Introduction

Fast-growing species such as Acacia mangium,A.auriculiformis,and A.mangium×A.auriculiformis hybrids are suitable for the pulp and paper industry.Acacia species are grown extensively in South-East Asia with over 10 million hectares planted.In Indonesia,A.mangium has become the dominating plantation pulpwood species during the last 10 years as an excellent source of fi bre for papermaking(Hillman 2002;Malinen et al.2006).In addition,plantations of fast-growing species like A.mangium and A.auriculiformis have been promoted by the Vietnamese Government to ensure adequate supplies for pulp consumption in the country(Hai 2009).The natural hybrid of A.mangium and A.auriculiformis has an increased growing demand,especially in the pulp and paper industry due to its superior growth rate,better adaptation to a wide range of soils and better pulp yield than both parent species(Yamada et al.1990).

Although Acacia species are important to pulp and paper industries,little is known about the wood properties of this genus.There is little information to justify the wood quality of all the different genotypes within these species.It is well documented that natural variation in the quantity and quality of lignin has not been studied extensively even within a model species.Furthermore,wood properties may vary greatly due to factors such as age,environment,changes in climate and fertilization(Fagerstedt et al.1998).This scarcity of information raises concerns about wood properties from intensively managed forests,as similar volumes of wood may have very different values due to the presence of signi fi cant portions of juvenile wood which may result in low wood quality(Zobel and van Buijtenen 1989).

One of the most important characteristics necessary for effective wood utilization in the pulp and paper industry is the quantity and composition of lignin of the stem wood.Approximately two-thirds of all virgin wood pulp(recycled fi bers excluded)is produced by the kraft process that uses NaOH and Na2S to extract≥90% of the lignin.The rate of this process is believed to be enhanced by a high S:G rate(Kondo et al.1987;Tsutsumi et al.1995).Therefore wood with low amounts of lignin and high syringyl to guaiacyl ratios is often associated with improved pulping ef fi ciencies(Huntley et al.2003).This is because lignin is removed from wood chips during the pulping process,usually by chemical pulping and bleaching process,which are expensive,energy-extensive and environmentally unfriendly(Boerjan et al.2003).A high percentage of lignin in wood requires higher chemical consumption during pulping and this gives lower pulp yields(Pinto et al.2004).The objective of this study is to determine the variation and association of lignin contents,mean stem densities,and fi bre lengths of A.mangium,A.auriculiformis and their hybrid.Correlations between phenotypic traits are explored in order to understand their effects on wood development,which could be used for selection and improvement of desired traits.The data generated are useful for selection breeding and improved utilization of these fast-growing plantation species for the pulp and paper industries.

夜蚊会叮人，饭蚊会爬饭，于是人们千方百计地想把它们赶尽杀绝。这时蚊虫们说：“贪婪又愚蠢的人们，你们尽管使招儿吧！我们的存在是你们无法改变的，这是大自然的生存法则。

