evaluation of prosopis juliﬂora properties as an

B O I S E T F O R Ê T S D E S T R O P I Q U E S , 2 0 0 8 , N ° 2 9 8 ( 4 ) 25GESTION DE LA RESSOURCE LIGNEUSEPROSOPIS JULIFLORA

Peter Sirmah1,2

Fred Muisu2

Francis Mburu2

Stéphane Dumarçay1

Philippe Gérardin1*

1Laboratoire d’études et de recherchesur le matériau bois (Lermab)Équipe de Chimie organique et microbiologieNancy UniversitéFaculté des sciences et techniquesBP 23954506 Vandœuvre-lès-Nancy CedexFrance

2Department of Forestryand Wood ScienceMoi UniversityPO Box 1125, EldoretKenya

Wood from Prosopis juliflora, which wasintroduced in Kenya in the 1970s as a means of slowingdesertification, is being used for both fuel and construction. Theresults of our evaluation show that the wood has high resistanceto white and brown rot pathogens, a high degree of impregnabilitymaking it suitable for use under severe conditions, and lowsusceptibility to termites. Its dimensional stability and mechanicalproperties are comparable to those of native Kenyan timberspecies. Its calorific value is similar to that of comparablefuelwood species. P. juliflora could help to remedy the woodscarcities currently prevailing in Kenya.

Evaluation of Prosopis julifloraproperties as an alternative to wood shortage in Kenya

Photo 1. The semi-arid lands of Kenya-Marigat, Baringo.Note the young stand of P. juliflora in the foreground.Photo P. K. Sirmah.

RÉSUMÉ

ÉVALUATION DES PROPRIÉTÉS DEPROSOPIS JULIFLORA COMPARÉES ÀCELLES D’ESSENCES AUTOCHTONESEXPLOITÉES AU KENYA

L’étude a pour objectif d’évaluer ladurabilité et les propriétés technolo-giques d’une espèce exogène duKenya, Prosopis juliflora, introduite audébut des années 1970 pour augmen-ter le couvert forestier et lutter contre ladésertification. La durabilité du dura-men vis-à-vis des champignons, testéedans des conditions de laboratoire,indique que le bois présente une bonnerésistance aux agents de pourritureblanche et de pourriture brune. Le boiscontient une teneur importante d’extra-ctibles, qui semble présenter un effetlimité sur l’inhibition de la croissancedes champignons. De plus, le bois estfacilement imprégnable, permettantd’envisager son utilisation dans desclasses d’emploi élevées après traite-ment adéquat. La résistance aux ter-mites évaluée dans des conditions delaboratoire et de champ indique unefaible susceptibilité du bois de P. juli-flora, qui semble fortement liée à laprésence des substances extractibles.Le bois présente une bonne stabilitédimensionnelle et les propriétés méca-niques supportent la comparaison aveccelles d’essences comme Pinus patulaabondamment utilisée au Kenya pourla construction. Le pouvoir calorifiqueest similaire à celui d’autres essencesdu genre Prosopis utilisées actuelle-ment comme bois de chauffage.L’ensemble de ces résultats montreque l’utilisation de P. juliflora commesource de bois d’énergie ou de bois deconstruction peut être une bonne alter-native à la pénurie de bois existant auKenya, permettant de réduire les pres-sions environnementales sur les forêtsnaturelles ou cultivées traditionnelles.

Mots-clés: extractible, durabilité,propriété mécanique, Prosopis juli-flora, valorisation, bois.

ABSTRACT

EVALUATION OF PROSOPISJULIFLORA PROPERTIES AS ANALTERNATIVE TO WOOD SHORTAGEIN KENYA

This study aimed to assess the durabil-ity and technical properties of Prosopisjuliflora, an exogenous tree species inKenya, which was introduced in theearly 1970s to improve biomass coverand rehabilitate arid and semi aridland. Laboratory tests to assess heart-wood resistance to fungi indicated thatthe wood was resistant to both whiterot and brown rot fungi. The heartwoodhad a high content of extractives, whichhave been demonstrated to have a lim-ited effect on fungal growth inhibition.Moreover, P. juliflora wood was easilyimpregnated using a standard vacuumpressure plant, so that additionalpreservation treatments can be consid-ered for use under severe conditions.Laboratory and field tests to assess ter-mite resistance indicated low suscepti-bility of P. juliflora wood, which seemscorrelated to the presence of extrac-tives. The wood is dimensionally stableand its mechanical properties com-pared well with those of Pinus patula, aKenyan wood species widely used forconstruction. Calorific value was con-sistent with that of other Prosopis woodspecies currently used as fuelwood.Taken together, these data indicate thatP. juliflora wood for fuelwood and con-struction can be a valuable alternativeto help remedy the wood shortage inKenya and reduce pressures on naturaland plantation forests.

