987), but morefield testing is required to confirm or refute its value.

3.4 REPRODUCTIVE BIOLOGY A ND GENETICS OF TROPICAL FOR EST TREES

Knowledge of reproductive biology and genet ic struc ture for tropical fores ts may be verylimited, but there is still information and experiences that can be shared and can be helpfulin deciding strategies for responsible fores t management. Below is reviewed the existingknowledge about such basic features as flowering and frui ting phenology, models of pollination,sexual systems, gene flow and genetic struc ture of populations, emphasizing the gaps in ourknowledge that are of cr itical importance in the management and conservation of tropicalrain forest trees. Summary recommendations on future research directions and on treeirnprovement programmes are also presented (Table 4).Flowering and fruiting phenologyFlowering. Tree species in a tropicsi rain forest display much variation in the timing, durationand frequency of flowering. Flowering may occur annuaily, supra-annuaily, or severai timesa year. In those species that flower more than once a year, quantita tive variation in theintensity of flowering among episodes has been documented. Species tha t bloom annuallymay also show variation in flowering and fruiting intensity between years.At the community level, flowering of related species is often sequential if the taxa a repollinated by the same guild of pollinators. Pollinators probably switch from one speciesto another as the floral resources of one species decline and tha t of the other increase.The temporal variation in flowering should be of considerable in terest to managers. Thenumber of seeds (and fruits) produced are often positively correlated with the number offlowers, but we do not know how the quantity influences the genetic quality of the seeds.The relationship between seed quanti ty and quality is of particular interest in species thatbloom supra-annuaily. Many species do produce a smali number of seeds in off years. Whetherthe quality of the seed is comparable to that produced in mast years is not known.The staggered blooming periods of related species also have management implications. Someof the sequentially blooming species may provide resources to the poiiinators a t crit ical timeswhen other food items are in short supply. If so, their removal from the community couldinfluence the pollinator guilds, and consequently, the plant guilds that depend upon thesepollinators.Fruiting. A s in the case of flowering, there is considerable variation among species withrespect t o timing, duration and frequency of fruiting. At the community level, fruiting inNeotropical rain forest s is strongly seasonal. For example, in both Panama and Peru, peaksin fruit production straddle t he star t and the l ate r part of the rainy season; i n between thefruit is scarce. When fruit is scarce , frugivores are believed to sustain themselves on a handfulof "keystonen plant species that provide nectar and fruits.At fir st glance, such community level pat terns may not be of much interest to a resourcemanager interested in a particular species, but the particular woody species may be dependentupon certain frugivores for seed dispersai. These frugivores in turn may rely on other speciesduring lean periods of f rui t abundance. The example also emphasizes the wide variety ofways in which the life cycle of a tropical fcvest t ree is linked with the ecology of other plant


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t

Table 4. Reproductive biology and genetics of tropical forest trees: fiverecommendations for future research, and five recommendationsconceming tree improvement programmes. After Bawa and Krugman(in press)

Recommendations for future research. Information about flowering and fruiting phenology, plant poilination interactions,sexual systems and mating systems at the level of communities and individualspecies is critical for success in management practices that impinge on variationin species composition. Such information is also vital for forest tree breedingprogrammes.. For conservation and long-term management purposes, it is imperative we beginto gather data on the spatial organization of genet ic variability at differentscales.. Given that genetic research is expensive and that tropical forests ar e diverse,it is suggested that a management approach incorporating genetic principlesbe focused on particular ecosystems or groups of species in a given geographicalarea.. Genetics work must be an integrai part of the overall management effort. Apartfrom forest tree breeding programmes, geneticists can contribute in many waysto the sustained management of natural forests and reforestation of degradedlands.. Geneticists working with tropical forest trees must shed the bias accrued through