Materials and methods

Sampling

Mean stem densities of both sapwood and heartwood were signi fi cantly different(Table 2).High mean values were recorded for A.auriculiformis(699.84 g/cm3)followed by the hybrid(633.55%g/cm3)and A.mangium(584.0 g/cm3)(Table 3).Generally,heartwood showed highermean stem densitiescompared to sapwood(Table 2).Mean stem density was higher than 0.50 g/cm3 indicating that Acacia’s are hardwood species with hybrids of intermediate wood densities.Besides lignin content and composition,mean stem density is by far the most important parameter for measuring wood quality.Mean stem density is closely related to pulp yields and pulping properties(Malan et al.1994;Wimmer et al.2002).Wood with densities of 470–550 kg/m3is well suited for pulp production(Hai 2009),while higher density wood is suitable for construction(Barnett and Jeronimidis 1990).The mean stem density of A.auriculiformis was higher than for A.mangium and their hybrid.These fi ndings are consistent with empirical studies conducted in Vietnam where the mean stem density of A.auriculiformis was higher than A.mangium at the same age(Kha 2001).Furthermore,A.auriculiformis wood is regarded by saw millers to be denser and harder than the Acacia hybrid and A.mangium(Hai 2009).The moderate mean stem density and lignin content of the hybrid suggest that this genotype is wellsuited for the pulp and paper industry.Wood basic density was typically lower in fast-growing trees than in slowgrowing trees(Quang et al.2010).This study reveals that wood densities and lignin contents of the investigated species were inversely correlated.Strong negative correlations were observed in all the genotypes.Growth differences may also be due to differences in stand density due to their capacity to capture more sunlight,moisture and nutrients to accelerate tree growth(Jiang et al.1994).Hu et al.(1999)demonstrated that lignin reduction in transgenic aspen was accompanied by higher cellulose content together with substantially enhanced growth rates.A signi fi cantly negative correlation was reported between lignin content and diameter growth in a hybrid backcross population of Eucalyptus(Kirsten et al.2004)and in Populus(Kim et al.2009).Mean stem densities for both sapwood and heartwood were signi fi cantly different(Table 2).High mean values for A.auriculiformis(699.84 g/cm3)were followed by the hybrid(633.55%g/cm3)and A.mangium(584.0 g/cm3)(Table 3).Generally,heartwood showed highermean stem densitiescompared to sapwood(Table 2).Mean stem density was higher than 0.50 g/cm3 indicating that Acacia are hardwood species with the hybrid of intermediate wood density.

Fig.1 Wood disc(Dbh=54 cm)of A.mangium showing the sapwood and heartwood zone with bark removed.Locations where sapwood chips were sampled are in white circles while heartwood wood chips were sampled are in black circles

Lignin analysis

A comparison of the extractives of sapwood and heartwood clearly demonstrates a higher percentage present in the heartwood(Table 1).The highest extractives were present in A.mangium in both sapwood and heartwood followed by the hybrid.However,high extractive values are not correlated with high lignin content.The average F values,mean signi fi cance,standard deviation and mean ranking for lignin,mean stem density and fi bre length in sapwood and heartwood traits are presented in Table 2.Overall,lignin content,mean stem density and fi bre length differed signi fi cantly among different individuals of the two species and their hybrid.High mean lignin content was observed for A.mangium(36.25%)followed by A.auriculiformis(33.91%)and interspeci fi c hybrid(31.99%)respectively(Table 3).Lignin content ranged from 18.16 to 46.58%within A.mangium,22.54 to 42.09%within A.auriculiformis and 21.43 to 38.45%for the interspeci fi c hybrids(Table 2).However,overall mean values of lignin content were lower in A.auriculiformis(33.90±9.33)compared to A.mangium(36.24±13.71).High standard deviation values for both species clearly indicate a wide range of diversity present within and between different individuals of the two species.For high quality pulp and yield,low lignin content requires low processing.Wood is composed of cellulose,hemicelluloses,lignin and extractives formed into a cellular structure,with cellulose accounting as the major component(Yang et al.2003).Wood with low amounts of lignin and high syringyl to guaiacyl ratio that affects the lignin extraction during kraft process which uses NaOH and Na2S has improved pulping ef fi ciency and paper quality(Kondo et al.1987;Tsutsumi et al.1995;Huntley et al.2003).Lignin content in A.mangium was higher than in A.auriculiformis and the hybrid.High lignin content in A.mangium implies lower pulp yields,as largeamounts of chemicals have to be used during the pulping process(Pinto et al.2004).Lower lignin content in the Acacia hybrid suggests better pulp yields than from parent species and its importance for the pulp and paper industry(Yamada et al.1990).Sapwood tissues generally gave better yields as they require less bleaching compared to heartwood tissues which contain high extractives,indirectly increasing chemical consumption.Our results indicate that the amount of extractives in sapwood was lower than that in heartwood tissues which can result in higher pulp yields.Our fi ndings of lignin content of A.mangium between xylem stress compression wood and xylem stress tension wood(unpublished)support fi ndings of Yamashita et al.(2007).Cellulose content in wood forming on the upper side of branches is higher compared to the lower sides of branches(Qiu et al.2008).Wood forming in vertical stems has cellulose and Klason lignin contents that are intermediate between upper and lower branch wood(Qiu et al.2008).Hence our sampling strategy de fi nitely provides accurate justi fi cation on the lignin amount in the two species and their hybrid.

