Among-family variations of solid wood properties in 4-year-old Eucalyptus camaldulensis trees selected for pulpwood production in Thailand

Abstract

Solid wood properties were examined in eight half-sib families of 4-year-old Eucalyptus camaldulensis trees selected for pulpwood production in Thailand. The effects of radial growth rate on solid wood properties were also discussed. The mean values of green moisture content (MC) and basic density (BD) at 1.2 m heights in each family ranged from 86.3 to 106.6% and from 0.49 to 0.57 g cm⁻³, respectively. Significant among-family differences were found in MC, BD and maximum height of interlocked grain (IG). However, no significant correlations were found between stem diameter and solid wood properties, with the exception of MC and BD at a 5.2 m height, and IG. Based on the results obtained, it is suggested that superior E. camaldulensis trees, with respect to both growth characteristics and solid wood properties, can be selected for pulpwood production.

Keywords

Green moisture content Basic density Shrinkage Interlocked grain Radial growth rate Tree breeding

Introduction

Eucalyptus camaldulensis Dehnh. has been extensively planted in Asian countries for producing pulpwood. To increase the yield and quality of pulp, tree breeding programmes have been established for this species (Pinyopusarerk, Doran, Williams and Wasuwanich 1996; Sungtong and Diloksumpun 2011; Kuramochi et al. 2014). However, the demand for solid wood has been increasing in Asian countries owing to rapid economic growth, and pulpwood is not always dealt at a higher price when compared to solid wood; therefore, the possibility of solid wood production should be considered for fast-growing tree species, such as E. camaldulensis.

In the previous study (Ishiguri et al. 2013), we investigated the growth characteristics and solid wood properties, such as Young's modulus, of eight half-sib families of 4-year-old E. camaldulensis trees selected for pulpwood production in Thailand. We found significant family differences in the dynamic Young's modulus of the logs, and proposed that those trees with a high Young's modulus could be selected from those already selected for their growth characteristics in the previous tree breeding programmes (Ishiguri et al. 2013). However, other solid wood properties, such as basic density and shrinkage, have not yet been determined.

The relationships between growth characteristics and wood properties should be clarified in order to utilise the wood resources from fast-growing tree species. Many forest managers believe that fast-growing characteristics will lead to lower wood quality; however, no significant correlations have been found between radial growth rate and wood properties in fast-growing Eucalyptus spp. (Bamber, Horne and Graham-Higgs 1982; Wilkes 1984; Miranda, Almeida and Pereira 2001a, 2001b; Quilhó and Pereira 2001; Kojima et al. 2009a, 2009c; Ishiguri et al. 2013), as well as tropical fast-growing tree species, such as Falcataria moluccana, Acacia mangium and Gmelina arborea (Kojima et al. 2009b, 2009c; Makino et al. 2012; Ishiguri et al. 2016).

In the present study, to utilise the wood resources from fast-growing trees, solid wood properties, such as basic density, shrinkage and interlocked grain, were investigated for eight half-sib families of E. camaldulensis trees selected for pulpwood production. Based on the results, the effects of radial growth rate on the wood properties were also discussed.

Materials and methods

The progeny test site of E. camaldulensis was located in Wang Nam Khieo, Nakhon Ratchasima, Thailand (14°29′N, 101°56′E) (Sungtong and Diloksumpun 2011). This progeny test site was established in 2006 using seedlings of 120 half-sib families (open pollinated) selected as plus trees from Australia and Thailand based on the growth characteristics. Of 120 half-sib families, 10 showed superior growth and physiological characteristics (Sungtong and Diloksumpun 2011). In the present study, a total of 35 trees from eight families were selected from 10 families with superior growth and physiological characteristics (Table 1), because the number of trees in the progeny test site was limited for two families (Ishiguri et al. 2013). Four to five trees in each family were harvested (Ishiguri et al. 2013). As shown in Table 1, the mean stem diameter and tree height were 7.6 and 11.9 m, respectively. Two discs (3 and 5 cm in thickness) were collected at 1.2 and 5.2 m above the ground, respectively.