Keywords: extractive, durability,mechanical property, Prosopisjuliflora, economic value, wood.

RESUMEN

EVALUACIÓN DE LAS PROPIEDADESDE PROSOPIS JULIFLORACOMPARÁNDOLAS CON LASDE ESPECIES AUTÓCTONASEXPLOTADAS EN KENIA

Este estudio tiene por objetivo evaluarla durabilidad y las propiedades tecno-lógicas de una especie exógena deKenia, Prosopis juliflora, introducida aprincipio de los setenta para aumentarla cubierta forestal y luchar contra ladesertización. La durabilidad del dura-men a los hongos, probada en condi-ciones de laboratorio, indica que lamadera presenta una buena resistenciafrente a la acción de los agentes cau-santes de pudriciones blancas y par-das. La madera tiene un contenidoimportante de extraíbles, que parecepresentar un efecto limitado en la inhi-bición del crecimiento de los hongos.Además, la madera es de fácil impreg-nación, lo que permite prever su utiliza-ción en clases de uso altas tras un trata-miento adecuado. La resistencia frentea las termitas, evaluada en condicionesde laboratorio y de campo, indica unasusceptibilidad baja de la madera deP. juliflora, que parece estrechamenteasociada a la presencia de substanciasextraíbles. La madera presenta unabuena estabilidad dimensional y suspropiedades mecánicas son compara-bles a las de especies como Pinuspatula, muy empleado en Kenia para laconstrucción. El poder calorífico es aná-logo al de otras especies de del géneroProsopis actualmente usadas comoleña. Estos resultados demuestran quela utilización de P. juliflora como fuentede leña o madera de construcciónpuede ser una buena alternativa a laescasez de madera en Kenia y permiti-ría reducir las presiones ambientalessobre los bosques naturales o cultiva-dos tradicionales.

Palabras clave: extraíble, durabili-dad, propiedad mecánica, Prosopisjuliflora, valorización, madera.

26 B O I S E T F O R Ê T S D E S T R O P I Q U E S , 2 0 0 8 , N ° 2 9 8 ( 4 )

WOOD RESOURCES MANAGEMENT

P. Sirmah, F. Muisu, F. Mburu, S. Dumarçay, P. Gérardin

PROSOPIS JULIFLORA

Context of the study

Forest ecosystems make up acomplex natural resource that providesenvironmental goods and services sup-porting social, cultural and economicdevelopment. It is therefore importantfor national development that thisresource is conserved, protected andsustainably used. Kenya and otherdeveloping countries are facing thechallenge of over-reliance on naturalresources. It is for this reason thatProsopis juliflora was introduced intoKenya’s arid and semi-arid lands in theearly 1970s, in order to remedy envi-ronmental problems, improve biomasscover and rehabilitate disused quarries(Choge et al., 2007). The species wasvalued initially for its ability to preventsoil erosion and to grow where nothingelse could (photograph 1). Over theyears, it spread rapidly and colonizedagricultural lands and pastures (Chogeet al., 2007). Its suckering ability aftercutting made it difficult to control.Today it has colonized a large propor-tion of Kenya’s arid lands, such as theTaita Taveta, Wajir, Mwingi, Marsabit,Isiolo, Mandera, Baringo and TurkanaDistricts (figure1). Inhabitants in theseareas are complaining about the treesforming impenetrable thickets andabout injuries due to thorns. Moreover,problems with livestock feeding on itspods have been reported. In oneunprecedented case, local communi-ties took the matter to the NationalEnvironmental Management Authority.P. juliflora has been reported in theprint media (Daily Nation, 22nd Febru-ary 2007) as gradually diverting theTana river from its course, thus affect-ing the Bura irrigation scheme as wellas overgrowing a large proportion ofthe road network in the 70 km2 KerioDelta (photograph 2).

