Variations on growth characteristics and wood properties of three Eucalyptus species planted for pulpwood in Indonesia

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1 ISSN : X DOI: /tropics.MS16-15 TROPICS Vol. 26 (2) Issued September 1, 2017 ORIGINAL ARTICLE Variations on growth characteristics and wood properties of three Eucalyptus species planted for pulpwood in Indonesia Agung Prasetyo 1, 2, Haruna Aiso 1, 2, Futoshi Ishiguri 1*, Imam Wahyudi 3, I Putu G. Wijaya 4, Jyunichi Ohshima 1 and Shinso Yokota 1 1 Faculty of Agriculture, Utsunomiya University, Utsunomiya , Japan 2 United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo , Japan 3 Faculty of Forestry, Bogor Agricultural University, Bogor 16680, Indonesia 4 Toba Pulp Lestari, Tbk., Medan 20231, Indonesia * Corresponding author: ishiguri@cc.utsunomiya-u.ac.jp Received: January 18, 2017 Accepted: May 9, 2017 ABSTRACT Fast-growing tree species are being considered as an alternative source of timber to augment the supply in southern Asian countries. Eucalyptus is one of the most promising genus because its fast-growing characteristics and hybridization among species can produce superior characteristics valuable to both the pulp and timber industries. To evaluate the possibility of using it for timber, growth characteristics and wood properties were investigated for three nine-year-old Eucalyptus species (E. urophylla, E. grandis, and E. pellita) planted for pulpwood in Indonesia. E. pellita showed superior growth characteristics and wood properties compared to the other two species. No negative correlation coefficients were observed between growth characteristics and wood properties in any of the species, indicating that improvement of wood properties might not reduce the growth characteristics. The hybrids from E. pellita and E. urophylla might produce a next generation with better growth characteristics, resistance to pests and diseases, tolerance to low soil fertility, and relatively good wood properties. In addition, based on the obtained results, hybridization between E. grandis and E. urophylla or E. pellita might improve the relatively low wood properties of E. grandis. Key words: E. urophylla, E. grandis, E. pellita, physical and mechanical properties, microfibril angle INTRODUCTION The genus Eucalyptus is one of the most promising trees for forestry, and the wood and pulp industries (Wu et al. 2006, Clarke et al. 2009, Ishiguri et al. 2013, Hung et al. 2015, Wessels et al. 2016). In many countries, fast-growing Eucalyptus species have been mainly cultivated for producing pulpwood (Wei and Borralho 1999, Raymond 2002, Hung et al. 2015). On the other hand, in tropical regions, timber wood is mostly produced from the slowgrowing tree species in natural forests such as Shorea species and the teak (Tectona grandis) (Bosman et al. 1994, Miranda et al. 2011). The limited timber production from natural forests leads to a lack of sufficient timber supply, a situation which is being exacerbated by excessive deforestation. Therefore, the fast-growing plantation tree species, such as Eucalyptus spp., are expected to meet the large demand for wood instead of wood from natural forests. Hybridization among the Eucalyptus species is important for developing superior trees with better growth characteristics, adaptability to the environment and climate, resistance to pests and diseases, and valuable wood properties (Malan 1993, Gwaze et al. 2000, Quilho et al. 2006, Grattapaglia and Kirst 2008, Listyanto et al. 2010, Nichols et al. 2010). E. urophylla, E. grandis, and E. pellita have been used for producing interspecific hybrids showing the superior growth characteristics and wood properties required for the pulp and paper industries (Wei and Borralho 1999, Quilho et al. 2006, Wu et al. 2011, Sharma et al. 2015). Among these species, E. urophylla and E. pellita have dense wood, and the wood properties of the two species can be improved for use as timber by an appropriate breeding strategy (Soerianegara and Lemmens 1994, Hung et al. 2015). In addition, E. grandis is well known for its fast-growing characteristics and adaptability to a wide range of environmental conditions (Clarke et al. 2009, Listyanto et al. 2010, Nichols et al. 2010). Research on wood properties and their relationships with growth characteristics is therefore important when considering the Eucalyptus species for timber production. Furthermore, the

