Axial variations in anatomical properties and basic density of Eucalypturograndis hybrid(Eucalyptus grandis×E.urophylla) clones

S.K.Sharma•S.R.Shukla•S.Shashikala•V.Sri Poornima

Axial variations in anatomical properties and basic density of Eucalypturograndis hybrid(Eucalyptus grandis×E.urophylla) clones

S.K.Sharma1•S.R.Shukla1•S.Shashikala1•V.Sri Poornima1

We studied two clones of Eucalypt urograndis hybrid(Eucalyptus grandis×E.urophylla),GR283 and GR330,grown in Tumkurdistrictof Karnataka(India),and felled 5–6 years old three trees ofeach clone.We recorded axial variations in heartwood content,bark properties, wood density and anatomical characteristics of wood including fibre length,fibre diameter,fibre wall thickness, lumen diameter,vessel frequency,vessel diameter and vessel element length.Clone GR283 had about 10% heartwood,significantly lower than for clone GR330 (37%).Basic wood density along the tree height varied significantly within and between the clones.We observed significant variations in fibre length,fibre diameter and wall thickness within and between the two clones.Vessel frequency and vesselelementlength did notvary butvessel diameter differed significantly between the clones.With a greater proportion of sapwood,clone GR283 can be utilized for paper and pulp applications.Clone GR330 had a higher proportion of heartwood and lower wood density and,hence,is more suitable for light-weight material applications.

Eucalypt urograndis hybrid(Eucalyptus grandis×E.urophylla)·Fibre characteristics·Vessel characteristics·Wood density·Bark density

Introduction

Eucalyptspecies,predominantly the Australian E.grandis Hill Ex.Maiden,have been planted extensively in the tropics.The fast growth of eucalypts and the increased demand for wood and wood products has led to steady increase in the extent of these plantations(Bennett 2010). The existing plantations are promising,growth is fast and the wood is of quality suitable for industrial use.With the introduction of a genetic improvement program,many other eucalypt species,their hybrids and clones,besides E. grandis,have been planted in provenance trials aimed at improving growth rate as well as pulp wood characters, including density and fibre characteristics(Loulidi et al. 2012).Recently,these hybrids are used extensively in commercial plantations,mostly in clonal forestry(Gominho et al.2001).One hybrid E.grandis×E.urophylla, commercially known as Eucalypt urograndis,provides a significant share of global eucalypt pulpwood supply.This species aims at combining the growth characteristics of E. grandis with an increase in wood density and fibre properties of E.urophylla(Quilho et al.2006).

Basic density is generally taken as one of the major wood quality parameters in tree improvement programs (Lima etal.2000).Wood properties of differentspecies are known to vary atdifferentheights of a tree with no definite trend of variation(Gominho et al.2001;Shashikala and Rao 2009).We evaluated vertical variation of different properties to observe the extent of variability in the properties due to the juvenile nature of wood.Fibre characteristics of important eucalypt pulpwood species were reported by Jorge et al.(2000),Miranda et al.(2001a, 2003),and Rao etal.(2002).Variation in basic density and fibre characteristics of E.grandis and E.urophylla were also reported(Quilho and Pereira 2001;Quilho etal.2006).Limited information is available about the variations in density and anatomical properties of E.grandis×E. urophylla hybrid clones(Gominho et al.2001;Grzeskowiak et al.2000;Quilho et al.2006).Few studies have characterized the anatomical properties of E.urophylla plantations grown in India.We therefore undertook studies ofthe basic density and anatomicalproperties,such as fibre and vessel morphology to identify within and between variations in the clones of E.urograndis hybrid(E.grandis×E.urophylla)grown in Tumkur,Karnataka,India. Information generated on the variability of these properties will be helpful in evaluating the usefulness of these clones for pulp wood and solid wood product applications.

Materials and methods

A total of 6 ramets,three from each of the two E.urograndis hybrid clones GR283 and GR330,were selected for this study.Ramets are genetically identical individuals in a group of clones.The ramets were procured from Grasim Polyfibres,Karnataka,India.The clones GR283 and GR330 are henceforth referred as clone A and clone B, respectively.The clones were raised at a spacing of 3×3 m in Tumkur district(77°08′E and 13°20′N)of Karnataka under rainfed condition.The clones were 5–6 years old at the time of harvesting.The length of the felled trees was measured with a measuring tape and stump height was added to get the total height of the tree.Total height was in the range of 16–18 m for both clones.From each tree,six billets(each 2 m in length)were obtained by cutting the tree at six different heights(2,4,6,8,10 and 12 m)along the stem from the base.The girth of different billets was in the range of29.0–39.5 and 28.0–36.5 cm for clone A and clone B,respectively.Girth was measured using a tape atthree positions(bottom,middle and top)and the average value was reported as the girth of each billet.