P. juliflora is a fast-growing anddrought resistant plant originatingfrom South and Central America. Itgrows in all kinds of soil conditions,including wastelands, at altitudesranging from 0 to 1,500 m above sealevel, under mean annual tempera-

tures of 14 to 34 °C and annual rain-fall of 50 to 1,200 mm (Pasiecznik etal., 2001). Mature trees grow to 17 min height. The species is charac-terised by its twisted, greenish-brownstem, with axial thorns on both sidesof the nodes and branches. It isreported to dry out the soil and tocompete with grasses, particularly indry areas, and is therefore consid-ered in some areas as a weed (Chogeet al., 2007). Uses of P. juliflora pods,beans and gum as food supplementsand medicines for animals andhumans have been described (Barbaet al., 2006; Choge et al., 2007).A chemical characterization ofP. juliflora gum by Lopez et al. (2006)has indicated an arabinogalactanprotein with potential uses for bever-ages and pharmaceutical products,while fatty acids and free sugars inthe seeds and pods enhance its useas a food supplement (Sawal et al.,

2004; Silva et al., 2002). Antifungaland plant growth inhibiting alkaloidshave been isolated from its leaves(Nakano et al., 2004; Kishore,Pande, 2005) and associated with itsallelopathy. Bark and bark extractshave been shown to exhibit antifun-gal properties (Càceres et al., 1995).P. juliflora wood has been describedas a source of lumber, firewood, acti-vated carbon and barbecue charcoal(Kailappan et al., 2000; Goel, Behl,2001). There is considerable poten-tial for P. juliflora as a source of fibrefor the paper, paperboard and hard-board industry. The heartwood of dif-ferent Prosopis species contains sig-nificant amounts of wood extractivesand polyphenol compounds (Gold-stein, Villareal, 1972). A reddish-amber gum, with properties similar tothe gum arabica produced by Acaciasenegal, often exudes from the stemand older branches.


Figure1. Distribution of P. juliflora in Kenya.

Timber demand in Kenya is ris-ing each year, outstripping supply sothat a deficit of 6,841,000 m3 is fore-cast by the year 2020 (Mburu et al.,2005). State forests consisting of31% pine, 45% cypress, 10% euca-lyptus and 14% of other species coverabout 1,405,000 ha (some 2.4% ofthe total land area) while privately

owned plantations, consisting ofAcacia and Grevillea robusta, coverabout 70,000 ha. This evaluation ofthe technical properties of the woodof P. juliflora as an underexploitedexogenous species in Kenya’s aridand semi arid regions was carried outwith a view to its use as an alternativeto other declining wood resources.

Mater ials and methods

Determination of extractive content

in the wood

Mature P. juliflora wood was cutin Baringo (latitude 0°, 20’ N, longi-tude 35°, 57’ E), Kenya. The heart-wood and sapwood were separatelyground to fine sawdust powder usinga vibrating hammer mill, passedthrough a 115-mesh sieve and driedat 60 °C before soxhlet extraction withhexane, dichloromethane, acetone,toluene/ethanol mixture (2/1 v/v) orwater. 10g of wood powder wereextracted with 180ml of the solventfor 15 hours at a rate of 10 to12 cycles per hour. After extraction,the solvent was evaporated underreduced pressure and the residuewas vacuum-dried over P2O5 beforeweighing. Two methods based eitheron direct determination of extractivesafter solvent evaporation (directmethods, dm) or on the differencebetween the dry weight of sawdustbefore and after extraction (indirectmethod, im) were used to evaluateextractive contents.

The percentage of extractives wasevaluated according to the formula:

% dm

% im

where me is the weighed massof extracts after solvent evaporation,ms is the dry mass of the sawdustbefore extraction, and md is the drymass of extracted sawdust.

Resistance to fungal decay

Heartwood samples measuring35 mm x 25 mm x 5 mm (L, R, T) wereconditioned to a constant weight(mu) at a temperature of 20 ° to 22 °Cand a relative humidity of 60 to 70%.The theoretical dry mass (mt) of the

100)(

×−

=s

ds

m

mm

100×=s

e

m

m

Photo 2. P. juliflora growing wild and blocking a road in the Turkana Delta, Kenya. Photo P. K. Sirmah.

Photo 3. Fungal test with P. juliflora in a sterile chamber.Photo P. Gérardin.