Table 1

Regions and provenance of the E. camaldulensis used in the second-generation progeny test, stem diameter at 1.3 m above ground and tree heights of the sample trees (Sungtong and Diloksumpun 2011; Ishiguri et al. 2013)

Region	Provenance	Family	n	Stem diameter (cm)		Tree height (m)
Region	Provenance	Family	n	Mean	SD	Mean	SD
Petford Region, QLD	Eureka creek	60	4	9.3^a	1.6	13.3^a	1.1
Petford Region, QLD	Petford bridge	71	4	7.7^ab	0.9	11.3^a	1.2
Walsh-Mitchell River, QLD	Walsh river rockwood	163	4	6.7^ab	1.0	11.2^a	1.2
Northern Territory, Western Australia and other QLD	Katherina	208	5	6.5^b	0.7	10.3^a	0.7
	Kennedy river	219	5	8.2^ab	1.1	13.0^a	1.1
	Morehead river	227	5	8.2^ab	1.2	12.5^a	1.7
Thailand	Thai selection	236	4	8.1^ab	1.4	12.0^a	2.1
Thailand	Thailand race (control)	996	4	6.6^ab	1.7	11.5^a	2.2
Mean/total			35	7.6	1.4	11.9	1.6

n, number of sample trees; SD, standard deviation. The same alphabet letters followed by the mean values indicate no significant differences at the 5% level based on the Tukey's HSD test.

For determining green moisture content and basic density, 2 cm-wide pith-to-bark strips were obtained from 3 cm-thick discs collected at 1.2 and 5.2 m above the ground level. Green moisture content and basic density were determined at 1 cm intervals from the pith to the bark. Green moisture content was determined by the oven-drying method, and basic density was calculated by dividing oven-dried weight by green volume, as measured by the water displacement method.

The specimens (20 (R) by 20 (T) by 10 (L) mm) were prepared from the 5 cm-thick discs collected at 1.2 m above the ground level to determine shrinkage, and three specimens were prepared from each tree. The dimensions in radial and tangential directions were determined using a micrometer screw gauge in green and oven-dried conditions. The mean value of a tree was calculated by averaging the data from these three specimens.

To evaluate interlocked grain, the discs (5 cm in thickness) obtained at 1.2 m above the ground were used. Baseline was drawn at long axis of transverse section. Then, the disc was split along the baseline with a wedge-shaped knife. After splitting, transverse section images were taken using a digital camera, and lengths of baseline and splitting line were determined by the image analysing software (ImageJ; National Institutes of Health). Interlocked grain was evaluated as a ratio of splitting line length to baseline length. In addition, the maximum height was defined as the maximum distance between base and splitting lines.

Results and discussion

Green moisture content and basic density

Table 2 shows the mean values of green moisture content and basic density at two different heights in each family. The lowest and highest green moisture contents at 1.2 m were observed in family 219 (86.3%) and family 71 (106.6%), respectively. A similar tendency was also found at 5.2 m height. The mean values of all of the trees were 98.1 and 99.0% for 1.2 and 5.2 m heights, respectively. On the other hand, the mean values of basic density ranged from 0.48 to 0.55 g cm⁻³ at 1.2 m height, and from 0.49 to 0.57 g cm⁻³ at 5.2 m height (Table 2). The mean value of all of the trees at 1.2 m height (0.50 g cm⁻³) was lower than that at 5.2 m height (0.53 g cm⁻³). Veenin, Fujita, Nobuchi and Siripatanadilok (2005) reported that the mean values of basic density in 5-year-old E. camaldulensis clones planted in Thailand ranged from 0.61 to 0.73 g cm⁻³. Moreover, Malan (1993) also reported that wood density varied from about 0.60 to 0.87 g cm⁻³ in 12-year-old eucalypt hybrids trees, reaching an average density of up to 0.96 g cm⁻³ when they became fully mature. Basic density in the outer wood (2 cm from the bark side) collected from 15 half-sib families of 5-year-old E. camaldulensis ranged from 0.51 to 0.61 g cm⁻³ (Kuramochi et al. 2014). Overall, our values obtained in basic density were lower than those obtained by previous researches (Veenin et al. 2005; Kuramochi et al. 2014).

