Biological Considerations in the Utilization of Racosperma Auriculiforme and Racosperma Mangium in Tropical Countries with Empha

2 42 l ForestJournal ScienceTropica f o 6(4): 422-443

BIOLOGICAL CONSIDERATION UTILIZATIOE TH N SI N OF RACOSPERMA AURICULIFORME AND RACOSPERMA MANGIUM TROPICAN I L COUNTRIES WITH EMPHASIS ON ZAIRE

P.D. Khasa*,

Centre, Recherche,de. Biologieen Forest/ere, Faculte Foresterie.de Geomatique,de et Universite. Lavtil, Sle- Foy, Quebec, G1K 7P4, Canada

G. Vallee

Direction de. Recherche,la Ministere Forelsdes Quebec,du rue,700 Einstein,2 Ste-Fo\, Quebec CAPW8, 3 Canada

J. Bousquet+

Centre Recherchede. Biologieen Forestiere,, Faculte, Foresteriede Geomatique,,de, et Universite Laval, Ste- Foy, Quebec GlK 7P4, Canada

Received July 1992 ______

KHASA, P.D., VALLEE, G. & BOUSQUET, J. 1994. Biological considerations in the utilization of Racospenna auriculiforme and R. mangium in tropical countries with emphasis on Zaire. Racusperma miriculiforme (.Acacia auriculiformis) and R. mangium (A. mangiuw), two fast-growing species belonging to the Leguminosae family, have been introduced into Zair r industriaefo l fuelwood plantation r socia wels fo s a s a l agroforestry purposes repore W . r current herou n eo t knowledg biologicae th n eo l consideration e utilizatioth n si f boto n h specie tropican i s l countries with emphasis n Zaireo e taxonomTh . d ecologyan y , reproductive biolog d breedinyan g systems,, genetic diversity, biolic interactions, silvicultur d presenean t use f theso s e species c examinedar . Because these species will pla a ymajo r rol n reforestatioi e n programme e nexth tr fo decades developinn i s g countries suc s Zairea h e th , necessit genetie th r fo yc improvemen f theso t e specie s wel a ss adaptability a l , site trial d silvicultnraan s l requirement e discussear s n relatioi de increasth o t nf o e plantation productivity.

Keywords: Acacia - biotic interactions - genetic diversity - luelvvood plantations, reproductive biology - taxonomy - silviculture - social agroforestry - Zaire

KHASA , VALLEED. . BOUSQUET,]P ,& . ,G . 1994. Pertimbangan-pertimbangan dari segi biologi dalam pengurusan Racospertna auriculiforme . mangiumR n da i d

* Present address: Department de Biologie, Faculte des Sciences, B.P. 190, Universite, de Kinshasa, Zaire * Author for correspondence: Fax: (418) 656-3551; Tel: (418) 656-5085 3 42 Journal of Tropical Forest 3 Science44 - (4)2 6 42 :

negera-negara tropika dengan penekanan kepada negara Zaire. Dua spesies dari famili Leguminose, iaitu Racosperma auriculiformis (Acacia auriculiformis). R n da mangium (A. mangium), telah diperkenalkan di Zaire untuk industri ladang kayu jugn da a i untuap k perhutanan tani sosial i siniD ., kami melaporkan dengan pengetahuan semasa kami, tentang perimbangan biologi penggunaan kedua-dua spesies ini di negara-negara tropika dengan memberi tumpuan kepada negara Zaire. Taksonomidanekologi,pembiakan biolog sisten da i m pembiakbaikan,kepelbagaian genetik, interaksi biotik, silvikultu penggunaan rda n semasa kesemua spesie dikajii sin . Keperluan untuk memperbaiki genetik spesie i sertin s a kebolehsesuaian da n keperluan silvikultur yang berkaitan dengan peningkatan produktiviti ladang dibincangkan i adalaIn . h keranakedua-dua spesie akai sin n memainkan peranan utama dalam program-program penghutanan semula dalam dekad-dekad yang akan datang di negeri-negeri membangun scperti Zaire.