PROSOPIS JULIFLORAWOOD RESOURCES MANAGEMENT

test samples was determined fromthe averaged percentage moisture (µ)obtained from similar samples driedat 103 °C according to the formula:

mt =100 mu

100 + µ

In a sterile chamber, two uv-ster-ilized samples were introduced intomalt-agar cultures of the white rot fun-gus Coriolus versicolor (cv) strain ctb863a and the brown rot fungi Poriaplacenta (pp) strain fprl 280Glocophyllum + trabeum (GT) strainEBW 109 and Antrodia species (an)strain cirad/2304/1. Each experimentwas repeated three times. Beech wood(Fagus sylvatica) was used as controlfor white rot fungi and Pinus sylvestrisfor brown rot (photograph 3).Incubation was carried out for threemonths at 25 °C and 70% RH. Decaywas assessed by determining the lossof mass using the following formula:

Mass loss (%) = (mt- mf )

x 100mt

where mf is the final weight ofdry samples after attack.

To understand the contributionsof extractives to resistance to wooddecay, fungal mycelium was grown in9 cm Petri dishes filled with 20 ml ofmalt-agar medium (30 grams malt,40 grams agar in 1 L) treated to 50, 100,500 and 1000 ppm of extracts. Controldishes were not treated with the extract.The extracts were introduced after ster-ilization of the medium (20 min, 120 °C,1 bar) by adding the necessary quantityof extract dissolved in 5ml of ethanol.The dishes were inoculated in the cen-tre of the malt-agar with a 10 mm por-tion of a healthy fungal colony.Incubation was carried out at 25 °C and85% RH. Growth was assessed every 2or 3 days by measuring the diameter ofthe colony estimated from the mean oftwo perpendicular diameters andexpressed as a percentage of availableroom for growth. Growth inhibition wascalculated when the diameter of thecontrol culture reached 9 cm, accordingto the formula:

growth inhibition (%) = 100 x (1 – d1/d0)

where d0 is the diameter of thecontrol culture and d1 the diameter ofthe culture in the presence of extracts.All experiments were duplicated.

Resistance to termite damage

Wood samples measuring 50 mmx 15 mm x 15 mm (longitudinal, radial,tangential) were exposed to Macro-termes natalensis termites in the fieldin accordance with a modified AWPAE7-93 (1993) field test standard usingstakes. Eighteen samples previouslySoxhlet extracted or not (see Table III)were exposed at a distance of 0.3 mfrom the termite nest and randomlyplaced 30 cm apart. Every month forsix months, three blocks, extracted ornot, were assessed for weight loss.Resistance to M. natalensis in the lab-

oratory was also assessed with theAWPA E1-97 (1997) standard method.Two test blocks measuring 30 mmx 10 mm x 20 mm (L, R,T) were placedin sterile glass jars with two cornersagainst the side of the container. Thejars, measuring 80 mm in diameterand 100 mm in height, contained150 grams of sterile sand and 30 mlof distilled water. Four hundred ter-mites were added to each jar at a ratioof 360:40 workers to soldiers respec-tively and incubated at 25 °C for28 days. The percentages of living ter-mites and weight loss (WL) in theblocks were determined after theexperiment as follows:

WL (%) =(m1- m2)

x 100m1

where m1 is the dried initial weightof the block and m2 the dried weightafter exposure to the termites. Pinussylvestris was used as the control.


Photo 4. Electron microscope scan of a heartwood section, showing vessels (dark spots).Photo F. Huber.

Anatomical features

Microscopic observations wereperformed with an environmentalscanning electron microscope (esemQuanta 200) for sapwood and heart-wood samples. The transverse sur-face of test samples was microtomedand analyzed without further prepa-ration. Photomicrographs were takenat different magnifications.

Physical and fuelcharacter istics

Moisture content was deter-mined using the oven-dry method.Basic density was determined fromfreshly cut wood samples using thewater displacement method:

wood density = wo / vo , wherevo is the volume of displaced waterand wo is the oven dried weight ofthe sample.

Ash content was determined asper astm d 3174-89 (1989). 1 g ofwood sample in a tared porcelaincapsule was subjected to a tempera-ture of 815 °C in a muffle furnace andthe amount of ash generated wasmeasured. Higher heating value wasdetermined as per astm d 2015-93(1993). 1 g of ground wood waspressed into a pellet and chargedinto a calorimetric bomb standard-ised by benzoic acid with a heatvalue of 26.453 mj/kg.

