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WOOD RESEARCH 55 (3): 2010 25-36

EFFECT OF CAMBIUM AGE AND RING WIDTH

ON DENSITY AND FIBRE LENGTH OF BLACK LOCUST

AND CHESTNUT WOOD

Stergios AdamopoulosTechnological Educational Institute of Larissa, Department of Forestry

and Management of Natural Environment, Karditsa, Greece

Marina Chavenetidou, Costas Passialis, Elias VoulgaridisAristotle University of Thessaloniki

School of Forestry and Natural Environment,Laboratory of Forest Utilization,

Thessaloniki, Greece

ABSTRACT

The relationship between wood density (WD) and fibre length (FL) with cambium age (CA) and ring width (RW) was studied in two ring-porous species, black locust and coppice-grown chestnut, collected in the Sithonia Peninsula, Chalkidiki, Greece. Using regression analysis methods, models of WD and FL in relation to CA and RW were obtained. It was found that the effect of CA and RW on WD and FL was similar for both species examined. WD of black locust and chestnut was predicted better through a model using CA and RW. A model for FL variations was also obtained with CA and RW and was more accurate than the simple models based on the two factors, CA and RW, separately. The multiple regression models suggested that the use of cambial age of growth rings together with their width might explain better their effects on WD and FL of black locust and chestnut.

KEY WORDS: wood density, fibre length, cambium age, ring width, black locust, chestnut

INTRODUCTION

Cambium age and growth rate are main factors affecting wood properties, primarily cell dimensions and density in both coniferous and deciduous species. Reports on variation patterns of wood density and cell dimensions with age are associated with the process of cambium maturation and the assessment of the period of juvenile tree development. The majority of these studies refer chiefly to conifers while comparatively less attention has been paid to hardwoods, particularly ring-porous (Dinwoodie 1961, Panshin and de Zeeuw 1980, Zobel and van Buijtenen 1989, Saranpää

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WOOD RESEARCH

2003). In some ring-porous hardwoods, such as Quercus, Celtis and Fraxinus species, higher wood

density was observed near the pith (Hamilton 1961, Taylor 1971, Taylor 1979, Wheeler 1987). Fraxinus americana was reported to exhibit a decrease or a consistency of wood density moving in a radial direction from pith to bark (Paul 1963, Quanci 1988). In Carya illinoensis and C. tomentosa species, wood density increases linearly from the pith outward to the bark (Taylor 1969, Taylor 1979). In Carya ovata and Quercus nigra, wood density also increases from pith to bark but in a curvilinear pattern, dropping off slightly in the outermost mature wood (Taylor 1979).

Numerous publications on radial variation of fibre length in ring-porous hardwoods as reviewed by Dinwoodie (1961) reported that fibres are shortest near the pith. A common variation pattern is a rapid increase in fibre length during the first years, followed by a more gradual increase until a maximum is reached. This was shown in Carya, Celtis, Quercus and Tectona grandis species (Knigge and Koltzenburg 1965, Taylor 1971, Berchem et al. 1972, Taylor and Wooten 1973, Taylor 1979). For Fraxinus and Quercus robur, it has been reported as a pattern of a continuous increase in fibre length outward from the pith to bark (Bosshard 1951, Hamilton 1961, Saucier and Hamilton 1967, Denne and Whitbread 1978).

Ring width variation with age is a potential source of wood property variation. Ring width in forest trees usually follows a general pattern of decrease as age increases as a result of stand competition while deviations might occur due to soil and climatic conditions (Zobel and Sprague 1998). In ring-porous hardwoods, growth rate, which is expressed by ring width, is positively correlated to wood density and is attributed to the fact that earlywood zone is nearly constant from year to year and the wider rings therefore contain more dense latewood with fewer vessels (Panshin and de Zeeuw 1980, Wheeler 1987). Nevertheless, other workers failed to find any relationship between ring width and wood density (van Eck and Woessner 1964, Taylor and Wooten 1973, Taylor 1977). A possible reason could be that the earlywood/ latewood proportion, the percentage of cell wall material and the tissue proportions differ between the annual rings, especially between juvenile and mature wood (Zhang and Zhong 1992).