“中央厨房”包括聚合型和内控型两种。人民日报社的“中央厨房”是典型的聚合型“中央厨房”，大众报业集团、河南日报报业集团、湖南日报社等地方媒体也建立了此类“中央厨房”。而一些媒体则搭建了内控型“中央厨房”，《经济日报》的“中央厨房”就是此类典型。

Core samples were collected without removing the bark.Fresh sample mass was measured with an electronic balance immediately after collection,followed by oven-drying at 75°C to a constant weight and reweighing to determine the dry mass.Based on the fresh volume of the collected samples,measured from the length of the sample(5 cm)and the diameter of the increment borer(0.25 cm)and their dry mass,the mean stem density of each sample(in terms of dry mass per fresh volume)was calculated(Guendehou et al.2012).

Core sampling for mean stem density

衡诸二者，将绿色发展理念经由“绿色原则”在《民法典》中实现并引至“物权编”过程中，宜遵循“基本原则—具体规范—个案适用”的逻辑思路。

Fibre length analysis

A one-way ANOVA using the MINITAB software was used to test whether signi fi cant differences(p≤0.05)exist within and between A.mangium,A.auriculiformis and their hybrid for Klason lignin,mean stem density and fi bre length.If the differences were signi fi cant,Duncan’s multiple range test(DMRT)was used to compare the mean values.Association between the three traits was analyzed by Pearson’s correlations.

Data analysis

Fibre length of sapwood and heartwood was determined based on TAPPI T 232-om-85.A 10-mm thick and 5-mm wide radial stick of sapwood and heartwood was sawn from each disk.Samples were softened by gentle boiling in water till they sank,and were then macerated by dipping in boiling 5%glacial acetic acid at 100°C.2 mL of glacial acetic acid and 5 g sodium chloride were added hourly into the boiling solution until the fi bre was softened.The fi bres were stained with safranin and a drop of the macerated sample was placed on a slide and oven-dried for 1 h.Fifty wood fi bres each of sapwood and heartwood were measured for length using a pro fi le projector(Nikon V-12,Japan)under 50×magni fi cation.

Results and discussion

Lignin content of sapwood and heartwood tissues were determined using procedures described in TAPPIT 222-om-88(Schoening and Johansson 1965).Klason lignin was determined from the extractive free wood.One g of wood meal was placed in a 100 mL beaker,with 15 mL of 72%H2SO4added.The mixture was subjected to occasional stirring for 2 h at room temperature.The subsequent solution was transferred to a 1 L Erlenmeyer fl ask,topped up with 575 mL of deionized water and re fl uxed for 4 h.The solution was fi ltered using crucible no.4 and the acid insoluble lignin was determined gravimetrically.

Table 1 Klason lignin and extractives in sapwood and heartwood tissues in A.mangium(Am),A.auriculiformis(Aa)and Acacia hybrids(Ah)of 10-year-old trees

Am48,Am54,Am59=Acacia mangium samples from different provenances indicated by different numbers.Aa62,Aa71,Aa78=Acacia auriculiformis samples from different provenances indicated by different numbers.Ah111,Ah112,Ah113=different interspeci fi c hybrids(A.auriculiformis×A.mangium)

Mean extractives Am48 40.19±0.609 1.43±0.079 41.81±0.621 9.83±0.312 41.0±0.605 5.63±0.158 Am54 21±0.432 4.51±0.089 21.24±0.301 11.08±0.364 21.12±0.352 7.79±0.162 Am59 42.5±0.302 2.59±0.062 43.78±0.421 11.74±0.375 43.14±0.358 7.17±0.159 Mean 34.56±0.441 2.84±0.066 35.61±0.510 10.88±0.371 35.09±0.462 6.86±0.215 Aa62 22.54±0.257 3.34±0.068 22.18±0.586 13.16±0.425 22.36±0.412 8.25±0.221 Aa71 36.76±0.399 3.24±0.062 36.73±0.685 10.35±0.356 36.75±0.521 6.79±0.223 Aa78 42.09±0.133 2.97±0.062 43.16±0.364 7.56±0.289 42.63±0.268 5.26±0.178 Mean 33.79±0.243 3.18±0.063 34.02±0.516 10.36±0.345 33.91±0.358 6.77±0.168 Ah111 39.27±0.338 4.02±0.075 34.67±0.516 11.35±0.354 36.97±0.425 7.68±0.202 Ah112 38.45±0.420 2.34±0.067 38.52±0.615 8.04±0.279 38.49±0.524 5.19±0.189 Ah113 21.44±0.391 3.04±0.060 19.66±0.245 8.61±0.286 20.55±0.315 5.83±0.152 Mean 33.05±0.315 3.13±0.059 30.95±0.431 9.33±0.302 32.00±0.354 6.23±0.181 Sample Klason lignin in sapwood tissues(%)Extractives in sapwood tissues(%)Klason lignin in heartwood tissues(%)Extractives in heartwood tissues(%)Mean Klason lignin(%)