Moisture content

A freshly cut piece of P. juliflorawood was weighed (mi) and thendried in an oven at 103 °C until itsmass stabilized(md). Moisture con-tent (MC) was calculated as follows:

MC (%) = (mi-md)

x 100md

Determination of dimensional stabil ity

Twenty four samples of P. juliflorawere cut into 20 mm x 20 mm x 20 mm(L, R, T) pieces and dried at 103 ± 2 °C.Dimensions were measured to thenearest 0.01 mm using Veneer cal-lipers and their dry volume determined(v1). The samples were then put in adesiccator containing a saturated cop-per sulphate solution. The weight ofthese blocks was measured every twodays until they stabilised to a constantmass, indicating that the wood blockshad reached their maximum moisturelevel. Their dimensions were measuredagain and the wet volume determined(v2). The swelling coefficient (s) wasdetermined according to the formula:

s (%)

Mechanical strength test

Specimens from freshly cutmature P. juliflora were extractedfrom billets cut at breast height.Clear-wood specimens were sampledand tested according to BritishStandard BS 373:1957 using speci-mens obtained along and across thegrain. The specimens were dried toapproximately 12% moisture con-tent. Bending strengths (compres-sion and shear parallel to the grain)and hardness were tested. Their rup-ture and elasticity modulus and Jankahardness were evaluated. A cali-brated universal strength testingmachine (ustm) was used.

Treatabil ity

Industrial-quality CCA was usedat a concentration of 6% m/m(Tanalith-c, Arch Timber). Air-driedroundwood samples 140-150 mm indiameter and 2 m in length were vac-uum-pressure treated with an initialvacuum of 66,708 Pa for 15 min, apressure of 150,000 Pa for 4 hoursand a final vacuum of 66,708 Pa.Retention and penetration were deter-mined using the following formula:

100v

vv

1

12 ×−

=



Table I. Extractives from P. juliflora heartwood and sapwood (%).

Solvent Heartwood SapwoodDM IM DM IM

Hexane 2.4 2.7 1.8 1.9

Dichloromethane 3.4 3.7 1.9 1.9

Acetone 7.6 7.7 2.0 2.1

Toluene/ethanol 8.9 9.6 6.0 6.4

Water 10.6 10.8 6.2 6.6

DM: direct method; IM: Indirect method.

Table II. Percentage weight loss in wood samples after 3-month exposure to fungi.

FungiWood species C. versicolor P. placenta G. trabeum Antrodia

P. juliflora 1.5 2.3 3.1 2.5

P. sylvestris - 20.5 21.2 -

F. sylvatica 30.1 - - 24.5

retention = (w2 – w1) x c/v

where w1 is the mass of the air-dried untreated wood (kg), w2 is themass of the pressure-treated wood(kg), c is the solution concentration(%) and v is the sample volume.

Penetration was determined bymeasuring the depth (mm) impreg-nated by the chemical, radially fromthe periphery at mid-length.

penetration = [1-(r-r1)/r] x 100where r1 is the depth of preser-

vative penetration (cm) evaluatedvisually and r is the sample radius.

Results

Anatomicalcharacter istics

There is a marked differencebetween the yellowish sapwood ofP. juliflora and its dark brown heart-wood. The annual growth rings are dis-tinct, with marginal parenchyma bands.The vessels are either solitary or in clus-ters of 2 to 3 with a diffuse porous pat-tern. Earlywood and latewood vesselshad a mean diameter ranging from 110to 130 µm. Mean vessel density wasassessed at 6/mm2 (photograph 4).The diameter and density of vessels inP. juliflora can be described as usual forthis species. Villalba (1985) reportsvessel diameters in P. flexuosa of130 µm in earlywood and 40 µm in late-wood. Other authors do not distinguishbetween earlywood and latewood ves-sels and give medium diameters rang-ing from 40 µm for P. argentina(Villagra, Roig, 1997) up to 140 µmfor P. pallida (Lopez et al., 2005). Thedensity of vessels per square millimetrewas assessed as 10 in P. laevigata, 12in P. kunzei and 5 in P. palida (Lopez etal., 2005).

Extractive content

The quantities of extractive con-tained in the wood of P. juliflora arereported in table I. The two methodsused, based either on the weight ofextracts after evaporation of the sol-

vent or on the mass loss of extractedsawdust, gave close values indicatingthat practically no products were lostduring vacuum evaporation. Thequantity of extracts in both sapwoodand heartwood increased with solventpolarity. In the heartwood, the lowestpercentage of 2.4% extract wasrecorded with hexane, followed bydichloromethane with about 3.4%.The highest values, of 10.6% and8.9% respectively, were recorded withwater and a toluene/ethanol mixture.