It is less clear how fibre length is affected by growth rate in ring-porous hardwoods. Zobel and van Buijtenen (1989), summarizing the relation of cell length to growth rate in hardwoods, conclude that faster growing trees usually have shorter fibres. For ring-porous hardwoods, this was verified only for Celtis (Taylor and Wooten 1973) while Denne and Whitbread (1978) found no relationship between growth rate and fibre length in Fraxinus.

Studying the independent effects of ring width and age on wood properties may lead to false results due to the tendency of the two factors to naturally confound one another. Ring width is highly variable as it is controlled by a variety of factors such as environmental fluctuations and competition for resources. The age of the cambium at the time of formation of growth increment is also essential to wood properties (Panshin and de Zeeuw 1980, Zobel and van Buijtenen 1989). Wood property differences are partly the result of age effects (e.g. juvenile wood, mature wood). In that perspective, the age influence must be accounted for in some manner. The combined effect of cambium age and growth rate on wood properties has been investigated only for diffuse-porous hardwoods by Liu and Bao (2001). They modelled fibre length, microfibril angle and wood density in relation to cambium age and growth rate in plantation poplar clones in China. It was revealed that only fibre length could be well predicted when using cambium age and ring width.

The objective of this research was to study the effect of cambium age and growth rate on wood density and fibre length in two ring-porous hardwoods: black locust and coppice-grown chestnut. The possibility of predicting wood density and fibre length in the species by using cambium age and growth rate was also explored. The species are normally harvested in relatively short rotations

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(30 and 40 years on average for coppice-grown chestnut and black locust respectively) and are of commercial importance in the Mediterranean region for furniture, flooring and construction purposes.

MATERIAL AND METHODS

The material for this study was collected from the Sithonia Peninsula, Chalkidiki, Greece. Three black locust (Robinia pseudoacacia L.) trees and five chestnut (Castanea sativa Mill.) coppice-trees were chosen with minimal lean, relatively straight stems and no major external defects. The black locust trees were 35-37 years and had a diameter at ground level of 18.1-27.7 cm, while age and diameter at ground level for the chestnut trees was 25-27 years and 19.1-24.0 cm respectively.

From each tree a 2 cm thick disc was cut at the base (0.30 m above ground level) and seasoned at laboratory conditions (20 °C, 55 % RH). A pith-to-bark strip about 2 cm tangentially and 1.5 cm longitudinally was prepared along an average radius from each disc. This strip was subsequently divided into two strips. One strip (about 1 cm wide and 1.5 cm thick) was used to assess ring width and oven-dry density and the other to measure fiber length.

For the measurement of growth rate (annual ring width) from pith to bark, the radial wood strips were smoothed with sandpaper on their transverse surfaces. The measurement of annual ring width was performed using a digital positionmeter to the nearest 0.01 mm. The strips were then split carefully into pieces of individual rings. In case of very narrow annual rings, the radial strips for oven-dry density measurements were divided into 2-5 annual rings depending on the degree of uniformity of adjacent annual ring widths. Dry volume of all pieces was measured by the water displacement method.

The strips for the measurement of fibre length were split into individual rings, from which matchstick-sized subsamples were cut with a razor blade. The subsamples were macerated by warming in glacial acetic acid and 30 % hydrogen peroxide (v:v) at 60 °C for 24 h. After washing with water several times macerated elements were transferred to a clean slide. Lengths of eighty randomly selected unbroken fibres per annual ring were measured with a light microscope equipped with an image analysis system.

RESULTS AND DISCUSSION

Ring width versus cambium ageRing width is often considered as a useful predictor of some wood properties (e.g. density, mechanical strength). The patterns of ring width (RW) variation with age of black locust and chestnut trees are shown in Fig. 1. Ring width increased in all black locust trees within the first 6-9 growth rings from the pith and then gradually decreased. In the chestnut trees ring width gradually decreased with increasing tree age.