2 60 TROPICS Vol. 26 (2) Agung Prasetyo, Haruna Aiso et al. obtained information can also be used when designing appropriate tree breeding programs and producing the hybrids among these species. In the present study, growth characteristics (stem diameter and tree height), stress-wave velocity of the stem, and wood properties (basic density, shrinkage, compressive strength, modulus of elasticity, modulus of rupture, and microfibril angle) were investigated for three nine-year-old Eucalyptus species (E. urophylla, E. grandis, and E. pellita) planted in North Sumatra, Indonesia. In addition, the practical implications for hybridization among these species were also discussed. Experimental stand MATERIALS AND METHODS In the present study, nine-year-old trees of three Eucalyptus species (E. urophylla S. T. Blake, E. grandis W. Hill ex Maiden, and E. pellita F. Muell.) were used. These trees were planted for pulpwood production in North Sumatra, Indonesia (2 46 N and E, 1250 m in altitude). The seeds of E. urophylla, E. grandis, and E. pellita originated from East Timor, Australia, and Papua New Guinea, respectively. At the site, the trees were planted in m spacing. No thinning and pruning were applied, while fertilizer (N, TSP, and rock phosphate) was applied when the trees were planted. Growth characteristics and stress-wave velocity of the stem Stem diameter (D) at 1.3 m above the ground, tree height (TH), and stress-wave velocity (SWV) were measured for E. urophylla (19 trees), E. grandis (8 trees), and E. pellita (11 trees). D and TH were measured by diameter tape and ultrasound height meter (Vertex IV, Haglöf), respectively. SWV was measured by a stress-wave timer (Fakopp microsecond timer, Fakopp Enterprise) as described by previous paper (Ishiguri et al. 2016). The start and stop sensors were set on the surface of the stem from 0.5 to 1.5 m above the ground. The stress-wave propagation time was measured six times at the same position on the stem by hitting the start sensor with a small hammer. The SWV was determined by dividing the distance between two sensors by the mean value of the stress-wave propagation time. Wood properties After measuring the standing tree characteristics, three trees with the mean diameter in each species were felled to obtain the samples for laboratory experiments such as basic density (BD), microfibril angle (MFA), shrinkage properties, modulus of elasticity (MOE), modulus of rupture (MOR), and compressive strength parallel to grain (CS). Discs (30 mm thick) and small logs (10 cm long) were collected from 1.3 m above the ground, and these samples were used for measuring BD and MFA, and for measuring shrinkage and mechanical properties, respectively. For measuring BD and MFA, the 30 mm discs were cut into 10 mm thick samples. Small blocks were collected from each disc at 1 cm interval from pith to bark. The BD was calculated as the ratio of oven-dry weight to green volume, determined through the water displacement method (Barnett and Jeronimidis 2003). The MFA of the S 2 layer in wood fibers was measured with the iodine method (Senft and Bendtsen 1985). A sliding microtome (REM-710, Yamato Koki) was used to prepare radial sections (20 µm in thickness) from the small blocks collected from each 1 cm interval from pith to bark side. These sections were soaked in Schulzeʼs solution (100 ml of 35 % nitric acid, 6 g potassium chlorate) for 20 minutes, and then dehydrated with a graded ethanol. The dehydrated sections were successively treated with a drop