Resistance to fungus attacks

Non-extracted non-dried heart-wood samples were exposed to fungalaction for 3 months, under sterile con-ditions, to evaluate natural resistance.The results showed high natural resist-ance to all tested fungi. In all cases, nosignificant weight losses were observed(table II), while beech and pine controlswere heavily degraded. The effect ofheartwood extractives on the growth offungi was investigated on a malt-agar


Extract concentration: 100 ppm

0

10

20

30

40

50

60

70

80

90

C. versicolor P. placenta Antrodia

C. versicolor P. placenta Antrodia

Gro

wth

Inhi

biti

on(%

)

Dichloromethane

Acetone

Toluene/Ethanol

Water


0

20

40

60

80

100

120

Gro

wth

Inhi

biti

on(%

)

Figure 2. Fungal growth inhibition by extracts at different concentrations.

medium to assess their effects on wooddurability. The results showed that in allcases, the extracts were more or lessefficient as fungal growth inhibitors atthe tested concentrations (figure 2).However, their action seems to stemfrom a fungistatic effect rather than afungicidal effect: development of themycelium on the treated mediumstarted after a more or less lengthy inhi-bition period (figure 3). During thisperiod, fungal activity was detected bythe formation of a coloured area aroundthe fungal inoculate. This behaviour isprobably associated with detoxificationof the medium by fungal enzymes,allowing further development of thefungus. Increasing the extract concen-tration increased the inhibition period.Similar observations were made for allthe extracts and fungi.

Resistance to termites

To assess resistance to termitesand check the influence of extractives,blocks (extracted or not) were sub-jected to termite action in the field for6 months and in the laboratory for28 days. The results are reported infigure 4 and table III respectively.Independently of the nature of theextraction and the test method,weight losses in the test blocks werelow for the unextracted blocks androse with increasing solvent polarity,while the pine blocks were heavilydegraded. These results suggest thatextractives play an important part innatural wood durability.

Physical and fuelwoodcharacter istics

Moisture content, swelling coef-ficient, ash content, density andheating values of P. juliflora andPinus patula, a Kenyan specieswidely used in construction, areshown in table IV. The results indicatethat P. juliflora wood is dimensionallystable with higher heating valuesconsistent with those of otherProsopis wood species currentlyused as fuelwood. Ash content is rel-atively high but consistent with thosegenerally found in tropical woodspecies (Goel, Behl, 1996). Theseresults suggest that P. juliflora is suit-able as fuelwood (photograph 5) orfor charcoal production (photograph6), mainly using traditional earth



01020

3040506070

8090

100

0 1 2 3 4 5 6 7 8 9 10 11 12 13Time (days)

Fung

alG

row

th(m

m)





Extract concentration: 1 000 ppm

0

10

20

30

40

50

60

70

80

1 2 3 4 5 6

Exposure Time (months)

Wei

ght

Loss

(%) Dichloromethane

Acetone

Water

Toluene/Ethanol

Hexane

Unextracted

Control

Figure 3. Fungistatic effects of acetone heartwood extractive against C. versicolor.

Figure 4. Effects of removing and retaining extractives on the resistance of P. juliflora heartwood to termites.

kilns (photograph 7). These tradi-tional earth kilns could be an inter-esting alternative to produce char-coal for local populations. Thedimensional stability and density ofP. juliflora wood could also be ofinterest for parquetry.

Mechanical properties

The elasticity and strength prop-erties of P. juliflora and P. patula areshown in Table V. The elasticity mod-ulus of P. juliflora is relatively highcompared to that of P. patula, butsimilar to that reported in the litera-ture. The rupture modulus ofP. juliflora was higher than for P. pat-ula, indicating good resistance underload and, consequently, valuablestrength properties. Compressionand shear strength parallel to thegrain corroborate MOR measure-ments. The values found were higherthan those reported, but consistentwith those of other Prosopis species.Janka hardness was lower than thatreported in the literature, but signifi-cantly higher than that of P. patula,indicating resistance to indentation.All these results indicate thatP. juliflora wood possesses themechanical properties required forconstruction purposes.

Wood treatabil ity

Even though most Europeancountries have banned or severelyrestricted the use of CCA treatedwoods, such treatments are still inuse in Kenya (Venkatasamy, 2005).


Table III. Effect of extract removal or non-removal on the resistance of P. juliflora heartwood to termites in the laboratory.

Solvent Workers Soldiers Weight Classificationsurviving (%) surviving (%) loss (%) of attack

Hexane 0 0 0.3 sound

Dichloromethane 8.5 4.5 2.5 light

Acetone 9 10 8.4 light

Toluene/ethanol 6 4 4.7 light

Water 8 7 12.8 moderate

Non-extracted 0 0 0.15 sound

Control 62 53 29.8 heavy

Table IV. Values of physical and fuel wood characteristics.