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WOOD RESEARCH

Fig. 1: RW variations with CA of black locust and chestnut trees

Wood densityLinear models of wood density (WD) with cambium age (CA) and ring width (RW) are shown in Fig. 2. The regression equations of first order degree are:

WD = A1 + A2CA (1)

and

WD = B1 + B2RW (2)

where A1, A2, B1, B2 are coefficients.

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Fig. 2: WD as a function of CA (up) and RW (down) in black locust and chestnut

WD was not related to CA as it was found to be more or less uniform from pith to bark (respective r values for black locust and chestnut were 0.083 and 0.081). Regarding the effects of age on wood density of black locust, these results were consistent with the results reported by Voulgaridis et al. (2000). Dry wood density of mature black locust trees aged 18-39 years from Bulgaria, Greece and Hungary was found to be constant from pith to bark with slight deviations in the first and the last annual rings. Another study (Stringer and Olson 1987) showed that wood density of 10 to 12 year-old black locust trees increased from the pith to the 8th radial increment and remained relatively unchanged beyond that point. The radial pattern of wood density variation in chestnut coppice trees aged 20 years was characterized by a decrease to ring number 4-6 from the pith, an increase around ring 8-10 and fluctuations after that point towards the periphery (Fioravanti 1995).

WD had a significant positive linear correlation at the 0.01 level with RW in both species. However, correlations could not be characterised as strong (r = 0.563 for black locust and r = 0.234 for chestnut). Positive dependence of dry wood density and ring width was also found for black locust wood from clones aged 8 years (Klašnja and Kopitovič 1995). Other works showed inconsistent correlations between wood density and ring width in black locust. Kopitovič et al. (1989) did not find any relationship between wood density and width of growth rings in black locust trees aged 26 years. The same observation has also been done for young black locust wood aged 10 years (Klašnja and Kopitovič 1992). No significant correlation was found between ring width and density in chestnut by Chanson (1988) and Fioravanti (1995). The previous relationships suggested that WD cannot be predicted well when CA or RW are used in separate models. Models (1) and (2) were used in order to obtain a multiple linear regression model. The statistical analyses were executed with the SPSS for Windows 14.0 software. The model had the following structure:

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WOOD RESEARCH

WD = C1 + C2CA + C3RW +C4CA*RW (3)

where C1, C2, C3, C4 are coefficients.

Using equation (3), WD of all black locust and chestnut trees was modeled in relation to CA and RW (Tab. 1).

Tab. 1: Parameter and coefficient of model of WD varied with CA and RW in black locust and chestnut

Tree No C1 C2 C3 C4 r F value Observation No

123

General

Black locust0.51410.73800.54040.5848

0.0011-0.01000.00710.0010

0.0205-0.02270.03800.0220

0.00380.0047-0.00140.0006

0.9060.9650.9240.698

6.109 ns

22.241*9.798*6.971*

89926

12345

General

Chestnut0.51250.63290.59830.61300.64950.5792

0.0005-0.00500.0007-0.0036-0.0067-0.0025

0.0106-0.0168-0.0038-0.0036-0.0084-0.0004

0.00030.00220.00010.00130.00270.0015

0.5620.5670.5150.6150.8770.462

3.383*3.466*2.767ns

4.451*23.353*11.400*

2626272625130

r correlation coefficient* significant at the 0.05 levelns not significant at the 0.05 level

According to Tab. 1, the model was significant (ANOVA, P = 5 %) in most of the trees with the exception of tree No.1 for black locust and tree No. 3 for chestnut. The correlation coefficients were very high for the two black locust trees and quite high for the four chestnut trees varying from 0.924 to 0.965 and from 0.562 to 0.877 respectively. WD of black locust (WDBL) and chestnut (WDC) in relation to CA and RW can be predicted significantly (F = 6.971, P = 5 %, observation number 26 for black locust and F = 11.400, P = 5 %, observation number 130 for chestnut) by the general models:

WDBL = 0.5848 + 0.0010CA + 0.0220RW + 0.0006CA*RW (4)

WDC = 0.5792 - 0.0025CA - 0.0004RW + 0.0015CA*RW (5)

Both Eqs. 4 and 5 could model WD changed with CA and RW in black locust (r = 0.698) and chestnut (r = 0.462) better than the simple model (Eq. 2) using RW only (respective correlation coefficients 0.563 and 0.234).