Table 2

Among-family variations in the green moisture content and basic density at two different heights

Family	n	Green moisture content (%)				Basic density (g cm⁻³)
		1.2 m		5.2 m		1.2 m		5.2 m
		Mean	SD	Mean	SD	Mean	SD	Mean	SD
60	4	97.7^a	16.4	87.4^ab	8.9	0.52^ab	0.05	0.54^ab	0.04
71	4	106.6^a	10.1	104.2^a	5.2	0.48^ab	0.02	0.50^b	0.03
163	4	102.2^a	12.0	99.2^ab	15.1	0.48^b	0.03	0.49^b	0.04
208	5	98.0^a	14.2	94.9^ab	8.8	0.50^ab	0.03	0.51^ab	0.03
219	5	86.3^a	10.9	80.2^b	14.8	0.55^a	0.03	0.57^a	0.02
227	5	100.2^a	13.3	90.8^ab	5.5	0.51^ab	0.04	0.53^ab	0.03
236	4	103.9^a	13.1	90.0^ab	11.5	0.48^b	0.03	0.52^ab	0.02
996	4	99.9^a	14.5	81.7^ab	10.2	0.48^b	0.01	0.55^ab	0.03
Mean/total	35	98.1	13.4	99.0	12.5	0.50	0.04	0.53	0.04

n, number of sample trees; SD, standard deviation. The same alphabet letters followed by the mean value indicate no significant differences at the 5% level based on the Tukey's HSD test.

There were significant among-family differences in green moisture content at 5.2 m height and basic density at 1.2 and 5.2 m heights (Table 2). In one previous study, a significant among-family difference in basic density in most of outer wood was found in 10 families of E. camaldulensis (Kuramochi et al. 2014). In addition, Wang, Littell and Rockwood (1984) reported that differences in green moisture content and basic density among 20 progenies of E. grandis were significant, suggesting that selection is possible for increasing the density and lowering the green moisture content of E. grandis wood. Therefore, it is suggested that when the final wood products of E. camaldulensis are changed from pulpwood to solid lumber, the selection of superior trees with a lower green moisture content and higher wood density is possible from the trees (or families) selected for pulpwood production.

Figure 1 shows the relationships of green moisture content and basic density between two different heights. In both properties, the values at 1.2 m height were positively correlated with those at 5.2 m height. These results suggest that the whole tree values of green moisture content and basic density can be evaluated by the mean values obtained at 1.2 m height.

Miranda et al. (2001b) reported a significant correlation (r = 0.57) between basic densities of wood from 7-year-old and 9-year-old E. globulus trees. This result suggests that the early selection of trees with a high basic density is possible for E. globulus. In the present study, a significant positive correlation (r = 0.713) was found between basic densities at most inner and most outer parts (Fig. 2), suggesting that the selection of trees with a higher wood density is possible at a relatively early growth stage in E. camaldulensis, leading to a reduction in the breeding period for quality improvement of the wood in this species.

Shrinkage

Table 3 shows the mean values of shrinkage in radial and tangential directions for each family, which ranged from 4.9% (family 236) to 6.9% (family 219), and from 9.1% (family 208) to 12.6% (family 71), respectively. The mean values of all of the trees were 5.8 and 11.0% in the radial and tangential directions, respectively. Malan (1993) reported that radial and tangential shrinkages were 4.7 and 9.7% for E. grandis × E. camaldulensis, 5.5 and 10.3% for E. grandis × E. tereticornis, 5.0 and 9.4% for E. grandis × E. urophylla, and 4.0 and 7.5% for E. grandis, respectively. In 11-year-old three Eucalyptus species, radial and tangential shrinkage values of middle wood (collected from a 50% relative radial distance from pith) were 6.8 and 10.3% for E. urophylla, 5.6 and 8.9% for E. grandis, and 5.6 and 9.2% for E. urophylla × E. grandis, respectively (Wu et al. 2006). Shrinkage values in the radial and tangential directions in 4-year-old E. camaldulensis used in the present study were in the range of other Eucalyptus trees. In approximately 400 open-pollinated families of E. nitens, Hamilton, Raymond, Harwood and Potts (2009) reported that significant genetic variation at the race and/or within-race level was identified in gross shrinkage. In the present study, however, no significant among-family differences were found in either direction (Table 3).

Table 3

Among-family variations in the radial and tangential shrinkage

Family	n	Radial direction (%)		Tangential direction (%)
Family	n	Mean	SD	Mean	SD
60	4	5.2^a	1.5	10.6^a	2.1
71	4	6.3^a	0.7	12.6^a	2.0
163	4	6.0^a	1.4	10.8^a	1.1
208	5	5.4^a	1.0	9.1^a	0.9
219	5	6.9^a	1.5	12.3^a	2.4
227	5	5.8^a	1.1	11.5^a	2.1
236	4	4.9^a	0.9	10.5^a	2.5
996	4	5.7^a	2.4	10.2^a	2.0
Mean/total	35	5.8	1.4	11.0^a	2.1

n, number of sample trees; SD, standard deviation. The same alphabet letters followed by the mean values indicate no significant differences at the 5% level based on the Tukey's HSD test.