Species Physical properties Fuel wood characteristicsMoisture Density Dimensional Ash content Higher heating

content (%) (g/m3) stability (%) (%) value (kJ/g)

P. juliflora 32.6 0.828 2.3 2.84 21.50

P. patula 46.3 0.696 14.5 0.4 20.11

Photo 5. Mature P. juliflora used for fuelwood in Baringo District, Kenya.Photo P. K. Sirmah.

Sapwood penetration in P. juliflora(46.4%) is only half that of P. patula(100%) but higher than in other trop-ical hardwood species in the litera-ture, while retention ranged from36 kg/m3 in P. juliflora to 49 kg/m3 inP. patula. Sapwood is generally morevulnerable to biological degradationthan heartwood in most woodspecies (Grace, 1996). Both heart-wood and sapwood are susceptibleto fungi, termite and powder-post-beetle infestation, depending ondurability (Kamweti, 1992). Accor-ding to the Food and AgricultureOrganization (fao), the recom-mended cca retention for interior tim-ber not in ground contact, such astrusses or rafters, is 6 kg/m3, and8 kg/m3 for exterior timber not inground contact, such as doors andwindows. Timbers in ground contact,such as fence posts, railway sleepersand bridges, need a retention of12 kg/m3, timbers permanentlyimmersed in fresh water require16 kg/m3, and timbers immersed inseawater, for jetties and boat build-ing for example, require 24 kg/m3

(Fao, 1986). The relatively high reten-tion and higher sapwood treatabilityindicate that this species could be apotential alternative source of con-struction material for use undersevere conditions, for railway sleep-ers or fencing posts for example.Moreover, it can be assumed that theuse of more environmentally accept-able preservatives could lead to simi-lar results and reduce the impact oftreated wood on human health andthe environment.



Table V. Mean mechanical property values.

Species Compression parallel MOR MOE Shear parallel Hardnessto grain (kPa) (kPa) (MPa) to grain (kPa) (N)

P. juliflora1 73 320 124 100 15 200 20 100 7 300

P. juliflora2 62 050 113 700 14 200 15 030 13 000

P. patula 56 930 82 100 4 900 13 100 2 000

1Found; 2reported (http: www2.fpl.fs.fed.us/Techsheets/hardwoodNA/pdf-files/prosoeng.pdf).

Photo 6. Charcoal made from P. juliflora wood using traditional earth kilns.Photo P. K. Sirmah.

Photo 7. P. juliflora in a traditional earth kiln for charcoal production, Baringo, Kenya.Photo P. K. Sirmah.

Conclusion

Our study shows that P. juliflora(photograph 8) can be an alternativeto declining plantation timber inKenya for fuelwood, light construc-tion work and furniture manufacture.The wood properties tested are con-sistent with those of other Prosopisspecies grown in other parts of theworld, with the exception of a highextractive content not previouslyreported. The heartwood shows highresistance to fungi, and a lesserdegree of resistance to termites. Thehigh extractives content seems to bedirectly connected to termite resist-ance. Further studies are under wayto characterize the chemical compo-nents of the wood, bark, pods andleaves, with a view to fully realisingthe potential of this tree species.

AcknowledgementsThis work was supported by a girantfrom the French government throughthe Embassy in Nairobi.

References

ASTM D 3174-89, 1989. Standardtest method for ash in the analysissample of coal and coke.

ASTM D 2015-93, 1993. Standardtest method for gross calorific valueof coal and coke by the adiabaticbomb calorimeter.

AWPA E1-97, 1997. Standard methodof laboratory evaluation to determineresistance to subterranean termites.

AWPA E7-93, 1993. Standard methodof evaluating wood preservatives byfield tests with stakes.

BARBA A. P., FRIAS J. T., OLALDE V.,CASTANEDA J. G., 2006. Processing,nutritional evaluation and utilizationof whole mesquite flour (Prosopislaevigata). Food Science, 71 (4):S315- S320.

BS 373: 1957, 1957. Methods of test-ing small clear specimens of timber.

CÀCERES A., MENÉNDEZ H., MENÈN-DEZ E., COHOBON E., SAMAYOA B. E.,JAUREGUI E., PERALTA E., CARILLO G.,1995. Antigonorrhoel activity of plantsused in Guatemala for the treatmentof sexually transmitted diseases.Ethnopharmacology, 48 (2): 85-88.