Fibre lengthFig. 3 presents fibre length (FL) as a function of CA. The course of this dependence was

accurately approximated (0.05 level according to t-test) by the logarithmic regression:

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FL = D1 + D2Ln(CA) (6)

where D1, D2 are coefficients.

In both black locust and chestnut, FL clearly increased from the pith to the growth rings of a certain age. In the rings further from that point, FL remained more or less constant. The results are consistent with those published for black locust wood. Voulgaridis et al. (2000) found typical radial variability curves for fibre length in mature black locust trees of different origin (Bulgaria, Greece, Hungary). Fibre length varied progressively and rapidly in the first 8-13 growth rings and then attained a typical level. In young black locust trees (8-12 years old), a significant radial increase in fibre length has been reported (Furukawa et al. 1983, Stringer and Olson 1987). Age effects on cell dimensions of chestnut wood have only been reported for vessel elements (Fioravanti 1995).

The linear regression analyses revealed significant correlations between FL and RW at the 0.05 level according to t-test and, therefore, FL of black locust and chestnut can be calculated using RW by the function:

FL = E1 + E2RW (7)

where E1, E2 are coefficients.

However, the low correlation coefficients indicated that Eq. 7 could explain only little of FL variation in black locust and chestnut (Fig. 3). The negative correlation of RW with FL (Fig. 3) was in agreement with a previous study by Klašnja and Kopitovič (1992) for black locust wood from young stands (10 years old).

Fig. 3: FL as a function of CA (up) and RW (down) in black locust and chestnut

Fibr

e

Fibr

e

Fibr

e

Fibr

e

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Using the same methodology as for WD, a multiple linear regression model of FL in relation to CA and RW was developed by the Eqs. 6 and 7:

FL = F1 + F2Ln(CA) + F3RW + F4Ln(CA)*RW (8)

where F1, F2, F3, F4 are coefficients.

FL of all black locust and chestnut trees was then regressed using the combined model (Eq. 8) and the results are shown in Tab. 2. According to ANOVA, the regression result was significant at the 0.05 level for all trees while the correlation coefficients were very high and ranged from 0.945 to 0.973 for black locust and from 0.941 to 0.983 for chestnut. By putting together all the data of the black locust trees, a general model (F = 213.029, significant at P = 5%, 108 observations) for fibre length of black locust (FLBL) was derived as follows:

FLBL = 0.5170 + 0.1480Ln(CA) + 0.0283RW – 0.0091Ln(CA)*RW (9)

Similarly, the following general model could significantly (F = 72.433, P= 5 %, 130 observations) predict fibre length (FLC) variations with cambium age and ring width for chestnut:

FLC = 0.8160 + 0.0865Ln(CA) – 0.0066RW + 0.0110Ln(CA)*RW (10)

A comparison of the correlation coefficients showed that the prediction of fibre length in black locust and chestnut using the multiple regression models (Eqs. 9 and 10) is more accurate than using the simple logarithmic model based on cambium age (Eq. 6 and Fig. 3). Significant improvements in predicting fibre length of each tree were achieved if the multiple regression model was used (r = 0.945 to 0.973 for black locust trees and r = 0.941 to 0.983 for chestnut trees) instead of the logarithmic one (r = 0.920 for black locust and r = 0.776 for chestnut). The combination of CA and RW could describe 86% and approximately 63% of the total fibre length variation in black locust and chestnut respectively (Tab. 2).