of iodine-potassium iodide solution and a drop of 60 % nitric acid. Photomicrographs were captured by a digital camera (E-330, Olympus) attached to a light microscope (CX-41, Olympus). MFA was determined for 30 fibers in each radial position by using image analysis software (ImageJ, National Institute of Health). Samples (10 (L) 10 (R) 10 (T) mm) from pith to bark side for measuring the shrinkage were prepared from the boards that were cut from the 10 cm long logs. The dimensional changes under the air-dry and oven-dry (105 ) conditions were measured with a screw micrometer (M310 25, Mitutoyo). The radial shrinkage (RS) and tangential shrinkage (TS) per 1 percent change in moisture content (MC) were calculated by the formula described in the previous paper (Istikowati et al. 2014). The T/R shrinkage ratio was also calculated after calculating the radial and tangential shrinkage per 1 percent change in MC. Small-clear specimens (65 (L) 10 (R) 4 (T) mm) from pith to bark side were prepared for a static bending test. A total of 230 small-clear specimens were used to determine the MOE and MOR. A universal testing machine (MSC-5/500 2, Tokyo Testing Machine) with 45 mm span and 0.5 mm min 1 load speed was used. The mean

3 Growth characteristics and wood properties of Eucalyptus planted in Indonesia 61 Table 1. Statistical values of growth characteristics and SWV in three Eucalyptus species. Property Species n Min. Max. Mean SD E. urophylla b 3.1 D (cm) E. grandis ab 1.9 E. pellita a 3.2 E. urophylla b 3.0 TH (m) E. grandis a 5.1 E. pellita a 3.2 E. urophylla a 0.29 SWV (km s 1 ) E. grandis a 0.23 E. pellita a 0.30 Note: n, Number of trees; Min., minimum; Max., maximum; SD, standard deviation; D, stem diameter; TH, tree height; SWV, stress-wave velocity. Different letters after mean value indicates significant difference among the three Eucalyptus species (Tukey-HSD, 5 %). standard deviation of the specimensʼ moisture content was %. After data were obtained from the test, the MOE and MOR were calculated by the equations described by Kollmann and Côté (1984). CS was determined using small-clear specimens (40 (L) 10 (R) 10 (T) mm) from pith to bark side. A total of 132 small-clear specimens were tested. The mean standard deviation of these specimensʼ moisture content was %. A universal testing machine (RTF-2350, A&D) was used for determining the maximum load of each specimen at 0.5 mm min 1 load speed. CS was determined by dividing the maximum load by the transverse sectional area of the specimen (Kollmann and Côté 1984). Data analysis Multiple comparison (Tukey-HSD) test was performed to analyze the significant difference on the data from growth characteristics, SWV, and wood properties of the three Eucalyptus species. The relationships between the measured properties were determined using Pearsonʼs correlation analysis. Multiple regression analysis was also performed to generate the equation models describing the interactions. All statistical analyses were carried out at a 5 % level using the R open-source statistical package (R Core Team 2013). RESULTS AND DISCUSSION Growth characteristics and wood properties The mean values for stem diameter (D) in E. urophylla, E. grandis, and E. pellita were 13.1, 14.0, and 16.8 cm, respectively (Table 1). Based on the Tukey HSD test (5 % level), the values for E. pellita were significantly higher than that of E. urophylla. The tree height (TH) of E. pellita (16.7 m) and E. grandis (17.1 m) were significantly higher compared to that of E. urophylla (12.1 m). Several researchers have found that E. pellita has promising growth characteristics (D and TH) compared to E. urophylla and other Eucalyptus species in Indonesia (Harwood et al. 1997, Leksono et al. 2008). Our results were similar to those reported by the previous researchers. The stress-wave velocity (SWV) in the three Eucalyptus species ranged from 2.64 to 3.89 km s 1 (Table 1). No significant difference in SWV was observed among the three