Two discs were cut from each billet.The first disc was used to determine the heartwood percentage and basic density.To estimate heartwood percentage,the total diameter and heartwood diameter of discs were measured in four directions.Total area of the disc and heartwood portion was calculated separately and heartwood percentage was calculated using the ratio of area of the heartwood portion to the totalarea of the disc.The disc was debarked and the bark thickness was measured using calipers(accuracy 0.01 mm),and the bark samples were immersed in water to saturation.Six sample blocks(each of 1 cm3)were cut from the disc and were kept in water until fully saturated.The basic density of wood and bark was calculated using oven-dry weight and green volume(Anon. 1986).From the second disc,three samples representing pith(5 mm from pith),middle and near bark regions were taken from the sector for maceration.Slivers obtained from these three samples were pooled and macerated with 30% HNO3and a few crystals of potassium chlorate(KClO3) and heated until the slivers became colorless.The mixture was then washed with distilled water to leach out the acid (Jane 1970).The macerated material was used for measuring fibre and vessel characteristics.Forty unbroken fibres were used for length and diameter measurements. Double-wall thickness was calculated by deducting lumen diameter from fibre diameter.Vessel element length and vessel diameter were also measured from the macerated material.A Leica(Model Laborlux-S POL)microscope with Image Analysis software(QWin Standard)was used for these measurements.Vessel frequency was measured from the entire length of the sector using a stereozoom microscope(Model Leica S8 APO)after exposing its cross surface.For measuring vessel frequency,a wedge was cut from the discs taken from different heights and cross sectional surface from pith to bark was exposed with a sharp knife.The exposed surface was then observed under the stereozoom microscope.A field of 1 mm2grid area was used to measure vessel frequency.The entire length of the sector/wedge of the sample was observed at12 fields from pith to bark,and the vessels thatappeared completely in the grid were recorded.The average of 12 such fields was taken as vesselfrequency.

Runkel ratio and shape factor were determined using following formulae:

where w is the fibre wallthickness,fd is the fibre diameter and ld is the lumen diameter.

Statisticalanalysis was conducted using SigmaStat(Ver. 3.5,Systat Software Inc.,2006).ANOVA and Fisher LSD were used for multiple comparisons.

Results and discussion

Heartwood had a distinctreddish pink colorand was easily distinguishable from sapwood.Heartwood percentages varied from 1 to 21%in clone A and 33 to 48%in clone B along the tree height,and were greatestatthe base of the tree.The decrease in percentage of heartwood from the base to the top of the tree was reported for several eucalypts,e.g.,E.tereticornis and E.grandis(Pillaietal.2013), E.globulus(Gominho and Pereira 2000),E.urograndis hybrid(Gominho etal.2001)and E.citriodora(Shashikala et al.2009).Heartwood percentage generally varies with age,site and growth rate of the trees(Wilkins 1991).Heartwood ofa tree is preferred forvarious products due to its darker color and higher resistance to attack by various wood deteriorating agencies(Taylor et al.2002).

Variation of wood density,bark thickness and bark density at different sampling heights for both clones is shown in Table 1.Wood density ranged from 538 to 571 and 420 to 464 kg m-3in clone A and clone B,respectively.Quilho et al.(2006)reported wood density as 491 kg m-3in 5½-year-old trees of E.urograndis hybrid in Brazil,which approximates the wood density recorded for clone B in our study.Higher values were observed in clone A(552 kg m-3),exceeding the value of 543 kg m-3reported by Bassa(2002)for 7-year-old trees of E.grandis×E.urophylla clone.The values were found to be comparable to the wood density(492–600 kg m-3)of 9-year-old trees E.globulus(Miranda etal.2001b).Itmay be seen from Table 1 that both wood and bark of clone A exhibited higher density than clone B.According to Ikemori et al.(1986),the wood density requirement of the pulp industry is in the range of 480–570 kg m-3and, hence,clone A proved best suited for this purpose.The basic density for E.grandis was reported as 442 kg m-3in 7-year-old trees(Githiomiand Kariuki2010)and thatof E. urophylla as 510 kg m-3for 6-year-old trees(Vale et al. 2002).Although,the increase in wood density with tree height is reported as a general trend in Eucalypts(Quilho and Pereira 2001),no definite trend was observed from base to top ofthe trees in the presentstudy.However,wood density of clone A(552±17,n=48)was significantly greater(p＜0.05)than thatof clone B(441±20,n=48) which may impact the overall utilization of clone A.

Bark thickness ranged from 2.2 to 5.7 mm in clone A (avg.3.2 mm)and 1.8 to 5.3 mm(avg.3.1 mm)in clone B. The trend ofdecrease in bark thickness with increasing tree height was in concurrence with Quilho and Pereira(2001) for E.globulus and Shashikala et al.(2009)for E.citriodora.Bark density ranged from 390 to 424 kg m-3in clone A and 335 to 401 kg m-3in clone B with an average of 402 kg m-3in clone A and 354 kg m-3in clone B. Bark of clone A was significantly(p＜0.001)more dense (402±16,n=18)than bark of clone B(354±39, n=18).Wide variations in bark density were also reported for E.globulus depending on site conditions(Quilho and Pereira 2001).