Table 2 F-statistics and signi fi cant mean values for lignin content,mean stem density and fi bre length in Acacia mangium,Acacia auriculiformis and interspeci fi c hybrid

**Highly signi fi cant at 0.01 level of signi fi cance,genotypes sharing similar letters are not signi fi cantly different

Fibre length heartwood F value=2748** F value=1724** F value=1324** F value=1445** F value=869.4** F value=827.6**Am48 41.19±0.649(F) 42.98±0.673(F) 551.25±1.707(B) 600.50±3.109(B) 0.860±0.008(B) 0.84±0.005(B)Am54 18.16±0.446(A) 19.64±0.301(A) 622.00±3.915(D) 566.00±2.449(A) 0.842±0.005(A) 0.82±0.005(A)Am59 46.58±0.338(G) 48.93±0.547(G) 506.00±4.690(A) 658.25±3.500(E) 0.870±0.008(B) 0.86±0.006(B)Mean 35.31±0.425 37.18±0.534 559.75±3.434 608.25±3.019 0.86±0.007 0.84±0.005 Aa62 22.54±0.260(C) 22.17±0.586(B) 758.50±3.109(H) 790.00±5.163(H) 0.920±0.008(C) 0.90±0.009(C)Aa71 36.76±0.399(D) 36.73±0.688(D) 674.25±4.573(F) 680.75±3.095(F) 0.977±0.005(E) 0.97±0.008(E)Aa78 42.09±0.133(F) 43.16±0.364(F) 635.75±4.425(E) 659.75±2.500(E) 0.960±0.008(D) 0.95±0.008(D)Mean 33.79±0.243 34.02±0.516 689.5±4.145 710.16±3.256 0.95±0.007 0.94±0.008 Ah111 39.27±0.338(E) 34.67±0.516(C) 584.00±6.928(C) 631.25±2.986(D) 1.110±0.008(G) 1.10±0.008(G)Ah112 8.45±0.420(E) 38.51±0.637(E) 586.00±3.915(C) 621.50±3.415(C) 1.077±0.005(F) 1.07±0.008(F)Ah113 1.43±0.391(B) 9.65±0.245(A) 689.50±2.645(G) 689.00±3.265(G) 1.110±0.008(G) 1.10±0.008(G)Mean 33.05±0.315 30.94±0.431 619.83±4.516 647.25±3.158 1.09±0.0.007 1.09±0.008 Genotypes Lignin sapwood Lignin heartwood Stem density sapwood Stem density heartwood Fibre length sapwood

Table 3 Overall mean values of lignin,mean stem density and mean fi bre length in Acacia mangium,Acacia auriculiformis and interspeci fi c hybrids

Genotypes Mean lignin(%) Mean stem density(g/cm3) Mean fi bre length(mm)Am48 42.08±0.635 575.88±2.145 0.85±0.008 Am54 18.90±0.332 594.00±3.156 0.83±0.005 Am59 47.76±0.412 582.12±4.012 0.86±0.008 Mean 36.25±0.442 584.00±3.251 0.85±0.007 Aa62 22.35±0.325 774.25±4.058 0.91±0.008 Aa71 36.75±0.451 677.5±3.624 0.97±0.008 Aa78 42.62±0.248 647.75±3.148 0.96±0.008 Mean 33.91±0.341 699.84±3.256 0.95±0.007 Ah111 36.97±0.415 607.63±4.658 1.10±0.008 Ah112 38.48±0.512 603.75±3.685 1.07±0.005 Ah113 20.54±0.325 689.25±2.685 1.10±0.008 Mean 31.99±0.354 633.55±3.489 1.09±0.007