Eucalyptus species. The SWV ranged from 2.76 to 4.35 km s 1 in four-year-old E. camaldulensis (Ishiguri et al. 2013), from 3.18 to 3.36 km s 1 in 13-year-old E. nitens (Blackburn et al. 2010), and from 3.08 to 3.30 km s 1 in 26-year-old E. alba (Wahyudi et al. 2015). The SWV values obtained in this studyʼs three nine-year-old Eucalyptus species were in the range of those reported in other Eucalyptus species. Basic density (BD) ranged from 0.32 to 0.66 g cm 3 in three Eucalyptus species (Table 2). The mean values for BD were 0.46 g cm 3 (E. urophylla), 0.41 g cm 3 (E. grandis), and 0.46 g cm 3 (E. pellita) (Table 2). Although two species,

4 62 TROPICS Vol. 26 (2) Agung Prasetyo, Haruna Aiso et al. Table 2. Statistical values of wood properties in three Eucalyptus species. Property Species n Min. Max. Mean SD E. urophylla a 0.10 BD (g cm -3 ) E. grandis a 0.05 E. pellita a 0.06 E. urophylla a 3.0 MFA ( o ) E. grandis a 2.3 E. pellita a 4.3 E. urophylla b 0.06 RS (%) E. grandis ab 0.04 E. pellita a 0.04 E. urophylla b 0.04 TS (%) E. grandis a 0.04 E. pellita a 0.03 E. urophylla a 0.4 T/R E. grandis a 0.4 E. pellita b 0.4 E. urophylla a 11.6 CS (MPa) E. grandis b 8.6 E. pellita ab 6.9 E. urophylla a 1.89 MOE (GPa) E. grandis b 1.08 E. pellita ab 1.64 E. urophylla a 26.4 MOR (MPa) E. grandis b 15.9 E. pellita ab 23.4 Note: n, Number of samples; Min., minimum; Max., maximum; SD, standard deviation; BD, basic density; MFA, microfibril angle; RS and TS, radial and tangential shrinkages at 1 % change in moisture content, respectively; T/R, tangential shrinkage to radial shrinkage ratio; CS, compressive strength parallel to grain; MOE, modulus of elasticity; MOR, modulus of rupture. Different letters after mean value indicates significant difference among the three Eucalyptus species (Tukey-HSD, 5 %). E. urophylla and E. pellita, showed higher mean values than E. grandis, no significant differences were found among species. BD was almost constant up to 3 cm from the pith, and then it gradually increased toward the bark (Fig. 1). In 11-year-old E. urophylla, the BD values were 0.42 g cm 3 for 10 % (around pith), 0.48 g cm 3 for 50 % (middle position), and 0.52 g cm 3 for 90 % (near bark) from pith to bark (Wu et al. 2006). Bhat et al. (1990) also reported that the mean BD value varied from 0.42 to 0.62 g cm 3 in nine-year-old E. grandis grown in India. They also explained that the BD in E. grandis decreased initially from pith to bark and then it gradually increased towards the bark. FWPA (2008) reported that the mean value of BD in 15-year-old E. pellita ranged from 0.45 to 0.65 g cm 3, and the values increased radially from the inner to the outer heartwood. Our results on the radial variation of BD were similar to those reported in these species by previous researchers. The mean values of the microfibril angle (MFA) were 9.2 (E. urophylla), 10.0 (E. grandis), and 11.0 (E. pellita) (Table 2). The MFA values decreased from around 15 to 5 toward the bark side in three Eucalyptus species (Fig. 2). Some researchers have reported the values of MFA as measured by X-ray diffraction and NIR spectroscopy (Hein et al. 2013, Hung et al. 2015). In one of those studies, the mean MFA for a six-year-old hybrid (E. urophylla and E. grandis) was 12.1 (Hein et al. 2013). Hung et al. (2015) reported that the mean MFA values in nine 10-year-old clones of E. pellita were 15.1 and 14.5 in Pleiku and Bau Bang, Vietnam, respectively. Decreasing values of MFA

5 Growth characteristics and wood properties of Eucalyptus planted in Indonesia 63 Fig. 1. Radial variations of basic density (BD) Note: n, Number of samples; solid lines indicate mean values. Fig. 2. Radial variations of microfibril angle (MFA) of S 2 layer in wood fibers Note: n, Number of samples; solid lines indicate mean values. Fig. 3. Radial variations of radial (RS) and tangential (TS) shrinkages per 1 percent change in moisture content Note: n, Number of samples; solid lines indicate mean values.