experience with temperate zone conifers. The richness of biotic interactionsencountered by tropical forest t ree s is greater by several orders of magnitudes;consequently, the genetic outcornes are more complex and diverse.Recommendations concerning forest tree improvement programmes. The justification, technical direction, and resources committed to a tr eeimprovement effort must be closely related to the national or regional forestpolicy.. It should be clearly understood at the outset that a successful tree improvementprogramme is only one element of forest management and not isolated frommore traditional forestry activities.. Another criterion essential for a successful tree improvement activity is the

careful evaluation of technical skills available to implement an appropriate levelof activity.. Tree improvement programmes are of litt le value if the seeds and/or pollen cannotbe collected, stored, and grown in a nursery. A nursery operation needs to bea major element of the tree improvement programme. Without a successfulnursery programme, there is no way a tree improvement activity cRn succeed.. A tree improvement programme is only as good as the field tree plantingprogramme. Good professional plantation establishment and management areessentia l to the success and continued acceptance of improved materiai.


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and animal species in the community. This makes it d ifficult to design a sound managementstrategy on the basis of biological knowledge of the subject species alone.Poination modesThere is a tremendous diversity of pollination modes among trop ical rain forest trees. Thepollinators range from tiny wasps in the case of figs to large bats in the case of Cieba pentandmand other Bombacaceae.From the management perspective, pollination biology of individual species is of the greatestinterest . Yet, even for most prominent species, such informat ion is largely anecdotal, scantand incomplete. At the level of individual species it is particularly important to know theextent t o which the various species are dependent upon part icular pollinators. In cases ofextreme specialization, the management of the pollinator population becomes as importantas the management of the t re e species serviced by these pollinators. The degree ofspecialization may differ for part icular guilds of pollinators.An adequate management strategy must also take into account the way the populations ofpollinators might be influenced by changes in the frequency and composition of forest species.Tropical rain forests pose a tremendous challenge in this regard because, as mentioned earlier,groups of species often share the same pollen vectors. Because we know virtualiy nothingabout the phenology and population dynamics of the pollinators, we cannot assess the impactof changes in frequoncy of various plant species on the population of thei r pollinators.Sewal systemsThe diversity of pollination mechanisms in tropica l rain forest tr ees is matched by the diversityin sexual systems. Most species bear bisexuai flowers, but are self-incompatible. Many ar edioecious.In terms of management, the degree of inbreeding displayed by the individual is a cri tic alissue in assessing the gene tic quality of the seed crop. The amount of inbreeding is not onlydependent upon the genetic propensity towards selfing of an individual, but also on the spa tia lconfiguration of th e relatives. To the extent tha t the management involves alte ration ofdispersion patterns , the effec t of changing spa tia l patterns on the amount of inbreedingbecomes an important issue. In dioecious species, optimal spacing of male and fema le treesis an even more complex issue and cannot be ignored, especially in those cases where theproduct of economic interest is seed or fruit.Mating systems, pollen f low and effec tive population sizeA convenient way to esti mat e the amount of outcrossing (or inbreeding) is to anaiyze themating system by means of geneti c markers. The mating system is determined by the degreeof self-fertil ization, dispersion pat tern of related individuais (family struct ure ) and thecharacter istic s of pollen flow. The parameters th at determine mating system also definethe effective population size, which in essence describes the boundaries of geneticneighbourhoods within which the individuals m ate free ly with each other.Mating system has been so far quant itatively analyzed in two species of tropical rain fores ttrees: Berthollet ia excelsa (Brazil-nut) and Pithecellobium pedicellare, a mimosoid legume.The data indicate that the outcrossing rate in both species is very high, and that there isconsiderable variation among individuals in outcrossing rates. There ar e absolutely no dataon gene flow in tropical forest tree populations.From the management perspective, it is important to know the amount of inbreeding withina population and whether or not individuai trees significantly differ in outcrossing rates.Selective removal of trees can al te r the mating pat terns with unknown consequences on the(genetic) quaiity and quantity of the seed crop. If populations are structured on a local scale,and if neighbours are more related to each other than to individuals farther away, the thinningof the.st and may reduce inbreeding by consanguineous matings and may actualiy result in