Interlocked grain

The ratio of splitting line to baseline ranged from 8.1% (family 163) to 30.6% (family 60) (Table 4). A similar trend was found in the maximum height: the largest and smallest values were observed in family 60 (11.4 mm) and family 163 (2.7 mm), respectively. In softwoods, it has been reported that the heritability (or repeatability) of spiral grain showed relatively high values in Larix kaempferi (Mikami, Watanabe and Ohta 1972) and Picea abies (Cost e Silva, Borralho and Wellendorf 2000). In addition to softwoods, the spiral grain is also heritable in Eucalyptus dunnii (Thinley, Palmer, Vanclay and Henson 2005). In the present study, due to the large standard deviation values within the families, no significant among-family difference was found in the ratio of splitting line to baseline. However, the maximum height showed a significant among-family difference. Therefore, it is suggested that E. camaldulensis trees with lower interlocked grain wood may be selected by tree breeding.

Table 4

Among-family variations in the interlocked grain

Family	n	Splitting / base (%)		Maximum height (mm)
Family	n	Mean	SD	Mean	SD
60	4	30.6^a	20.9	11.4^a	5.0
71	4	16.1^a	9.6	8.5^ab	2.9
163	4	8.1^a	3.4	2.7^b	1.6
208	5	28.1^a	6.9	5.2^b	1.8
219	5	11.9^a	6.9	5.0^b	2.1
227	5	12.5^a	7.7	4.1^b	1.8
236	4	13.0^a	9.0	4.8^b	2.4
996	4	11.2^a	8.1	4.4^b	2.5
Mean/total	35	16.5	11.9	5.7	3.5

n, number of sample trees; SD, standard deviation. The same alphabet letters followed by the mean values indicate no significant differences at the 5% level based on the Tukey's HSD test.

Effects of the radial growth rate on wood properties

Zobel and van Buijtenen (1989) mentioned that fast growth in ring-porous hardwoods results in dense wood, while in diffuse-porous woods, the growth rate differences have little effect on the wood density. In Eucalyptus spp., many researchers have investigated the effects of growth rate on anatomical characteristics and wood properties (Bamber et al. 1982; Wilkes 1984; Ohbayashi and Shiokura 1990; Miranda et al. 2001a, 2001b; Quilhó and Pereira 2001; Kojima et al. 2009a, 2009c; Ishiguri et al. 2013). Bamber et al. (1982) reported that, in 2.5-year-old E. grandis, wood of fast-growth trees was similar to that of slower-growth trees with respect to basic density and fibre dimensions, whereas vessels were smaller and less numerous, and ray volume was greater in fast-growth trees. In addition, Miranda et al. (2001a) reported that no correlation could be found between basic density and stem diameter or the tree height in 7-year-old E. globulus.

In E. grandis, Kojima et al. (2009a) found that the lateral growth rate did not significantly affect longitudinally released strain of surface growth stresses or the wood density of the samples collected from tropical to subtropical Brazil and subtropical Argentina. Other studies have had similar results, finding no correlations between growth rate and anatomical characteristics and the wood properties in six 40-year-old Eucalyptus spp. (Wilkes 1984), 26-year-old E. alba (Wahyudi et al. 2015) and 15-year-old E. globulus (Quilhó and Pereira 2001). On the other hand, Ohbayashi and Shiokura (1990) reported that oven-dried density was higher in small-diameter stems than in large-diameter ones in 4-year-old E. saligna grown in the Philippines. In our previous study (Ishiguri et al. 2013), we found no correlation between stem diameter and dynamic Young's modulus of the logs.

Table 5 shows the correlation coefficients between stem diameter and wood properties in this study. No significant correlation coefficients were recognised between stem diameter and wood properties, with the exception of green moisture content and basic density at the 5.2 m height, and the maximum height of interlocked grain, suggesting that faster-growth characteristics in E. camaldulensis do not always produce solid wood with a lower quality. Therefore, it is suggested that superior E. camaldulensis trees, with respect to both growth characteristics and solid wood properties, can be obtained from those already selected for pulpwood production.