6 64 TROPICS Vol. 26 (2) Agung Prasetyo, Haruna Aiso et al. from pith to bark in Eucalyptus species have also been found by a number of other researchers (Medhurst et al. 2012, Hein et al. 2013, Wessels et al. 2016). However, due to difference of the measurement methods, the MFA in the present study showed relatively lower values compared to those obtained by other researchers. The radial shrinkage (RS) and tangential shrinkage (TS) per 1 percent change in moisture content (MC) of the three Eucalyptus species ranged from 0.07 to 0.29 % and from 0.19 to 0.39 %, respectively (Table 2). The highest mean values of RS (0.22 %) and TS (0.31 %) were found in E. urophylla. On the other hand, the T/R ratio in E. pellita (1.8) was higher than that of the other two Eucalyptus species (i.e. T/R 1.5 for both of them). The total shrinkage in radial and tangential directions from green to oven-dry conditions and the T/R ratio were 4.8 %, 7.8 %, and 1.7 in six-year-old E. urophylla E. grandis, respectively (Hein et al. 2013). In the present study, smaller values of the T/R ratio were found in E. urophylla and E. grandis, indicating less surface checking and lumber deformation in these two species during drying compared to the E. pellita wood. The radial variations from pith to bark in RS and TS are shown in Fig. 3. In the three Eucalyptus species, RS values decreased from pith outwards to 2 cm, and then remained constant or increased toward the bark. Radial variation in TS gradually increased from pith to bark for the three Eucalyptus species. Wu et al. (2006) reported that the RS and TS increased from the inner wood to the middle wood and then slightly increased or remained constant toward the bark in 11-year-old E. urophylla and E. grandis from China. In E. pellita, the shrinkage properties also increased from pith to bark (FWPA 2008). Therefore, the results in the present study showed a general pattern of the shrinkage properties in Eucalyptus species. The compressive strength parallel to grain (CS), modulus of elasticity (MOE), and modulus of rupture (MOR) were 12.7 to 58.5 MPa, 3.07 to GPa, and 40.5 to MPa in three Eucalyptus species, respectively (Table 2). The radial variations in these three mechanical properties gradually increased from pith to bark except for E. urophylla: the values decreased up to 2 cm and then increased toward the bark for CS, and showed decreasing values near the bark for MOE and MOR (Figs. 4 and 5). The CS, MOE, and MOR estimated by NIR spectroscopy were 40.1 to 63.6 MPa, 11.1 to 20.2 GPa, and 69.9 to MPa in seven-year-old E. urophylla grown in Brazil (Andrade et al. 2010). Cademartori et al. (2014) reported that the MOE of seven-year-old E. grandis obtained through a static bending test was 11.2 to 13.0 GPa from the heartwood to the sapwood. In 15-year-old E. pellita, the Fig. 4. Radial variations of compressive strength parallel to grain (CS) Note: n, Number of samples; solid lines indicate mean values. mean values of CS, MOE, and MOR were 76.0 MPa, 13.6 GPa, and 108 MPa, respectively, and these properties tended to increase from the inner to the outer heartwood (FWPA 2008). Based on the results, E. urophylla was found to show higher mechanical strength (MOE, MOR, and CS) compared to the E. grandis (Table 2). Relationships among measured properties Relationships between growth characteristics and SWV are shown in Fig. 6. Highly positive, significant correlation coefficients were obtained between D and TH, except for E. pellita. Positive correlation coefficients were also obtained between growth characteristics and SWV, except for E. pellita. In other Eucalyptus species (E. dunnii, E. camaldulensis, and E. alba), significant correlation coefficients were obtained between D and SWV (Dickson et al. 2003, Ishiguri et al. 2013, Wahyudi et al. 2015). It is well known that SWV is positively correlated with dynamic Youngʼs modulus of logs (Dickson et al. 2003, Ishiguri et al. 2013). Based on this studyʼs results, it is considered that improvement on the growth characteristics in three Eucalyptus species does not lead to a reduction in Youngʼs

7 Growth characteristics and wood properties of Eucalyptus planted in Indonesia 65 Fig. 5. Radial variations of modulus of elasticity (MOE) and modulus of rupture (MOR) in static bending Note: n, Number of samples; solid lines indicate mean values. Fig. 6. Relationships between growth characteristics and stress-wave velocity in three Eucalyptus species Note: n, number of trees; D, stem diameter; TH, tree height; r, correlation coefficient; ns, no significance; *P 0.05, **P 0.01 (Pearsonʼs analysis).