Introduction

n manAi s y tropical Sub-Saharan African countries, shiftin d moderan g n agriculture, fuelwood gathering foresty , firedr d savannas n i an s d selectivan , e logging system have been e maireporteth ne b cause o t d f o losf foresso s t biodiversity in Zaire (Khasa et al, in preparation). In order to overcome the problems associated with forest depletion and to maintain a sufficient supply of woo r fuelwooddfo , timber d chemicalsan , , reforestation with fast-growing tree species is being intensified in many tropical countries. It is estimated that in Sub- Saharan Africa, at least 25 million ha of plantations and woodlots with fast-growing tree e requiresar satisfo dt e demanth y r fuelwoofo d othed an d r rural needs (Schonau 1990). Most forest tree plantation tropican si l countries consis exotif to c fast-growing tree species (Evans 1982, Zobel et al. 1987). Their growth and yields generally exceed those of natives, attaining for instance 30 m3 ha'1 y~l or more with Eucalyptus in Congo at 7- y rotation (Vigneron & Delwaulle 1990). However, the monoculture of exotics is often criticized, because of apparent lack of adaptation e exoticoth f s use theid dan r susceptibilit pestso yt betteA . r knowledge th f eo performanc adaptatiod ean exoticf no thein environmentsw i ne r s therefori s e crucial before proceedin largo gt e scale introductions same th t e A .time longe th , - term environmental impact introductioe th f so exoticf no oftee sar n unknown. This may be depicted by the slow decomposition of litter of introduced Casuarina equisetifolia along the coast of Senegal. Native species might represent a logical alternativ unfortunatelyt ebu , little researc bees hha n devote theo dt their me fo rus in reforestatio land nan d reforestatio tropice th n ni s (Butterfield 1990). Eucalyptus spp. and Pinus spp. are generally selected for exotic monocultures severad an l industrial tree planting programme timber s fo puld ran p production have been established with these species (Martin 1987, Campinho Ikemors& i 1989, Moutanda 1990, Schonau 1990, Vigneron & Delwaulle 1990). However, polar and non-polar allelochemicals fro e leavemth f Eucalyptuso s have been showo nt inhibit growth of annuals, to decrease biodiversity in the area of eucalypt forest, causo t d e an economic los o agriculturat s l crops (Kohl Sing& i h 1990). These problems are also exacerbated by the high competitiveness of some Eucalyptus specie nutrientr sfo d watean s r (Martin othee 1987)th n r handO . , Pinus radiata has been used successfully in, silvopastoral systems by the forest industry in the journal of Tropical Forest Science 6(4): 422 - 443

southern temperate zones of New Zealand, Chile and Australia (Knowles el. al. 1990). Several shrub treed san s fro e genermth a Acacia sensu lato, Calliandra, Cassia, Gmeiina, Gliricidia , Lcucaena, and Tectona have been used in tropical countries for fuelwood plantation agroforestrd san y purposes (National Academ f Scienceyo s 1980, National Research Council 1983). Fast-growing leguminous, actinorhizal, othed an r nitrogen-fixing tree oftee sar n preferre ruran di l community plantations for agroforestry systems theio t parn e i ,r abilittdu improvo yt nitrogee eth n status of soils in symbiotic association with either Rhizobium, Bradyrhizobium, Azorhizobiurn, Sinorhizobium, Pholorhizobium, or Frankia (Baker 1990, Brewbaker et al. 1990, Sprent & Sutherland 1990), and also due to the increase in the uptake of immobile nutrients, especially phosphorus, in symbiotic association with endomycorrhi/al and/orectomycorrhi/alfungi (Khasarfrt/. 1990,1992,Bolan 1991,Molinar 1992). al t fe . Many of these species are early colonizers of cleared or disturbed sites, being mycorrhi/al dependen becomind tan g less importan lesd san t competitiv sois ea l fertility increases (Molina et al. 1992). They play a major role in soil nitrogen accretio organin i d nan c matter accumulation, contributin earlo gt y soil development (see Baker 1990). Of the exotic leguminous plants selected as multi-purpose trees for planting in the tropical countries, Racosperma auriculiforme (Cunn. ex Benth.) Pedley (Acacia auriculiformis) mangium. R d an (Willd.) Pedley, comb. nov mangium). A ( . oftene ar cite havins da highese gth t priority (National Academ Sciencef yo s 1980, National Research Council 1983, Turnbull 1987, 1991) presene Th . t review focusee th n so biological considerations in the utilization of both species in tropical countries with emphasis on Zaire. Their taxonomy and ecology, reproductive biology and breeding systems, genetic diversity, biotic interactions, silvicultur used e ean sar discussedIntroductio. n of Racosperma auriculiforme and R. mangium into Zaire

R. auriculiforme and R. mangium have been introduced as plantation species into many countries of tropical Asia, America, and Africa (Catinot 1984, Turnbull 1987, 1991, Boland et al. 1990, Souvannavong 1990). Trial plots have been established in some western, central, southern African countries (Table 1), and in other countrie f tropicaso l AsiAmericad aan . Accordin Kankolonggo t Kamd oan i (1989), R. auriculiforme was introduced into Zaire in 1967 as part of a programme funde Fooe Agriculturd th dy an d b e Organizatio Unitee th f no d e Nationth d an s United Nations Development Programme (FAO/UNDP). R. mangium was introduced into Zair Kinzone n 197th i e t 9a o arboretum situatenortheasm k 0 d15 t from Kinshasa. However seee th , d origin botf so h introduced Racosperma species were not recorded. Because of the outstanding amenity attributes of R auriculiforme (Jim 1990) fe,a w hectare urbaf so n plantin around an gn i d Kinshasa City have been established, mainly for ornamentation and energy biomass production. Zairen I , reforestation activities have been supervise Service th y db e National de Reboisement (SNR) since 1978. In 1979, the Centre Forestier Kinzono 5 42 Journal of Tropical Forest Science 3 44 6(4)- 2 42 :