CHOGE S. K., PASIECNIK N. M., HAR-VEY M., WRIGHT J., AWAN S. Z., HAR-RIS P. J. C., 2007. Prosopis pods ashuman food, with special referenceto Kenya. Waters SA, 33 (3): 419-424.

FAO, 1986. Wood Preservation Manual.Italy, Food and Agriculture Organization.

GOEL V. L., BEHL H. M., 2001. Geneticselection and improvement of hardwood tree species for fuel wood pro-duction on sodic soil with particularreference to Prosopis juliflora. Bio-mass and Bioenergy, 20 (1): 9-15.

GOEL V. L., BEHL H. M., 1996. Fuel-wood quality of promising treespecies for alkaline soil sites in rela-tion to tree age. Biomass and Bioen-ergy, 10 (1): 57-61.

GOLDSTEIN I. S., VILLARREAL A.,1972.Chemical composition and accessi-bility to cellulase of Mesquite wood.Wood Science, 5 (1): 15-20.

GRACE J. K., 1996. Susceptibility ofcompressed fiber to termite attack.Forest Products, 46 (9): 76-78.

KAILAPPAN R., GOTHANDAPANI L.,VISWANATHAN R., 2000. Productionof activated carbon from Prosopis(Prosopis juliflora). Bioresource Tech-nology, 75 (3): 241-243.

KAMWETI D. M., 1992. Growth andutilization of Grevillea robusta aroundMt Kenya. In: Grevillea robusta inForestry and Agro forestry. Nairobi,Kenya, C. E. Harwood (ed.), ICRAF.

KISHORE G. K., PANDE S., 2005. Inte-grated management of late leaf spotand rust diseases of groundnut(Arachis hypogaea L.) with Prosopisjuliflora leaf extract and chlorotha-lonil. International Journal of PestManagement, 51 (4): 325-332.

LOPEZ B. C., SABATÉ C. A., GRACIA C. A.,RODRIGUEZ R., 2005. Wood anatomy,description of annual rings andresponses to ENSO events of Prosopispallida H.B.K., a wide- spread woodyplant of arid and semi-arid lands ofLatin America. Journal of Arid Environ-ments, 61: 541-554.

LOPEZ Y. L., GOYCOOLEA F. M., VALDEZM. A., BARCA A. M. C., 2006. Mesquitegum: Alternative of industrial use.Interciencia, 31 (3): 183-189.

MBURU F., MUISU F., SIRMAH P., GER-ARDIN P., 2005. Impregnability ofGrevillea robusta using the sap dis-placement method. Bois et Foretsdes Tropiques, 286 (4): 65-72.

NAKANO H., NAKAJIMA E., HIRADATES., FUJII Y., YAMADA K., SHIGEMORI H.,HASEGAWA K., 2004. Growthinhibitory alkaloids from Mesquite(Prosopis juliflora [Swartz] D.C) leaves.Phytochemistry, 65 (5): 587-591.

PASIECZNIK N. M., FELKER P., HARSHG., HARRIS L. N., CRUZ J. C., TEWARIK., MALDONADO L. J., 2001. TheProsopis juliflora-Prosopis pallidacomplex, a monograph. In: HIDRA.United Kingdom, Coventry.

SAWAL R. K., RATAN R., YADAV V. S.,2004. Mesquite (Prosopis juliflora)pods as a feed resource for livestock– a review. Asian-Australasian animalSciences, 17 (5): 719-725.

SILVA J. H., OLIVEIRA J. N. C., SILVA E. L.,JORDAO F. J., RIBEIRO M. L., 2002. Useof Integral Mesquite (Prosopis Juliflora(Swartz) D.C.) pods meal in the Japan-ese quails feeding. Revista Brasileirade Zootecnia, 31 (4): 1789-1794.

VILLALBA R., 1985. Xylem structureand cambial activity in Prosopis flex-uosa DC. IAWA bulletin 6: 119-130.

VILLAGRA P. E., ROIG F. A., 1997. Woodstructure of Prosopis alpataco and P.argentina growing under differentedaphic conditions. IAWA, 18: 37-51.

VENKATASAMY R., 2005. Industrial woodpreservation in Kenya. Present status-Future prospects. IRG/WP 05-30385.


Photo 8. A one-year-old P. juliflorain Baringo District, Kenya. Photo P. K. Sirmah.

evaluation of prosopis juliﬂora properties as an

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