Tab. 2: Parameter and coefficient of model of FL varied with CA and RW in black locust and chestnutTree No F1 F2 F3 F4 r F value Observation No

123

General

Black locust0.59410.56460.52950.5170

0.10010.14040.13150.1480

-0.00910.01130.00610.0283

0.0152-0.0014-0.0007-0.0091

0.9450.9730.9690.927

85.912*190.653*168.618*213.029*

353637108

12345

General

Chestnut0.71410.99530.98270.67120.67750.8160

0.08440.04650.04380.14770.14320.0865

0.0100-0.0326-0.04490.03280.0163-0.0066

0.00160.01930.0263-0.00680.00130.0110

0.9410.9830.9710.9650.9750.796

56.280*214.507*124.257*98.365*136.592*72.433*

2626272625130

r correlation coefficient* significant at the 0.05 level

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CONCLUSIONS

Relationships among cambium age (CA), ring width (RW), fibre length (FL) and wood density (WD) observed in this study were alike for the two ring-porous hardwoods, black locust and chestnut. The results indicated that not only CA but also RW should be considered when estimating FL and WD. WD changes with CA and RW can be significantly modelled using regression analysis in both species while this property is poorly correlated with the two factors separately. Similarly, a multiple regression model incorporating CA and RW is a very good predictor of FL which further improves the FL-age relationship in the two species.

REFERENCES

1. Berchem, T. E., Moslemi, A. A., Sutula, P. R., 1972: Fiber length in the wood of tree-of-heaven. Wood and Fiber 4(3): 234-235

2. Bosshard, H. H., 1951 : Variabilität der Elemente des Eschenholzes in Function von der Kambium-tätigkeit. Schweiz Z. Forstwesen 102: 648-665

3. Chanson, B., 1988 : Etude de la variabilité de quelques propriétés physiques et anatomiques du bois de Châtaignier (Castanea sativa Mill.). Application à l'étude de la roulure. Thèse de Docteur en Physiologie, Biologie des Organismes et des populations de l'Université Montpellier 2, Botanique

4. Denne, M. P., Whitbread, V., 1978: Variation of fibre length within trees of Fraxinus excelsior. Canadian Journal of Forest Research 8(2): 253-260

5. Dinwoodie. J. M., 1961: Tracheid and fiber length in timber – a review of literature. Forestry 34: 125-144

6. Fioravanti, M., 1995: Nature and occurrence of juvenile wood in chestnut (Castanea sativa Mill.) stems from coppice forest. Forêt Méditerranéenne 16(1): 58-66

7. Furukawa, I., Nakayama, T., Sakuno, T., Kishimoto, J., 1983: Wood quality of small hardwoods. 3. Horizontal variations in the length of fibers and vessel elements in trees with storeyed and non-storeyed wood (Robinia pseudoacacia, Diosphyros kaki, Tilia japonica, Alnus hirsula). Bulletin Faculty Agriculture Tottori University 35: 42-49

8. Hamilton, J. R. 1961: Variation of wood properties in southern red oak. Forest Products Journal 11: 267-271

9. Klašnja, B., Kopitovič, S., 1992: Some properties of robinia wood obtained from trees grown in provenance field experiments. Drevarsky Vyskum 37: 1-8

10. Klašnja, B., Kopitovič, S., 1995: Parallel examination of some characteristics of young robinia wood. Drevarsky vyskum - Wood Research 40: 1-9

11. Kopitovič, S., Klašnja, B., Guzina, V., 1989: Importance of structural, physical and chemical properties of Robinia wood (Robinia pseudoacacia L.) for its mechanical characteristics. Drevarsky Vyskum 34: 13-30

12. Knigge, W., Koltzenburg, C., 1965: The influence of timber qualities and ecological conditions on the cell sizes and on the proportions of types of cell in hardwoods in the temperate zones. In: Proceedings IUFRO, Vol. 2, Melbourne, 24 pp.