8 66 TROPICS Vol. 26 (2) Agung Prasetyo, Haruna Aiso et al. modulus of wood, suggesting that selection of trees with superior growth characteristics will result the production of solid lumber with higher strength properties. In addition, SWV can be used as a rapid and non-destructive technique to predict the mechanical properties of Eucalyptus wood. Wu et al. (2006) found BD to be an unsatisfactory indicator of shrinkage properties, in particular for low to medium BD in E. urophylla and E. grandis. Hein et al. (2013) found that BD was unable to predict the total shrinkage properties (r 0.39 for total radial shrinkage, r 0.43 for total tangential shrinkage) in a six-year-old hybrid of E. urophylla E. grandis. In the present study, no significant correlation coefficients between BD and RS or TS were obtained in three Eucalyptus species, except for BD and RS in E. urophylla (Table 3), suggesting that BD is unsuitable as a predictor for wood shrinkage in Eucalyptus species. BD had highly positive, significant correlations with the three mechanical properties tested in the present study (Table 3). Similarly, MFA had also strong relationships with the three measured mechanical properties in the three species, except for CS in E. grandis (Table 3). Wessels et al. (2016) found that both BD and MFA have significant Table 3. Relationships between the wood properties in three Eucalyptus species. Species Property BD MFA BD + MFA a MFA 0.29 RS 0.53* * E. urophylla TS * CS 0.82** ** MOE 0.82** ** MOR 0.88** ** MFA 0.44 RS E. grandis TS CS 0.51* * MOE 0.62* 0.66** 0.76** MOR 0.56* 0.52* 0.64** MFA 0.89** RS E. pellita TS CS 0.82** 0.81** 0.84** MOE 0.90** 0.85** 0.91** MOR 0.90** 0.86** 0.91** Note: BD, basic density; MFA, microfibril angle; RS and TS, radial and tangential shrinkages per 1 % change in moisture content, respectively; CS, compressive strength parallel to grain; MOE, modulus of elasticity; MOR, modulus of rupture; *P 0.05, **P 0.01; a result from multiple regression analysis. correlations with MOE and MOR in 20-year-old Eucalyptus species grown in Southern Africa. This result suggests that the three mechanical properties of wood in the Eucalyptus species cannot only be explained by BD. In the present study, therefore, the combined effects of BD and MFA on the mechanical properties were evaluated. Correlation coefficients between the mechanical properties and BD+MFA were higher than those between mechanical properties and BD or MFA. Hein et al. (2013) reported that BD and MFA highly influenced the MOE (r 0.81) in sixyear-old E. grandis E. urophylla. Similarly, Wessels et al. (2016) found that three independent variables, such as BD, MFA, and grain angle, highly influence the MOE (r 0.81) in Eucalyptus species planted in South Africa. Based on the results obtained, it is considered that the mechanical properties of wood in three Eucalyptus species are highly influenced by both BD and MFA. Practical implication for hybridization among the three Eucalyptus species Hybridization between two different Eucalyptus species is one of the efficient techniques to improve the wood quality (Quilho et al. 2006, Grattapaglia and Kirst 2008, Clarke et al. 2009). In the present study, significant differences in growth characteristics and wood properties were found among the three species, and it is expected that both growth characteristics and wood properties could be improved by the hybridization among them. To evaluate these characteristics, scoring was given for superior characteristics based on the results of Tukey-HSD test on Table 2. Therefore, the superior group ( a or ab ) was scored 1 and the inferior group ( b ) was given score 0. In addition, total score was calculated for each category. The highest total score among the three species indicates that the tree species having a superior characteristic. The superior species in this study means species having desirable characteristics for lumber production (higher growth rate, higher wood density, higher strength properties, and others). The results of the growth characteristics showed that both E. grandis and E. pellita are superior (Table 4). In the wood properties, E. pellita is superior, followed by E. urophylla and E. grandis in the second and third positions, respectively. Therefore, it is considered that E. pellita is the superior species in both growth characteristics and wood properties. Table 5 provides growth conditions for the three Eucalyptus species based on the natural distribution and sites where these species successfully grow as exotics. E. urophylla naturally