Table 1. Some African countries where Racosperma auriculiforme and R. mangium have been introduced

. auriculiformeR . mangiumR Country

West Africa s ye s ye Benin Ivor)' Coast yes Niger yes Nigeria yes Sierra Leone vcs

East Africa

Kenya yes s ye s ye Tan/ania s ye Uganda

Centra] Africa Burundi yes Cameroon yes yes Congo yes yes Zaire ves ves

Southern Africa s ye Malawi Zimbabwe yes s ve South Africa

initiate introductioe dth f exotino c species suc thoss ha Racosperma,f eo Eucalyptus, d Pinusan n Kinzoni o arboretu e Batekth n o me Plateau. From 197o 9t 1985,about 300 ha were planted, including R. auriculiforme, Cassia siamea, Eucalyptus camaldulensis, Millettiad an laurentii. 1985n I funa , d named "Fonde sd Reconstitu-tion du Capital Forestier" (FRCF) was created in order to promote reforestation activities throughout the country. Since 1986, with the assistance of e Europeath n Economic Community e privatth , e society HVA-Holland Agro Industries bv is carrying out an industrial tree planting programme on 8,000 ha in Bateke th e platea r energufo y biomass production e fast-growinth f O . g trees selected, R. auriculiforme was the major species being planted. Recently, the potential use of R. mangium has also been demonstrated (Khasae/a/. 1993a). Both Racosperma beinw specieno ge usesar reforeso dt t degrade nutrientd dan - impoverished sites generally covered by Hyparrhenia and Imperata grass across countrye th . Local non-governmental organization wels a sBelgians a l , German, Italian, and Swiss cooperation programmes, and the "Projet Pilote d'Appui au Reboisement Communautaire" (PPARC), funded since 1988 by the Canadian International Agency (CIDA), are also involved in community forestry.at the village level. In 1988, about 750,000 seedlings mainly of R. auriculiforme, were produced by the farmers through the PPARC, of which 70% were outplanted (Kankolongo & Kanu 1989). The total allocated surface for reforestation Journal of Tropical Forest. Science 6(4): 422 - 443 426

programme s approximateli s y 112,00 Zairn i a 0eh (Pagez Ntoty& o 1990)l al n I . of these reforestation activities, R. auriculiformeand R. mangium should play a major and increasing role.

Taxonom ecologd yan y

R. auriculiforme and R. mangium are members of the Leguminosae family (subclass Rosidae, order Fabales, subfamily Mimosoideae, tribe Acacieae). Based morphologyn o , palynology, chemistr heartwoodf yo seedsd san , cyanogenesid san susceptibity to rusts, Pedley (1986) has recently divided the genus Acacia sensu lato into three genera: Acacia Miller, Senegalia Rafinesqu Racospermad an e Martius. e majoritTh f Australiao y n acacias have been placee genuth n i ds Racosperma Martius (Pedley 1987a), which contains about 850 species grouped into four sections (sc Racosperma, uninerved species, sc Plurinervia including Acacia sc Juliflorae, sc Lycopodiifolia and sc Pulchella). R. auriculiformeand R. mangium belong to the traditional section Juliflorae, a large group of 219 species having a mainly tropical distributio e northwes th e nort th d n an hi n t (bue t th als n i o southwest) of Australia (Boland et al. 1990). Acacia Miller is a pantropical genus of some 200 species best represented in Africa and South America with about eight endemic Australian species (Pedley 1987b). The genus Senegalia has about 150 species grouped into two sections (sc Senegalia and sc Filicinae), and has about e samth e geographic range than Acacia witrepresentativeo htw northease th n si t Australif o a (Pedley 1987b). Although Pedley's proposal (Pedle t acceptey no 1986 Internae s th wa y ) db - tional GrouStude th Mimosoideaer f yo p fo resultes ha t i , furthen di r research into genue th s which wil beneficiae lb elucidatinn li relationshipe gth Acacz'e th f so a sensu lato (Playfor . 1992)r opinional t ou de n .I , classificatiothiw sne n from Pedley might righte b . Apart from reasons raised above Australiae ,th n acacia quite sar e different fro Africae mth n acacia morphologicae th t sa ploidd an l y levels. Australian acacias are diploid while African acacias are polyploid (Atchison 1948, Joly 1991). Using the unitA f Acaciao sDN S 5 sensu lato, e Australiath n specie f subgso . Phyllodineae (equivalen Racosperma)o t t grouped togethe unia s a rt separated fro othee mth r subgenera Aculeiferum (equivalen Senegalia)o t Acaciad an (Playfor . 1992)al t de . Further work migh e requireb t confiro dt f thesmi e three subgener f Acaciaao shoul e elevate b de generi th o t d c ran s proposea k Pedley b d y (1986). Work involving the estimation of morphological, biochemical and molecular phylog- enies (Strauss et al. 1992) and their levels of congruence (Bousquet et al. 1992) in the genus Acacia sensu lato and related species (Mimosoideae) should be under- taken. Sampling should be done in all parts of the distributions, including Oceania, Asia, Africa Americad an , . e phytogeographTh ecologd yan f botyo h Racosperma specie e welar s l docu- mented (Turnbull 1986, Atipanumpai 1989, Boland et al. 1990). R. auriculiforme and R. mangium are indigenous to Australia, Papua New Guinea, and Indonesia (Turnbull 1986, Atipanumpai 1989, Bolan . 1990)al t de . These specie wele sar l adapted in the humid and subhumid tropics on several soil types from near Journal of Tropical Forest Science 6(4): 422 - 443 427