Wood samples from 10 year-old trees were collected from Plot W,Experimental Field,UKM,Bangi,Malaysia.Three trees varying in diameter at breast height of each species and hybrid were selected and felled.Five disks measuring 3-cm in thickness were taken from the trunk at 4 m height.The sapwood was sampled from the whole disc between the transition and the inner bark tissues zones.Heartwood was sampled from 1 to 3 cm from the transition zone(Fig.1).Sapwood and heartwood tissues were separated from the desired region with a chisel and hammer,and the wood chips air-dried for 1 week or oven-dried for 2 days at 40°C before chemical analysis.

Fibre length was signi fi cantly different within and between species(Table 2).Interestingly,the hybrid of the two species showed signi fi cantly longer fi bres than both parents(Table 2).Among the parental species,A.auriculiformis(0.945±0.03)had signi fi cantly longer fi bre lengths compared to A.mangium(0.848±0.02),both in the sapwood and heartwood.Linear comparison analysis between different traits,i.e.,for lignin content,mean stem density and fi bre length for both sapwood and heartwood is summarized in Table 4.A positive and signi fi cantly high correlation was observed between sapwood and heartwood for all three traits.Linear relationship revealed that both sapwood and heartwood shared similar traits for lignin,mean stem density and fi bre length.However,correlation comparison among the three traits showed different levels of relationship.Generally,correlations between all traits,lignin content,mean stem density,and fi bre lengths for sapwood and heartwood were high and positively correlated,revealing that the transition wood was not different for these components(Table 4).Correlations between lignin in sapwood and heartwood were negative with mean stem density of the sapwood(-0.699,-0.719),and similarly with mean stem density in the heartwood(-0.202,-0.231)respectively(Table 4).Small but positive correlations were observed between mean stem densities of both sapwood and heartwood and fi bre length sapwood and heartwood(Table 4).The fi bre length of the Acacia hybrid was superior to that of the parental species.Sapwood tissues generally have longer fi bre lengths compared to heartwood tissues.Fibre length is positively correlated with diameter at breast height in poplars(Jiang et al.1994).Fibre length is an important trait because it has major effects on both yield and quality of pulp and wood products(Kim et al.2009;Macdonald and Hubert 2002).Wood with longer fi bre is associated with better tearing,burst and tensile strength in paper for greater pulp yields(Kim et al.2009;Macdonald and Hubert 2002).

经过管理后，观察组的不良事件发生率为护理安全事故7.41%（2例），护理纠纷为3.70%（1例），不良事件发生率为11.11%（3例）。对照组患者的不良事件发生率为护理安全事故14.81%（4例），护理纠纷为11.11%（3例），不良事件发生率为25.92%（7例）。两组结果对比，观察组的不良事件发生率明显低于对照组，差异有统计学意义（χ2=7.269，P=0.007）。