Table 5

Correlation coefficients between the stem diameter and wood properties in the sample trees

Wood property	Correlation coefficient
Moisture content at 1.2 m	−0.292 ns
Moisture content at 5.2 m	−0.354*
Basic density at 1.2 m	0.302 ns
Basic density at 5.2 m	0.348*
Shrinkage in radial direction	−0.083 ns
Shrinkage in tangential direction	0.176 ns
Ratio of splitting line to base line	0.216 ns
Maximum height of interlocked grain	0.422*

*Significant at the 5% level; ns, no significance.

Conclusion

In this research, the solid wood properties were investigated for eight half-sib families of 4-year-old Eucalyptus camaldulensis trees planted in Thailand. Based on the results obtained, the effects of radial growth rate on solid wood properties were also discussed. Among eight families, the largest mean stem diameter (9.3 cm) and mean tree height (13.3 m) were found in family 60. The mean values of green moisture content in all of the trees were 98.1 and 99.0% for 1.2 and 5.2 m heights, respectively, while basic density values at 1.2 and 5.2 m heights were 0.50 and 0.53 g cm⁻³, respectively. Significant correlations in green moisture content and basic density were found between 1.2 and 5.2 m heights. In addition, there was a significant correlation between mean values of the basic density at pith and outer parts, suggesting that the early selection of superior trees with a higher basic density is possible for this species. The mean values of shrinkage in radial and tangential directions for each family were 5.8 and 11.0%, respectively, and the ratio of splitting line to baseline ranged from 8.1 to 30.6%. Moreover, the largest and smallest values in the maximum height of interlocked grain were 11.4 and 2.7 mm, respectively. Significant among-family variations were found in green moisture content at 5.2 m height, basic density at 1.2 and 5.2 m heights, and the maximum distance of interlocked grain. There were no significant correlations between stem diameter and solid wood properties tested here, with the exception of green moisture content and basic density at 5.2 m height, and the maximum height of interlocked grain. Based on the results of this study, it is suggested that E. camaldulensis trees with superior growth characteristics and solid wood properties can be selected from those already selected for pulpwood production.

References

Bamber

R. K.

, Horne

and Graham-Higgs

1982. Effect of fast growth on the wood properties of Eucalyptus grandis. Australian Forestry Research. 12: 163–167.

Costa e Silva

, Borralho

N. M. G.

and Wellendorf

2000. Genetic parameter estimates for diameter growth, Pilodyn penetration and spiral grain in Picea abies (L.) Karst. Silvae Genetica. 49: 29–36.

Hamilton

M. G.

, Raymond

C. A.

, Harwood

C. E.

and Potts

B. M.

2009. Genetic variation in Eucalyptus nitens pulpwood and wood shrinkage traits. Tree Genetics and Genomes. 5: 307–316. doi: 10.1007/s11295-008-0179-4

Ishiguri

, Aiso

, Hirano

, Yahya

, Wahyudi

, Ohshima

, Iizuka

and Yokota

2016. Effects of radial growth rate on anatomical characteristics and wood properties of 10-year-old Dysoxylum mollissimum trees planted in Bengkulu, Indonesia. Tropics. 25: 23–31. doi: 10.3759/tropics.25.23

Ishiguri

, Diloksumpun

, Tanabe

, Iizuka

and Yokota

2013. Stress-wave velocity of trees and dynamic Young's modulus of logs of 4-year-old Eucalyptus camaldulensis trees selected for pulpwood production in Thailand. Journal of Wood Science. 59: 506–511. doi: 10.1007/s10086-013-1363-1

Kojima

, Yamaji

F. M.

, Yamamoto

, Yoshida

and Nakai

2009a. Effects of the lateral growth rate on wood quality parameters of Eucalyptus grandis from different latitudes in Brazil and Argentina. Forest Ecology and Management. 257: 2175–2181. doi: 10.1016/j.foreco.2009.02.026

Kojima

, Yamamoto

, Marsoem

S. N.

, Okuyama

, Yoshida

, Nakai

, Yamashita

, Saegusa

, Matsune

, Nakamura

, Inoue

and Arizono

2009b. Effects of the lateral growth rate on wood quality of Gmelina arborea from 3.5-, 7- and 12-year-old plantations. Annals of Forest Science. 66: 507. doi: 10.1051/forest/2009031

Kojima

, Yamamoto

, Okumura

, Ojio

, Yoshida

, Okuyama

, Ona

, Matsune

, Nakamura

, Ide

, Marsoem

S. N.

, Sahri

M. H.

and Hadi

Y. S.

2009c. Effect of the lateral growth rate on wood properties in fast-growing hardwood. Journal of Wood Science. 55: 417–424. doi: 10.1007/s10086-009-1057-x

Kuramochi

, Aiso

, Diloksumpun

, Tanabe

, Ohshima

, Ishiguri

, Takashima

, Iizuka

, Yokota

, Aizawa

and Ohkubo

2014. Among-family variation of wood properties relating to pulp qualities in 5-year-old Eucalyptus camaldulensis planted in the northeastern region of Thailand (In Japanese). Forest Genetics and Tree Breeding. 3: 146–152.