13. Liu, S., Bao, F., 2001: Modeling wood properties in relation to cambium age and growth rate in plantation poplar in China. Journal of Institute of Wood Science 15(5): 247-252

14. Panshin, A. J., de Zeeuw, C., 1980: Textbook of wood technology. 4th Ed, McGraw-Hill. New York, 722 pp.

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15. Paul, B. H., 1963: The application of silviculture in controlling the specific gravity of wood. Tech. Bull. No 1288, USDA For. Serv., Washington, DC, 97 pp.

16. Quanci, M. J., 1988: Mechanical and anatomical properties of short rotation Douglas-fir and white ash. MS thesis, Dept. of Forestry and Natural Resources, Purdue Univ., West Lafayette, Ind

17. Saranpää, P., 2003: Wood density and growth. In: Wood quality and its biological basis. Blackwell & CRC Press, London & Boca Raton, FL. Biological Sciences Series Pp. 87-117

18. Saucier, J. R., Hamilton J. R., 1967: Within-tree variation of fiber dimensions in green ash. Georgia Forest Res. Pap. No 45, Southeastern Forest Expt. Sta., Athens, GA. 6 p

19. Stringer, J. W., Olson, J. R., 1987: Radial and vertical variations in stem properties of juvenile black locust (Robinia pseudoacacia). Wood and Fiber Science 19(1): 59-67

20. Taylor, F. W., 1969: Variation in wood properties in pecan. For. Prod. Utiliz. Lab. Mississipi State Univ. Res. Pap. 11. 17 pp.

21. Taylor, F. W., 1971: Variation of wood properties in sugarberry. For. Prod. Utiliz. Lab. Mississipi State Univ. Res. Pap. 11. 17 pp.

22. Taylor, F. W., 1977: Variation in specific gravity and fiber length of selected hardwoods throughout the Mid-South. Forest Science 23: 190-194

23. Taylor, F. W., 1979: Property variation within stems of selected hardwoods growing in the Mid-South. Wood Science 11(3): 193-199

24. Taylor, F.W., Wooten, T.E., 1973: Wood property variation of Mississipi Delta hardwoods. Wood and Fiber 5(1): 2-13

25. Van Eck, W. A., Woessner, R. A., 1964: A study of wood density in yellow poplar and red oak as related to environment. West Virginia Acad. Sci. 36. 8 pp.

26. Voulgaridis, E., Passialis, C., Adamopoulos, S., 2000: Wood quality characterization in black locust of different origin. In: Proceedings of the 3rd Workshop of COST Action E10 “Measuring of wood properties, grades and qualities in the conversion chains and global wood optimization”, June 19-21, 2001, Espoo, Finland, Pp. 147-162

27. Wheeler, E. A., 1987: Anatomical and biological properties of juvenile wood in conifers and hardwoods. 41st Ann Meet FPRS Louisville, Kentucky

28. Zhang, S. Y., Zhong, Y., 1992: Structure-property relationship of wood in East-Liaoning oak. Wood Science and Technology 26: 139-149

29. Zobel, B. J., van Buijtenen, J. P., 1989: Wood variation-its causes and control. Springer-Verlag. New York, 363 pp.

30. Zobel, B. J., Sprague, J. R., 1998: Juvenile wood in forest trees. Springer-Verlag. New York, 300 pp.

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Stergios AdamopoulosTechnological Educational Institute of Larissa

Department of Forestry an Management of Natural Environment431 00 Karditsa

GreeceE-mail: adamopoulos@teilar.gr

Tel. + 302441064706

Marina ChavenetidouAristotle University of Thessaloniki

School of Forestry and Natural EnvironmentLaboratory of Forest Utilization

541 24 ThessalonikiGreece

Costas PassialisAristotle University of Thessaloniki

School of Forestry and Natural EnvironmentLaboratory of Forest Utilization

541 24 ThessalonikiGreece

Elias VoulgaridisAristotle University of Thessaloniki

School of Forestry and Natural EnvironmentLaboratory of Forest Utilization

541 24 ThessalonikiGreece

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