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Towards a functional classification of f ores t systemsa t Sierra del Rosario Biosphere Resewe in CubaSince 1974, researchers a t the Instituteof Ecology and Systematics of theCuban Academy of Sciences havecarried out studies at the Sierra delRosario Biosphere Reserve in theprovince of Pinar del Rio of weste rnCuba. The predominant vegetationtype is tropical submontane evergreenforest, with areas cf thornyxeromorphic and herbaceouscommunities. The topography isdissected, with an iltitude rangeof 50-600 m. Based on 20 yeaFs'data, annual rainfall and temperatureaverage 2014 mm and 24,4QC,respectively.Over a period of about ten years,data have been collected from differentstands which could be classified asRestoring Primary Forest or MixedPrimary Forest - the formersubsclerophyllous at a site caiiedlocally Yagrumal-Majagual, the lat te rmesosclerophyilous at Vailecito.Two different groupings of functionalcharacteristics and performancecan be recognized in the accompanyingtable, the mesosclerophyllous forestbeing less productive than thesubsclerophyllous one. Caution isexpressed in presenting such acomparison. From the fore stmanagement standpoint, there isno intention to suggest that the

subsclerophyiious type should beimitated everywhere, since it is aforest type that is environmentallyrestricted. Also, the results obtainedfrom plant formations functionallyassociated with the tropical evergreensubmontane forest system cannotbe extrapolated to the semi-deciduousforest systems occurring in the Cubanplains.These caveats notwithstanding, afunctional classification of t ropicalforest ecosystems is being refinedby the Cuban research group. Itis based upon five major characters:distribution of litterfall over theenti re year; average degree ofsc1,erophyily; decomposition andnutrient cycling rates; distributionof rains and tot al precipitation;edaphic characte rist ics. In addition,in considering forest regenerationand management, account also hasto be taken of the original plantformations that were able to growunder the environmental conditionsof eight different localities studieda t S ierra del Rosario.Further information is given in severalsummaries and syntheses of the resul tsof ten yearsr research a t Sierra delRosario (Herrera e t al. 1986, in pressa, in press b).


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Functional characteristics of mesosclerophyllous forest (Vallecito) andsubsclerophyllous forest (Yagrumal-Majagual) at the Sierra del RosarioBiosphere Reservea

Functional Character Vallecito Yagrumal-Majagual

Root mat

Layer of dead lcaves

Seasonal to AbsentpermanentConstant Seasonal (only during

"dry" season)Hardness of rootlets Higher Lower

IBiomass of rootlets Higher Lower lLiving rootlets (%) Lower Higher IVertical distribution of rootlets Concentrated More uniformlyin the top distributedlayersDecomposition rate of leaves Lower Higher IDecomposition rate of rootlets Lower Higher IVertical distribution of VA Approximately Approximatelymycorrhizal extramatrical mycelia the same the same(MEVA)

Vertical variation of MEVA: rootlet Increasing Uniformlyratio (ug mg-1) with depth distributed

Production of MEVA Lower Higher IProduction of rootlets Lower Higher IGrowth rates of trees Slow growth Fast growth INutrient content of leaves Lower Higher IOrganic detritua in soi1 Higher Lower IDecomposer (faunal) populations Lower Higher Iproductivityb Lower Higher ITurnover rates Lower Higher (about double)a Actual figures corresponding to each character can be obtained romthe auchors.

Considering stands of the same age.


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form the production plantations; but, following additional testing and further selection, theyare used to develop the next generation of improvement, sometimes called the expandedbreeding population.There are many differe nt ways to make selections, establish seed orchards, to te st the progenyand continue to increase the genetic base of the programme. Such deta ils need to be carefullydeveloped for the species involved and the conditions of the selaction. Many reports, plansand some books have now been wr itten to provide these details,