witd a an leve h, se aboutemperaturo m t le 0 th t50 e rangin g34"Co t fro " n I m. 16 their natural habitat e annuath , l rainfall range frod s2,00an mo , t fro 0 0mmm 90 1,500 to 3,000 mm, for R. auriculiforme and R. mangium respectively (Turnbull 1986, Bolan . 1990)al t de . mangiumR . commonls i y altitudefounw lo t a d , alone gth mangrove forest fringes associated with Rhizophora d sppMelaleucaan . spp., or more often along forest margins sympatrically with Dillenia alata Banks, R. cincinnatum (F. Muell.) Pedley, comb, nov., R. aulacocarpum (Cunn. ex Benth.) Pedley, comb, nov. Eucalyptusd ,an tessellaris Muell. F . (Atipanumpai 1989). During the Quaternary periods there were severe stresses on alpine, coastal, and coralline environments so that the present distribution of R. mangium is of very recent origin a resul s f a ,individual o t s that have survive smaln di l scattered refuges during the glaciations (Moran et al. 1989a). R. auriculiforme is opportunistic and very mobile, colonizing many ecological niches. The species is fairly primitive and. may have evolve n raio d n forest fringes sympatrically wit . aulacocarpumhR d an R. crassicarpum (Cunn. ex Benth.) Pedley, comb, nov., but thriving better in marginally more difficult sites than its two allied species (Boland et al. 1990). Newly-germinated seedlings of R. auriculiforme and R. mangium produce com- pound-bipinnate leaves which are transformed into veined phyllodes (flattened leaf stalks weeks) w aftefe . auriculiformea rR . phyllode c5 e aboum0. ar s wid + 2 t e and four to nine times as long as wide (Pinyopusarerk 1990), while those of . mangiumR (Nationam c 0 largee 1 o abou t ar X p l u 5 , Researc2 t h Council 1983). e steTh m . auriculiformeforR f mo variables i , ranging from crooke d heavildan y branche singlo dt e straigh dominand an tgreate e th r fo ttrere parth e f heighto t , diameten i m c 0 besn 8 o r d talt m site an l 0 3 s - (Pinyopusarerreachin5 2 o t p gu k 1990) . mangiumR . develops straight, clear bole d cone-shapesan d canopy with relatively short, occasionally self-pruning branches s heighIt . n reaco t ca t p hu 30 m and its diameter up to 90 cm on best sites (National Research Council 1983). Flowers of R. auriculiforme are yellow and are in spikes or racemes up to 8 cm long, with peduncle longm uppe e m pairn i th , 7 n si rs2- phyllode axilth f so e (Figure 1). Pods of about 1.5 cm wide and 6.5 cm long are flat, cartilaginous or rather woody, glaucous, transversally veined with undulate margins. They are straight initially but become very twisted with irregular spirals at maturity (Figure . Flower 3) . mangiumR f o se whit ar r creao e spiken mi o t e p colouar su d an r 10cm long (Figure 2). Initially green and straight, the pods twist and intertwine irregularl blackish-brown yi n spiraled cluster t maturitsa y (Figur. e4) r preliminarOu y result chromosomn so e counts fro root-tie mth p cells indicate diploidy with a chromosome number of 2n = 26 for both species. However, out of 14 specimens examined e chromosomth , e numbe e individuaon e n i on r f o l populatio auriculiformeR f no . Thiinvestigatey indicat22 sma = n 2 es possibldwa e variation in chromosome number among and within populations of R auriculiforme. These early obsen'ations are consistent with previous reports (Brewbaker 1987, Darus l989).