The average values of fibre length,fibre diameter,fibre wall thickness and lumen diameter of both the clones at 6 sampling heights are shown in Table 2.Average fibre length ranged from 0.91 to 1.02 and 0.96 to 1.14 mm in clone A and clone B,respectively.These ranges were similar to others reported in the literature,viz. 0.82–1.04 mm for seed origin and 1.01–1.11 in 5½year old clones(Quilho et al.2006),1.08 mm(Carvalho and Nahuz 2001)and 0.81 mm for 7-year-old E.grandis×E. urophylla hybrid(Grzeskowiak et al.2000).

Our study showed ranges of fibre length similar to other reports for eucalypts,e.g.,0.85 and 0.94 mm in 4½-yearold E.tereticornis(Rao et al.2002),0.82–0.93 mm in 7-year-old E.grandis×E.camaldulensis(Grzeskowiak et al.2000)and 0.81,1.03,and 1.15 mm for one of the parent trees,i.e.E.grandis of 3,5 and 9-year-old trees (Bhat et al.1990).A small axial variation of fibre length decreasing with tree height was in conformation with reports for E.globulus(Jorge et al.2000),E.grandis(Bhat et al.1990),and E.urograndis hybrid(Quilho etal.2006). Average fibre diameter ranged from 14.3 to 16.0μm in clone A and 14.3 to 16.8μm in clone B.The fibre wallthickness ranged from 4.0 to 6.1 and 4.8 to 6.1μm in clone A and B,respectively.

Table 1 Average values ofwood density,bark thicknessand bark density forclone A and clone B

Table 2 Average values of fibre length,fibre diameter,fibre wall thickness and lumen diameter of clone A and clone B by sampling height

Table 3 Average vessel frequency,vessel diameter and vessel element length of clone A and clone B by sampling height

The fibre diameter and wallthickness for E.urograndis clones as reported by other studies were 20μm and 3.9–4.8μm,respectively for 5½-year-old clone(Quilho et al.2006),and 17.1 and 4.2μm(Carvalho and Nahuz 2001).Grzeskowiak et al.(2000)reported the range of 12–18μm for fibre diameter and 2.4–2.6μm for fibre wall thickness in 7-year-old clones.The fibre diametervalues in our study(15.2–15.7μm;Table 2)were comparable to the values of14.5–16.9μm as reported by Rao etal.(2002)for 4½-year-old E.tereticornis clones.

Fibre length,fibre diameter and fibre wall thickness varied significantly with tree height for both clones.These parameters also varied significantly between clones.Most of the fibre parameters showed maximum values at 8 m from the ground(Table 2).

Fibre characteristics are collectively represented by Runkel ratio and shape factor.Runkel ratio less than 1 indicates suitability for paper production because fibers are more flexible,readily collapse and form a paper with large bonded area(Sharma et al.2013).Pande et al. (2008)reported that fibres with lower values of shape factor,Runkelratio and density willyield stronger paper. Runkel ratio and shape factor were 0.50 and 0.55,respectively,for clone A and 0.38 and 0.41,respectively for clone B,indicating suitability for production of strong paper.

Table 3 lists the average values of vessel frequency, vessel diameter and vesselelementlength for clones A and B by trunk height.Vessel element length,vessel diameter and vessel frequency were 272–393,149–185μm and 12–13 mm-2,respectively,for clone A,and 303–380, 129–188μm and 11–14 mm-2,respectively,for clone B. Dadswell(1972)reported average vesselelementlength of 430μm,vessel diameter of 155μm and vessel frequency as 6 mm-2forone ofthe parentspecies i.e.E.grandis.Rao et al.(2003)reported vessel element length,vessel diameter and vessel frequency as 334–378μm,138–152μm and 13–17 mm-2,respectively,for 6-to 7-year-old E. tereticornis clones.Exceptfor vesselfrequency in clone A, other vessel parameters differed significantly by stem height.No statistically significantdifference was observed between clones A and B forvesselelementlength orvessel frequency,whereas vesseldiameterforclone A(167±33, n=240)was significantly larger(p＜0.001)than clone B (155±32,n=240).

Conclusion

Axial variations in basic wood density and most of the anatomicalparameters were recorded in both clones.Clone GR283 had less heartwood than clone GR330.Basic wood density varied significantly within(axial)and between clones.Significant variation was recorded in fibre length, fibre diameter and wall thickness within and between the clones.Vesselfrequency and vesselelementlength did not show any significant variation,whereas,vessel diameter varied significantly between clones.Clone GR283 with comparatively more sapwood proved suitable forpaperand pulp applications,whereas,clone GR330 with a greater proportion ofheartwood and lower density was suitable for applications where light-weight material is required.

AcknowledgmentsThe authors are thankful to the Director and Group Coordinator(Research),Institute of Wood Science and Technology,Bangalore for their keen interest and encouragement given during the project work.Thanks are also due to Dr.V.P.Tewari,Scientist,Institute of Wood Science and Technology,Bangalore for his help in carrying outstatistical analysis.

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27 November 2012/Accepted:27 March 2014/Published online:15 May 2015

©Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2015

The online version is available at http://www.springerlink.com

Corresponding editor:Yu Lei

✉S.K.Sharma sksharma@icfre.org

1Wood Properties and Engineered Wood Division,Institute of Wood Science and Technology,P.O.Malleswaram, Bangalore 560 003,India