3.5 TROPICA L FOREST SEED ECOLOGY D. Janzen-C. Vazquez-YanesThere is already an enormous data base on tropical seed biology in the literature and in humanmemory. This da ta base is growing rapidly while its source is shrinking even more rapidly.The relevance of any particular part of this data base to the management of mixed tropicalfore sts is extremely dependent on situation, just as is the case with the management of otherecosystem components. The components of the management process are the sit e (whatparticular forest), the management goal(s), the raw materia ls (plant and animal forestoccupants), and the competence of the managers. The guiding principles are 'know thyorganismsf and 'know thy habitat'. The habitat determines the relevance of any particularaspect of seed ecology. A thorough knowledge of the l iterature on tropical seed biology isunlikely to provide specific answers to any particular management problem, but on the otherhand, the seed biology litera ture often suggests relevant possibilities. While somegeneraliza tions about tropical seeds themselves are a necessary part of the managementframework, they are only distant or indirectly useful to a person actuaiiy attempting to growor manage a particular forest on a particular site. Of far greater use is understanding ofthe natural history and of system interactions in particular circumstances.Four processes inte rac t t o generate the seed "shadowlf that finaliy produces a seedling 'Tshadowll:seed production, predation, dispersal and dormancy. The processes that determine subsequentadult tree recruitment from that seedling nshadow'f are the same, except for the deletionof dispersal and the addition of growth. With this in mind, i t is evident tha t seeds and seedlingsare not the oniy juveniles potentially available for manipulation by the managers; for example,releasing 'teen-agel trees from cornpetition may be much more effective than planting seedsor seedlings of a desired species, as foresters well know.Seed productionIndividuai- and species-specific seed production pa tterns Vary within the individual, population,year, season and habitat. In general, species of the primary forest canopy wait longer (upto many years) between seed crops, and tend to be more synchronous at the level of thepopulation and habitat than are the species that form early successional forests. Within aspecies, an individuai's pattern of seed production among years is nearly always very situation-dependent rat her than locked into a geneticaiiy-fixed cuing system. Individuals in arboretaand other isolated circumstances are notorious for fruiting in years when the population atlarge does not fruit.There is enormous inter- and intra-specific variation in the size of the seed crops of individualtrees. A large crop may range from oniy a few dozen huge seeds to several million smallseeds. Likewise, it is commonplace for a given individual to Vary as much as 100-fold in thesize of i ts seed crop among years. Within an individual tree 's crop, the lightest viable seedsfrequently weigh less than half of the heaviest viable seeds.While seed production is often a crit ical part of the process tha t leads to restoration of apart icular forest, its study in the abs trac t' is of li tt le assistance in management. In general,habi tat disturbance increases seed yields for the surviving individuals, the pollinator serviceshave not been depressed (or altered to an extent where pbiiinators produce detrimentallyinbred genotypes through their patterns of pollen movement) and i f the new environnentis not detr imental to the tree 's reproductive physiology. The increase in seed production