Fast-growing species have a signi fi cant impact on the quality of wood produced.The present study demonstrates that lignin content and mean stem density of these species vary greatly within different regions of the trunk.Hence,more replicates on mean stem densities and lignin content measurements were conducted to obtain a convergence value to represent the wood characteristics investigated.Fast-growing species have a high proportion of low density juvenile wood(Maeglin 1987).An imbalance in the proportion of low density juvenile wood in fast-growing species contributes to the imbalance in the lignin deposition across various sections of the trunk(Maeglin 1987).A.mangium is generally regarded as the species that gives lower pulp yields than A.auriculiformis and their hybrid.Ho et al.(1999)reported a loss of volume of about 7.5% of the total log volume due to heart rot.Higher amount of lignin content and wood defects in A.mangium warrant timely genetic improvement in order to improve the wood quality of this fast-growing species.The presence of low density juvenile wood is an undesirable property for both wood strength and pulp yield(Hai 2009).Imbalance in the proportion of low density juvenile wood raises concerns on the wood utility in timber from intensively managed forests compared to slow-growing species and mature natural stands(Zobel and van Buijtenen 1989).From an anatomical point of view,wood properties of a species greatly affect the pulp yield.The presence of large heart rot in A.mangium is an indicative of defective wood(Fig.1).Higher amounts of lignin and wood defects suggest thatgenetic improvement is needed to improve the wood quality of this fast-growing species.The presence of low density juvenile wood is an undesirable property for both wood strength and pulp yield(Hai 2009).Variation in wood properties(mean stem density,lignin and fi bre length)from pith to sapwood tissues in these Acacia species suggests more studies are needed in order to improve wood quality.It is interesting that lignin content is signi fi cantly and negatively correlated with mean stem density.Moreover,mean stem density is relatively easier to measure than lignin content,therefore selection for high mean stem density will be more ef fi cient to indirectly select for low lignin content.Interspeci fi c hybrids show better wood quality than parents and thus have a great potential for pulp production.Breeding Acacia hybrids with better tree form,disease resistance and low lignin content can help increase yield and quality of pulp(Asif et al.2016).The utilization of DNA markers can expedite the process of selecting superior hybrid genotypes from a breeding population(Asif et al.2015,2017).

Table 4 Pearson correlation coef fi cients between lignin,mean stem density and fi bre length traits

*Signi fi cantly different at≤0.05 level of signi fi cance

Lignin sapwood Fibre length heartwood Lignin sapwood 1 Lignin heartwood 0.981* 1 Mean stem density sapwood -0.699* -0.719* 1 Mean stem density heartwood -0.202 -0.231 0.705* 1 Fibre length sapwood -0.006 -0.165 0.198 0.15 1 Fibre length heartwood -0.012 -0.145 0.186 0.153 0.999* 1 Lignin heartwood Mean stem density sapwood Mean stem density heartwood Fibre length sapwood

Acknowledgements We wish to thank Dr.Koh Mok Poh,Puan Salamah Selamat and Puan Zaiton Saad for access to the Wood Chemistry Laboratory,Forest Research Institute Malaysia(FRIM)to conduct lignin analysis.

References

Asif MJ,Arif fi n M,Yit HM,Wong M,Abdullah MZ,Muhammad N,Ratnam W(2015)Utilization of STMS markers to verify admixture in clonal progenies of Acacia mapping populations and relabelling using assignment tests.J For Sci 61:200–209

Asif MJ,Cannon CH,Wickneswari R(2016)Cross-speci fi c amplifi cation of microsatellite DNA markers in Shorea platyclados(Dipterocarp).J For Res.doi:10.1007/s11676-015-0134-9

Asif MJ,Zaki MA,Norwati M,Wickneswari R(2017)Detecting mislabeling and identifying unique progeny in Acacia mapping population using SNP markers.J For Res.doi:10.1007/s11676-017-0405-8

Barnett JR,Jeronimidis G(1990)Wood quality and its biological basis.CRC Press,Boca Raton,p 224

Boerjan W,Ralph J,Baucher M(2003)Lignin biosynthesis.Annu Rev Plant Biol 54:519–546

Fagerstedt KV,Saranpa a P,Piispanen R(1998)Peroxidase activity isoenzymes and histological localisation in sapwood and heartwood of Scots pine Pinus sylvestris L.J For Res 3:43–47

Guendehou GHS,Lehtonen A,Moudachirou M,Ma kipa a R,Sinsin B(2012)Stem biomass and volume models of selected tropical tree species in West Africa southern forests.J For Sci 74(2):77–88

Hai PH(2009)Genetic improvement of plantation-grown Acacia auriculiformis for sawn timber production.Doctoral thesis,Swedish University of Agricultural Sciences,Uppsala

Hillman DC(2002)Single-species pulping:the world’s preferred market pulps.Solutions November 27–28

Ho KS,Hamdan H,Tan YE,Mohd SM(1999)Acacia mangium for timber and a case study of utilization.Paper presented at the 5th conference on forestry and forest products 1999 series,utilisation of plantation timber.Potential timber for the future FRIM,Sentang,p 9

Hu WJ,Harding SA,Lung J,Popko JL,Ralph J,Stokke DD,Tsai CJ,Chiang VL(1999)Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees.Nat Biotechnol 178:808–812