Reproductive biology and breeding systems

Knowledge about the reproductive biology and the breeding systems are Journal Tropicalf Sciencet o Fores 6(4): 422-443 428

Figur . Flowerine1 g spike. auriculiformeR f o s

Figure 2. Flowering spikes of R. mangium Journal of Tropical Forest Science3 44 6(4)- 2 42 : 429

Figur . eFruit3 . aunculiforiR f so

Figure 4. Fruits of R. mangiun 0 43 Journal of Tropical Forest. 3 Science44 - (4)2 6 42 :

importan propea r fo t r understandin e distributionth f go d life-historiean s f so . auriculiformeR . mangium,R d an their population genetics efficiend an , t domesti- cation and use of their genetic resources. In Zaire, these species produce abundant flowers from the third year but collection of seeds is conducted only from the fourth year. Despite that no detailed phenological studies are available, the two species prove to show synchronous flowering in plantations during the second period. The first flowering occurs only for R. auriculiforme between February and April and ripe seeds are available from May to July. The second flowering occurs for both species between June and August and ripe seeds become available from September to October. Variations in timing and intensity of flowering and fruiting may also occur, depending on behavioural changes of insect pollinator d environmentaan s l conditions (Sedgle . 1992)al t e y . Furthermore, even though synchronous flowering is observed, this may take place at different times from yea yeao rt r (Sedgle l 1992)a t ye . e havW e determine e floradth l formula . auriculiformeR r efo e flowerth : e ar s hermaphrodite wit joine5 h d sepals unjoine5 , d petals, numerous hypogynous stamensanda single ovary with 1 locule, 1 carpel and numerous ovules ((S(5) P(5) Ao°G°° u)). Similar investigation . mangiumR n so indicated that flower here ar s - maphrodite wit 5 joineh d sepals unjoine5 , d petals, numerous hypogynous stamen singla ovuled 0 1 s an e o ovart s 5 ((S(5 d y witan l ) locule h1 P(5pe ° r )ca A° 1 , G5-10 u pollee ))Th . n grain Racosperman i s generalle ar y grouped into polyads commonly consistin grain6 1 f go s (Sedgley 1987, Sedgle . 1992)al t ye . rooo N t sucker e observear s plantationn di f boto s h specie d sproutinan s g appears to be poor after cutting at the ground level (Khasa, unpublished results). Better results have been obtained elsewhere when stumps are cut at high level ) (i.e.,fro e groun1m mth d (Pinyopusarerk 1990). Vegetative propagatioa vi n juvenile rooted cuttings is possible for both species and the role of indole butyric acid phytohormone (1BA n increasini ) e numbegth rootine th f root o rd gsan succes bees sha n shown (Khas . 1994a)al t ae vitron I . cultur bees eha n achieven di other countries with R. auriculiforme (Mittal et al. 1989) and R. mangium (Crawford &Hartney 1987, Darus 1991, GalianaeZa/. 199l a,b), and layering and grafting have also proved to be successfully applicable (Liang 1987, Pinyopusarerk 1987). Agamosperm neves yha r been reporte Racosperman di . R. auriculiforme and R. mangium are both allogamous, hermaphrodite, and monoecious. Insect pollinations appea e rul s th bee ra e visitore ar sth f o s flowers. Flowers lack nectaries but have extra-floral secretory glands located on the phyllodes (see Sedgley et al. 1992). R. mangium shows high outcrossing rate n naturai s l stands (Mora exotin 1989a. i al d t nce an )plantation n Zairi s e (Khas . 1993)al t ae . From allozyme data derived fro 1 populationm1 f o s R. mangium (Moran et al. 1989b),the extent of inbreeding as estimated from

Wright's fixation index (F]S) was moderate. The survey of progeny arrays at the more variable loci strongly suggested that R. mangium is predominantly outcrossing (see Mora . 1989b)al t ne . Similar results were obtaine y Khasb d a

et al. (1994b) with F]S being near 0. As pointed out by Sedgley (1987), and Sedgley and Griffin (1989), there are three floral mechanisms which promote outcrossing 1 43 Journal of Tropical Forest Science 3 44 6(4)- 2 42 :

in Racospenna : (1) These species may show protogynous dichogamy with the stigma receptive to exogenous pollen before the pollen is released from the anther Andromonoec) (2 . y with mal hermaphroditd ean e flowere samth en o s plant also promotes pollen transfer from flowe flowero t r Self-incompatibilit) (3 . y or self-sterility, the failure of pollen to produce seed set in the same and related individuals is the third outcrossing mechanism explained by prezygotic and postzygotic barriers. Seed abortion detecte s unfillea d d seedsw occurlo a t a s leve botn i l h Racosperma specie d thian ss coula consequenc e b d levelw lo sf eo of self-pollination (Khasa et al. 1993c). R auriculiforme is closely related to R. aulacocarpum and sometimes confused with R. leptocarpum (Cunn. ex Benth.) Pedley, comb. nov. and R. polystachyum (Cunn x Benth.e . ) Pedley, comb. nov. (Pinyopusarerk 1990). Hybridf o s R. auriculiforme X R. mangium have been reported both in natural stands and in exotic plantations (Skelton 1987, Kian . 1989al t ge , Wickneswari 1989, Sedgley . 1992) eal e t genetiTh . c distance o speciesbetweetw e th ,n estimate d from allozyme data, was in the range of values representative of conspecific taxa (Khasa et al. 1994b). Therefore, selection of suitable provenances and artificial hybridization between R. auriculiforme and R. mangium should be pursued in the breeding programme thesf o s e species. These hybrid havy ma se great potential for plantation forestry by combining desirable properties of the parental species e straightnessucth s ha f o stes m form e resistancth , heartroo t e othed an t r economical characters. These hybrids could be further introduced into intensive clonal silviculture via rooted cuttings or tissue culture.