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c o rn e s a b o u t d i r e c t l y t h r ou g h i n c r e a s e d r e s o u r c e s f o r t h e t r e e a n d i n d i r e c t l y th r o u gh d e c r e a s e dseed p reda t ion by spec ia l i s t i n sec t s and cer t a in fo rest - lov ing ver t eb ra te s . Th e increasedsee d y ields rnay be 'p l easan t ' fo r th e su rv iv ing f rugivores and seed-p red a to rs (as w e ll a s f o rt h o se p e r so n s t h a t a r e c o l l e c t i n g s e e d ), b u t t h e y w i l l a l s o s e v e r e ly a l t e r t h e p r o p o r ti o n aldernography of th e seed ra in on t0 th e s i t e . Whether th i s i s p re jud ic i a l o r benef i c i a l t om a n a g e m e n t d e p e n d s on t h e m a n a g e m e n t g oa ls .F lower ing i s o f t en consp icuous bu t i s no t a g o o d i n d ic a t o r o f w h e r e a n d w h e n m a t u r e s e e d swi l l be ava i l ab le , e i t her fo r co l l ec t ion o r d ispersa l by na tu ra l agen t s . L ikewise , som e t rop ica lt r e e s a r e f u n c ti o n a ll y m a l e , a n d t h e r e f o r e t h e i r d e n s i t y a n d l o c a t i o n a s f l o w e r in g i n di vi d ua l si s a poor ind ica to r o f th e dens i ty and loca t ion o f seed-bear ing individua l s.S i n c e s e e d p r o d u c t i o n v a r i e s s t r o n g l y a m o n g a n d b e t w e e n y e a r s , t h e t i m e o f y e a r a n d t h ey e a r i n w hi c h a r e f o r e s t a t i o n p r o j e c t o r a f o r e s t a l t e r a t i o n s c h e r n e be g in s w i l l s t ro n g ly a f f e c tth e subsequen t ou tc ome. L ikewise , as long apprec ia t ed by Malays ian fo res t e rs , t h e r!urnbero f y e a r s s i n c e t h e last rnas t s eed ing wi ii i n f luen ce th e nurnber o f seed l ings t ha t a re avc i il ablet o g e n e r a t e n ew t r e e s a t t h e t i r ne t h a t t h e f o r e s t is p e r tu r b e d. A s m e n t io n e d e a r l i e r , t r e e sth a t a r e on s t rong ind iv idua l , popu la t ion -wide o r hab i t a t-wide see d p roduct ion cyc les a rel ike ly to lose the i r synchron iza t ion when the hab i t a t i s remove d a round them. With see dproduct ion co rn ing a t i n t e rva l s , t he s eed (and hen ce seed l ing) dynarn ics o f a g iven ye ar shou ldn o t b e t a k e n a s n e c e s s a ri l y r e p r e s e n t a t i v e o f t h e s u b se q u e n t y e a rs . T h e s e s t a t e m e n t s ap p lyrnos t s t rong ly to p r im ary fo res t , bu t e ven young seconda ry fo res t c an have years o f high andlow see d production.W he n t r e e s a r e l e f t s t a n d in g o r e n c o u r a g e d a s s e e d t r e e s in m a n i p u l at e d f o r e s t , t h e y m u s tb e a c c o m p a n i e d b y a p p r o p r i a t e h a b i t a t f o r p ol i in a t or s a n d s e e d d i s p e rs e r s ; h o w ev e r,s u b s t i tu t i o n s o f o n e a g e n t b y a n o t h e r a r e q u i t e p o ss i bl e - even though , in any spec i f i c case ,t h e s u r r o g a t e s a r e l ik e l y t o g e n e r a t e a d i f f e r e n t p o i ii n a ti o n o r s e e d d i s p e rs a l p a t t e rn .In sum, a bou t t he on ly k ind o f pos i t ive man ipu la t ion th a t c an occu r wi th seed c rop p roduct ioni s s p ec i e s- s p ec i f ic r e d u c t i o n i n e n v i r o n m e n t a i c o n s t r a i n t s t o r e s o u r c e s f o r t h e a d u l t tree,u n d e r t a k e n i n t h e h o p e t h a t s u c h m a n i p u la t i on i s n o t f o l l ow e d by a c o n c o m i t a n t i n c r e a s ein seed p reda to rs . While t ree s may be b red fo r high seed y ie ld , t h e des irab i l i ty o f re l eas ings u c h t r e e s in to a mana ged hab i t a t w ii i depend on goal s. If s ee d c rop s are harves ted , t heh a r v e s t e r i s j u s t a n o t h e r k i nd o f s e e d p r e d a t o r ; h a r v e s t i m p a c t w i i i d e p e n d o n w h a t w o ul dh a v e b e en t h e f a t e o f t h e s e e d s t h a t a r e h a r ve s te d .Seed predationJ u s t as d i f f e r e n t s p e c i e s h a v e d i f f e r e n t d i s pe r s a i a n d ge r m i n a t i o n p r o p er t ie s , d i f f e r e n t s p e c i e sh a v e d i f f e r e n t s u s c e p ti b i l i ti e s t o d i f

unesco - rain forest regeneration and management

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