10.

Makino

, Ishiguri

, Wahyudi

, Takashima

, Iizuka

, Yokota

and Yoshizawa

2012. Wood properties of young Acacia mangium trees planted in Indonesia. Forest Products Journal. 62: 102–106. doi: 10.13073/0015-7473-62.2.102

11.

Malan

F. S.

1993. The wood properties and qualities of three South African-grown eucalypt hybrids. South African Forestry Journal. 167: 35–44. doi: 10.1080/00382167.1993.9629409

12.

Mikami

, Watanabe

and Ohta

1972. Clonal variation in spiral grain of Larix leptolepis Gord. (in Japanese). Journal of Japan Forestry Society. 54: 213–217.

13.

Miranda

, Almeida

M. H.

and Pereira

2001a. Influence of provenance, subspecies, and site on wood density in Eucalyptus globulus Labill. Wood and Fiber Science. 33: 9–15.

14.

Miranda

, Almeida

M. H.

and Pereira

2001b. Provenance and site variation of wood density in Eucalyptus globulus Labill. at harvest age and its relation to a non-destructive early assessment. Forest Ecology and Management. 149: 235–240. doi: 10.1016/S0378-1127(00)00560-0

15.

Ohbayashi

and Shiokura

1990. Wood anatomical characteristics and specific gravity of fast-growing tropical tree species in relation to growth rate. Mokuzai Gakkaishi. 36: 889–893.

16.

Pinyopusarerk

, Doran

J. C.

, Williams

E. R.

and Wasuwanich

1996. Variation in growth of Eucalyptus camaldulensis provenances in Thailand. Forest Ecology and Management. 87: 63–73. doi: 10.1016/S0378-1127(96)03835-2

17.

Quilhó

and Pereira

2001. Within and between-tree variation of bark content and wood density of Eucalyptus globulus in commercial plantations. IAWA Journal. 22: 255–265. doi: 10.1163/22941932-90000283

18.

Sungtong

and Diloksumpun

2011. Variations in physiological characteristics of different Eucalyptus camaldulensis Dehnh. half-sib families. Thai Journal of Forstry. 30(3): 1–13.

19.

Thinley

, Palmer

, Vanclay

J. K.

and Henson

2005. Spiral and interlocking grain in Eucalyptus dunnii. Holz als Roh- und Werkstoff. 63: 372–379. doi: 10.1007/s00107-005-0011-x

20.

Veenin

, Fujita

, Nobuchi

and Siripatanadilok

2005. Radial variations of anatomical characteristics and specific gravity in Eucalyptus camaldulensis clones. IAWA Journal. 26: 353–361. doi: 10.1163/22941932-90000120

21.

Wahyudi

, Ishiguri

, Makino

, Tanabe

, Tan

, Tuhumury

, Iizuka

and Yokota

2015. Growth characteristics and wood properties of 26-year-old Eucalyptus alba planted in Indonesia. International Wood Products Journal. 6: 84–88. doi: 10.1179/2042645315Y.0000000003

22.

Wang

, Littell

R. C.

and Rockwood

D. L.

1984. Variation in density and moisture content of wood and bark among twenty Eucalyptus grandis progenies. Wood Science and Technology. 18: 97–100. doi: 10.1021/es00121a718

23.

Wilkes

1984. The influence of rate of growth on the density and heartwood extractives content of eucalypt species. Wood Science and Technology. 18: 113–120. doi: 10.1021/es00120a013

24.

Y. Q.

, Hayashi

, Liu

, Cai

and Sugimori

2006. Relationships of anatomical characteristics versus shrinkage and collapse properties in plantation-grown eucalypt wood from China. Journal of Wood Science. 52: 187–194. doi: 10.1007/s10086-005-0751-6

25.

Zobel

B. J.

and van Buijtenen

J. P.

1989. Wood variation, its causes and control. Berlin: Springer-Verlag.