Genetic diversity

Several type f biochemicaso moleculad an l r genetic marker e useb o dt n sca estimat e leveleth f genetiso c diversit f foresyo . 1992)al t t tree e faro i S . ,s(L only biochemical genetic markers have been successfully use Racosperman di (Moran et al. 1989a,b, Wickneswari & Norwati 1993, Khasa et al. 1994b). Based on allozyme markers . mangiumR , s showe morb wa o nt e genetically depauperate than R. auriculiforme (Moran et al. 1989a, b, Khasa et al. 1994b, Wickneswari & Norwati 1993, ) (Table 2). The proportion of the total diversity residing among populations alss (Gi ) o substantia r botfo l h species d somewha(Tablan , e2) t

higher than valueST s recorde r largelfo d y outcrossed angiosperm tree species (Hamric Lovelesk& s 1989, Baw . a1992) al 1992t e i .L , Therefore e absolutth , e amount f genetio s c diversite relativth d eyan distributio f thino s diversite yar both important components to consider in designing efficient selection and breeding programme r thesfo s e species . auriculiforme,R r Fo . these observations e corroboratear y resultb d s from field provenance trials establishe severan di l countries (Turnbull 1991), which have show greana t dea variatiof lo growtn ni h traits within and among populations. For R. mangium, provenance trials have also shown significant amount variatiof so n that coul exploitee db selection di n programmes (Atipanumpai 1989, Khasa 1993a). Journal of Tropical Forest Science 6(4): 422 - 443 432

Tabl . Allozyme2 e diversit Racosperman yi auriculiforme . mangiumR d an a

Species N n Ap Pp H Reference (0.99)

(auriculiformeR. 2 19 0.146 0.18 Mora , (1989a)al t ne 18 99 1.5 39.8 0.081 0.27 Wickneswar Norwal& i i (1993) 13 1 . 1852 9 1. 0.122 0.18 Khasarta/. (1994b)

/{. mangium 1 1 30 1.1 12.7 0.017 0.31 Moran et al. (1989b) 13 18 1.5 24.3 0.004 0.09 Khumi . (1994bal t e )

Abbreviations: N = number of populations surveyed, n = number of gene loci surveyed, Ap = the average a numbe f alleleo r r locu spe r population spe p (0.99 P ,average th )= e proportio f polymorphio n c locr pe i population (0.99 criterion) average th - ,H e expected proportio genetie th f no c diversit populatioo t e ydu n

differentiation. e

Biotic interactions

. auriculiformeR . mangiumR d an e involve ar symbiotin di c associations with natural population f endomycorrhizao s l fung d Rhizobiuman i r Bmdyhizobiumo (Khasa el al. 1990) (Figures 5,6 & 7). We failed to find natural ectomycorrhizal associations in plantations of Racosperma in Zaire whereas this was reported with Thelephora spp. elsewhere (Dart el al. 1991) or with Pisolilhus spp. (Amadou Ba, personal communication 1992).

Figure 5. Intercellular vesicles (v) and byphae (h) in an endomycorrhizal . atiriculifnrmerooR f o t Journal of Tropical Forest Science 6(4): 422 - 443 433

Figur . Arbusculee6 s n (ara n )i Figur . Nodulee7 . aunculijormR f so induced endomycorrhizal root by wild Rhizobium (sensu lato) showing of R. auriculiforme a branched form

Reddel d Warrean l n (1987) stressee potentiath n do l benefit f artificiallo s y inoculating Acacia sensu lato with mycorrhizal fungi as did Roughley (1987) for inoculation with either Rhizobium or Bradyrhizobium. Following in vitro inoculation . auriculiformeoR f . mangium,R d an only Bradyrhizobium spp. strains formed effective N-fixing nodules (Galian . 1990)al t ae . Inoculation wit e ectomycorrhizahth l