Huntley S,Ellis D,Gilbert M,Chapple C,Mans fi eld SD(2003)Signi fi cant increases in pulping ef fi ciency in C4HF5 transformed poplars:improved chemical savings and reduced environmental toxin.J Agric Food Chem 51:6178–6183

Jiang XM,Zhang LF,Zhang QW(1994)Genetic variation in basic wood properties of 36 clones of Populus deltoids.For Res 7:253–258

Kha LD(2001)Studies on the use of natural hybrids between Acacia mangium and Acacia auriculiformis in Vietnam.Agriculture Publishing House,Hanoi,p 171

Kim NT,Matsumura J,Oda K,Cuong NV(2009)Possibility of improvement in fundamental properties of wood of Acacia hybrids by arti fi cial hybridization.JWRS 55:8–12

Kirsten M,Myburg AA,De Leon JPG,Kirst ME,Scott J,Sederoff R(2004)Coordinated genetic regulation of growth and lignin revealed by quantitative trait locus analysis of cDNA microarray data in an interspeci fi c backcross of Eucalyptus.Plant Physiol 135:2368–2378

Kondo R,Tsutsumi Y,Imamura H(1987)Kinetics of β-aryl ether cleavage of phenoloic syringyl type model compounds.Holzforschung 41:83–87

Macdonald E,Hubert J(2002)A review of the effects of silviculture on timber quality of Sitka spruce.Forest 75:107–138

Maeglin R(1987)Juvenile wood tension wood and growth stress effects on processing hardwood.In:Proceedings of the 15th annual hardwood symposium of the Hardwood Research Council Memphis TN100-108

Malan FS,Male JR,Venter JSM(1994)Relationship between the properties of Eucalypt wood and some chemical pulp and paper properties.Pap S Afr 2:6–16

Malinen RO,Pisuttipiched S,Kohelmainen H,Kusuma FN(2006)Potential of Acacia species as pulpwood.Appita J 59:190–196

Pinto P,Evtuguin DV,Neto CP(2004)The chemistry of Eucalyptus globulus wood:pecularities and impact and bleaching behaviour.Congreso Iberoamericano De 492 Investigacion En Celulosa Y Papel

Qiu D,Wilson LW,Gan S,Washusen R,Moran GF,Southerton SG(2008)Gene expression in Eucalyptus branch wood with marked variation in cellulose micro fi bril orientation and lacking G-layers.New Phytol 179(1):94–103

Quang TH,Kien ND,Arnold SV,Jansson G,Thinh HH,Clapham D(2010)Relationship of wood composition to growth traits of selected open-pollinated families of Eucalyptus urophylla from a progeny trial in Vietnam.New For 39:301–312

Schoening AG,Johansson G(1965)Absorptiometric determination of acid-soluble lignin in semichemical bisul fi te pulps and in some woods and plants.Svensk Papperstid 68(18):607–613

Tsutsumi Y,Kondo R,Sakai K,Imamura H(1995)Difference in reactivity between syringyl and guaiacyl lignin in alkaline systems.Holzforschung 49:423–428

Wimmer R,Downes GM,Evans R(2002)High-resolution analysis of radial growth and mean stem density in Eucalyptus nitens grown under different regimes.Ann For Sci 59:519–524

Yamada N,Khoo KC,Yusoff Mohd Nor Mohd(1990)Sulphate pulping characteristics of Acacia hybrid Acacia mangium and Acacia auriculiformis from Sabah.J Trop For Sci 4:206–214

Yamashita S,Yoshida M,Takayama S,Okuyama T(2007)Stemrighting mechanism in gymnosperm trees deduced from limitations in compression wood development.Ann Bot 99:1–7

Yang J,Park S,Kamdem DP,Keathley DE,Retzel E,Paule C,Kapur V,Han KH(2003)Novel gene expression pro fi les de fi ne the metabolic and physiological processes characteristic of wood and its extractive formation in a hardwood tree species Robinia pseudoacacia.Plant Mol Biol 52:935–956

Zobel BJ,van Buijtenen JP(1989)Wood variation its causes and control.Springer,Berlin,p 363