9 Growth characteristics and wood properties of Eucalyptus planted in Indonesia 67 grows in Timor and other islands in the eastern part of the Indonesian archipelago. The altitude there ranges from 480 to 1250 m and the annual rainfall ranges 1000 to 1500 mm. E. grandis occurs naturally in Australia from Newcastle in New South Wales to southern Queensland with altitude m and average annual rainfall above 1000 mm. E. pellita has two natural occurrences: southern Papua New Guinea (lowlands, below 100 m altitude) and northern Queensland, Australia (approximately 600 m altitude). Table 4. Results of multiple comparison test and evaluation of growth characteristics and wood properties in three Eucalyptus species. Property E. urophylla E. grandis E. pellita D b (0) ab (1) a (1) TH b (0) a (1) a (1) Total score SWV a (1) a (1) a (1) BD a (1) a (1) a (1) MFA a (1) a (1) a (1) RS b (0) ab (1) a (1) TS b (0) a (1) a (1) CS a (1) b (0) ab (1) MOE a (1) b (0) ab (1) MOR a (1) b (0) ab (1) Total score Note: D, stem diameter; TH, tree height; SWV, stress-wave velocity; BD, basic density; MFA, microfibril angle; RS and TS, radial and tangential shrinkages per 1 percent change in moisture content, respectively; CS, compressive strength parallel to grain; MOE, modulus of elasticity; MOR, modulus of rupture, value in parentheses is group scoring. Scoring was given only for superior property based on Tukey-HSD test at 5 % level (Table 2). Thus, groups a and ab were given score 1, meanwhile group b has no score or 0. Total score indicates the degree of superiority on each category (growth characteristics or wood properties). Highest score is the best one. Based on this information, E. pellita can grow well under various conditions, especially in a wide range of altitudes. It also shows resistance to pests and diseases, and is tolerant to low soil fertility compared to the other two species. In the present study, no negative relationships were observed between growth characteristics and wood properties in the three Eucalyptus species (Fig. 6), suggesting that hybridization would produce a new generation of offspring with improved production volumes and timber quality. Considering such fast-growing characteristics with better wood properties, E. pellita is a first choice to be used for timber production and should be taken into account for improvement in tree breeding programs. In addition, due to the inferior wood properties in E. grandis, hybridization of E. grandis with E. urophylla or E. pellita might improve its wood properties, while it still has fast-growing characteristics and are better adapted to various environmental conditions, such as plantation altitude and rainfall (Table 5). Hybridization between E. pellita and E. urophylla should be of considerable interest. This hybrid might have the better growth characteristics of E. pellita (rapid growth rate, tolerance to infertile soil, resistance to pests and diseases, and a wide range of plantation altitudes) with the complementary, valuable wood properties of E. urophylla. However, the high T/R shrinkage ratio in E. pellita would be the main shortcoming in terms of lumber production for hybridization from this species. In this case, drying practices together with sawing methods should be integrated in timber quality improvement for this hybrid. CONCLUSION In the present study, growth characteristics and wood properties of three Eucalyptus species, E. urophylla, E. grandis, and E. pellita, planted for pulpwood in Indonesia, Table 5. Growing conditions for three Eucalyptus species. Parameter E. urophylla E. grandis E. pellita Altitude m m m 1, 3 Rainfall mm mm mm 1, 3 Pest/disease Susceptible 3 Susceptible 1, 3, 4 Resistance 1,3 Soil Tolerate to low fertility 3 Limited to high fertility and well-drained 1, 3, 4 Tolerate to low fertility 1, 3 Coldest-hottest temperatures Natural occurences Timor and eastern Indonesian archipelago 1 Clarke et al. (2009), 2 FAO (1979), 3 Harwood et al. (1997), 4 Listyanto et al. (2010) New South Wales (Australia) North Queensland (Australia) and southern Papua New Guinea