fungu2 s Boletus suillus (L. ex. Fr.) stimulated plant growth of R. auriculiforme as well as P and N uptake, as compared to controls (Osonubi et al. 1991). However, growth reduction occurred after inoculation with a mixture of Glomus and Acaulospora (Osonub . 1991)al t e i . Positive effects were recorde biomase th n do s accumulatio nutriene th d nan t uptak. auriculiformeR n i e seedlings undee th r influenc triplf eo e inoculants (Rhizobium Glomus+ fasciulatum+ Bacillus megaterium), followe doubly db singld ean e inoculants (Mohamma Singd& h 1988). According theso t e authors e combinatioth , n Rhizobium Glomus+ fasciculatum e mosth s t wa effective among dual inoculants. Height growt auriculiforme. R f ho s equallwa y stimulated, resulting in higher total N and P in the seedlings, after dual inoculation f Glomoso fasciculatum, marginata,. G r Scutellisporao persica with Rhizobium whereas only both Glomus species were effective for R. mangium (Dela Cruz el al. 1988). Therefore, in the sites where indigenous efficient strains of mycorrhizal fungi and Rhizobium (sensu lato) are lacking, screening and inoculation in the nurseries with more efficient and competitive strains may increase forest productivity. Moreover, the appropriate selection of the best tree genotypes well adapted to particular site conditions is likely to render the whole process more efficient. Insec pathogenid an t c interactions occu nurseriesn i r , suc thoss ha e involving nematodese th , stem borer insect r insectso s whic t seedlinghcu s (Figure, 9) & 8 s presence th d an f Oidiumeo fungus (Figure 10). However damage th , e causey db these types of pest is generally negligible. In plantations, R. auriculiforme seems to be more susceptible to stem borers (Figure 8) while R. mangium is more susceptible to heartrot and also to stem borers during drought. The presence of ants livin branchen go symbiosin i s s wit treee protecy hth ma s t them against Journal of Tropical Forest Science3 44 6(4) - 2 42 : 434

phytopathogenic organisms and assure better growth (Wiersum & Ramlan 1982). We also noticed in one site in Zaire (Muanda), an unidentified spider species which builds nests with phyllodes of R. auriculiforme, resulting in yellowish phyllodes that could severely impair growth othen I . r countries, Sinoxylon species were reporte importans da t pests that cause serious damag Rac.ospmnan ei plantations (Hutacharer Choldumrongkun& l 1989).

Figure 8. Commons hole of Figure 9. An insect pest which . auriculiformeR o t e du damageats thseedlinge nurser f Racospermaso y stage stem borer insects

.10

Figur . Oidium0 eI fungus covering phyllode f Racospermaso nursere ath t y stage

Silviculture

Seedin mose th s gti popula propagato t y rwa e both species (National Academy of Sciences 1980, National Research Council 1983). Because of the seed-coat dormancy in Rncosperma the seeds should be pre-treated in order to speed up Journal of Tropical Forest Science 6(4): 422-443 435

and obtain uniform germination (Khasa 1993b). Soaking seeds in concentrated thed an nn rinsinsulphurimi wit n water0 p 3 hmi ta g r 5 o the 1 ,c5 r 1 acim fo r dfo produce e besth d t result r laboratorfo s y testin r operationa fo s wel a gs a l l application (Doran & Gunn 1987, Khasa 1993b). Boiling water from which the heat source is removed and in which the seeds are placed and soaked until the water is cool (12-24 h) seems the most suitable and economical method to break seed coat dormancy for social forestry programmes at the village level in Zaire (Khasa 1993b). Newly-germinated seedlings grow well in shady conditions for a limited time and full sunlight is required for their full development. Direct seedin thrego t wito eh tw pre-treate d seeds place eacn di h planting hole represents an attractive reforestation strategy but it requires extensive site preparation and post-seeding maintenanc e smalth f lo e germinating seedlings. Generallye th , survival rate is low if weed competition is not appropriately controlled (Gerkens & Kasali 1988). Growing seedling n blaci s k polyethylene bags during three months in nursery resulted in survival rate higher than 90%, and this method was very successfu establishinn i l g good stockin plantinf go g grasslan e treeth n si d areas (Khasa 1993a) (Figures 11, 12 & 13). The planting spacings used for fuelwood TO3 X . Vegetativ2 d an m e 5 propagatio2. plantation X 5 2. n e a stils ni ar t s a l experimental scal t earlebu y results with cutting e encouraginar s g (Khas. al t ae 1994a). Eve frequenf ni t stana t d fringes, sexual natural regeneratio scarcs ni n ei exotic stand t takesbu s place readily afte stande th r s have been cut-over (Khasa, unpublished results).

Figure 11. Preparation of containerized Figure 12. Representative average growth seedlings using black polyethylene bags of R. auriculiforme, provenance #16355, reachin month9 t ga aboum n si 2 1. t provenanca e Bateketh tria n o el Plateau, Zaire Journal f Tropicalo Forest Science3 44 6(4) - 2 42 : 436

Figur . Representative13 e average growt . mangiumR f ho provenance #13460, reachin month9 t ga provenancaboua m n si 0 1. t e trial on the Bateke Plateau

e meaTh n annual incremen . auriculiformeR f o t n vero y poo d acidian r c soils of the Bateke plateau is 12 m ' ha-' y-' at 7-year rotation (Gerkens & Kasali 1988) productivite .Th improvee b n ca y mor y db e intensive managemeny b d tan using propagule f genetio s c superiority n earlI . y evaluatio . auriculiformeR f no and R. mangium provenance trials in Zaire (Khasa 1993a), R. auriculiforme showed higher plasticity than R. mangium, and therefore, more stability across the sites. It grew well from 110 to 1300 m of altitude. In the sites where R. mangium was physiologically suited, such as Bateke plateau, some provenances were outper- forming . auriculiformethosR f o e (Khasa 1993a). However . mangiumR ,e th s wa least salt-tolerant species and did not thrive in saline soils at 6 km from the Atlantic coasts with 100% mortality (Khasa 1993a). In this site, two putative hybrids, showing morphological characters intermediate between these two species, grew well. They showed fine branchin d apicagan l dominance whicy ma h lead to good stem form as compared to pure R. auriculiforme trees which generally show crooked stems.

Uses

As exotics, both species hav greaea t potentia tropice th n i l s because thee yar suitable for firewood, charcoal, pulpwood, timber, tanning, fodder, honey production, green manure, agroforestry, erosion control, windbreaks, shade ornad an , - mentation (Turnbull 1986, 1987, 1991) Zairen .I . auriculiforme,R bees ha n selected maie asth n plantation specie r large-scalfo s e biomass productio f fuelwoodno . R. auriculiforme is also planted along the streets in cities as an ornamental tree. Because of its poor stem form (Figure 14 ), it is not suitable for timber production. Journal of Tropical Forest Science 6(4): 422 - 443 437

Alternately . mangiumR , gooa s dha stem form suitabl r timbeefo r production (Figure 15) specifis .A c gravit qualitd yan fibrf yo e make possibl productioe eth n of kraft and soda anthraquinone pulps (see Pinyopusarerk 1990), these species could be intercroped in blocks with Pinus spp. and Eucalyptus spp., which have been retained by the National Forestry Action Plan of Zaire for pulp production (Anonymous 1990). Local textil d cigarettan e e industries could alse barus ok product f Racospermao s stic s tannin preparatioa r h fo sogd e an sdy a yellof no w and brown colours (see Pinyopusarerk 1990). The adhesive properties of bark extract of R. mangium may also be attractive for local particleboard manufacture l 1989a (Moht e r , AsmRahidn No Wa am & 1990) .

Figur10-year-olA . e14 d stan. auriculiformeR f do Bateke th n o e plateau For which the seed origin is unknown. This typical poor stem for generallms i y ohserve plantationn di . Trees usually reach about 15 m in height and 18 cm in diameter at breast height at 10 year old journal of Tropical Forest Science3 44 - 6(42 42 ): 438

Figure 15. A 10-year-old stand of R. mangium in the arboretum of Centre Forestier de Kinzono on the Bateke plateau for which the seed origin is unknown e steTh m. forgrowtd an m h characteristicf so . mangiumR generalle ar y superio thoso t r e of R. auriculiforme

n I Zaire a promisin, g agroforestry system with Racosperma includee th s intercropping of R. auriculiforme and Manihot esculenta Crantz (Hanns Seidel Foundation, unpublished results). This system combines high productivity with the ability to improve soil fertility (Chakraborty & Chakraborty 1989). However, stunting and reduced yield were observed when leguminous crops such as Arachis hypogaen and Vigna unguiculata were cultivated after a forest fallow of R. auriculiforme (HVA-Holland Agro Industries bv, unpublished results). These results may be explained by either antagonistic relationships among soil minerals, toxicity, or allelopathic effects. Further research is needed to clarify these observations. Similarly, seed germination and growth of Tamarindus indica was allelopathically inhibited in soil which has been previously used for germination and growth of R. auriculiforme (Setiadi & Samingan 1978). Aqueous extracts of bark and leaf of A. nilotica, mostly tannins, inhibited seed germination of arable crop t witbu sh differing intensity, tomato bein mose gth t sensitiv sunflowed ean r e leasth t (Swaminatha . 1989)al t e n . Journal of Tropical Forest Science 6(4): 422 - 443 439

Contrary to R. auriculiforme, R. mangium has only been recently introduced into Zaire and the first research trials were established in 1989 (Khasa 1993a). For the present, no information is available on the potential use of R. mangium in agroforestry. However, a rehabilitation trial of littoral soils for the regeneration of old coconut palm groves was successfully implemented in Ivory Coast with this species (Dupuy & Kanga 1990). By increasing reforestation activities throughout the country particularly in agroforestry systems, Racosperma species may not only contribute to maintaining or increasing soil fertility, but may also provide at the village level various products and other environmental benefits. By simultaneously or sequentially using best suited companion arable crops and/or animal same th en o spiec f landeo e th , benefit f integratino s g Racosperma species into Zaire agroforestry programmes should be maximized.

Acknowledgements

e thani (CRBFW L . kP , Universite Laval, Quebec . RousseaD d an ) u (FAO, Rome r thei)fo r valuable comment n previouo s s draft f thio s s manuscriptd ,an G. F. Moran (CSIRO) and C. Gervais (Universite Laval, Quebec) for useful informations and stimulating discussions. Financial support was provided by a grant froe Canadiamth n International Development Agency . (CIDAD . P o t ) Khasa.

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