10 68 TROPICS Vol. 26 (2) Agung Prasetyo, Haruna Aiso et al. were evaluated for their possible utilization as timber. The results are as follows: 1) Significant differences both in growth characteristics and some wood properties were observed among the three Eucalyptus species, indicating that improvement of these values might be possible by hybridization between two species. 2) Among the three species, E. pellita has superior characteristics both in growth rate and wood properties. 3) No negative correlations were observed between growth characteristics and wood properties, suggesting that an improvement in wood properties (by selecting trees with existing superior wood properties) does not lead to a reduction in growth characteristics. 4) Hybridization between E. grandis and E. urophylla or E. pellita might improve the relatively lower wood properties of E. grandis. 5) Hybridization by using plus trees should be made between E. pellita and E. urophylla to produce trees with improvement on wood properties and growth characteristics. ACKNOWLEDGEMENTS The sample trees in this study were established by PT Toba Pulp Lestari Tbk in North Sumatra, Indonesia. The authors gratefully thank the company and staff for their support. We also express our sincere gratitude to Mr. P.A. Clegg for valuable suggestions and support during the field experiments. REFERENCE Andrade CR, Trugilho PF, Napoli A, Vieira RS, Lima JT, Sousa LC Estimation of the mechanical properties of wood from Eucalyptus urophylla using near infrared spectroscopy. Cerne 16: Barnett JR, Jeronimidis G Wood quality and its biological basis. CRC Press, Florida. Bhat KM, Bhat KV, Dhamodaran TK Wood density and fiber length of Eucalyptus grandis grown in Kerala, India. Wood and Fiber Science 22: Blackburn D, Hamilton M, Harwood C, Innes T, Potts B, Williams D Stiffness and checking of Eucalyptus nitens sawn boards: genetic variation and potential for genetic improvement. Tree Genetics and Genomes 6: Bosman MTM, Kort ID, Genderen MKV, Baas P Radial variation in wood properties of naturally and plantation grown light red meranti (Shorea, Dipterocarpaceae). IAWA Journal 15: Cademartori PHG, Missio AL, Gatto DA, and Beltrame R Prediction of the modulus of elasticity of Eucalyptus grandis through two nondestructive techniques. Floresta e Ambiente 21: Clarke B, McLeod I, Vercoe T Trees for Farm Forestry: 22 promising species. The Rural Industries Research and Development Corporation, Barton, Kingston. Dickson RL, Raymond CA, Joe W, Wilkinson CA Segregation of Eucalyptus dunnii logs using acoustics. Forest Ecology and Management 179: [FAO] Food and Agriculture Organization of the United Nations Eucalyptus for planting. FAO, Rome. [FWPA] Forests and Wood Products Australia Evaluation of wood characteristics of tropical post-mid rotation plantation Eucalyptus cloeziana and E. pellita: part (c) wood quality and structural properties: final report. FWPA, Victoria. Grattapaglia D, Kirst M Eucalyptus applied genomic: from gene sequences to breeding tools. New Phytologist 179: Gwaze DP, Bridgwater FE, Lowe WJ Performance of interspecific F 1 Eucalyptus hybrids in Zimbabwe. Forest Genetics 7: Harwood CE, Alloysius D, Pomproy P, Robson KW, Haines MW Early growth and survival of Eucalyptus pellita provenances in a range of tropical environments, compared with E. grandis, E. urophylla and Acacia mangium. New Forests 14: Hein PRG, Silva JRM, Brancheriau L Correlations among microfibril angle, density, modulus of elasticity, modulus of rupture, and shrinkage in 6-year-old Eucalyptus urophylla E. grandis. Maderas: Cieancia tecnologia 15 (2): Hung TD, Brawner JT, Mede R, Lee DJ, Southerton S, Thinh HH, Dieters MJ Estimates of genetic parameters for growth and wood properties in Eucalyptus pellita F. Muell. to support tree breeding in Vietnam. Annals of Forest Science 72: Ishiguri F, Aiso H, Hirano M, Yahya R, Wahyudi I, Ohshima J, Iizuka K, Yokota S Effects of radial growth rate on anatomical characteristics and wood properties of 10-year-old Dysoxylum mollisimum trees planted in Bengkulu, Indonesia. Tropics 25: Ishiguri F, Diloksumpun S, Tanabe J, Iizuka K, Yokota S Stress-wave velocity of tree and dynamic Youngʼs modulus of logs of 4-year-old Eucalyptus camaldulensis trees selected for pulpwood production in Thailand. Journal of Wood Science 59: Istikowati WT, Ishiguri F, Aiso H, Hidayati F, Tanabe J, Iizuka K, Sutiya B, Wahyudi I, Yokota S Physical and mechanical properties of woods from three native fast-growing species in a secondary forest in South Kalimantan, Indonesia. Forest Products Journal 64: Kollmann FFP, Côté WA Principles of Wood Science and Technology. Springer-Verlag, Berlin, Heidelberg, New York, Tokyo. Leksono B, Kurinobu S, Ide Y Realized genetic gains observed in second generation seedling seed orchards of Eucalyptus pellita in Indonesia. Journal of Forestry Research 13: Listyanto T, Glencross K, Nichols JD, Schoer L, Harwood C.

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