Microfibril angle Results and Discussion

16 average 65° and near bark, from 28° to 35° average 32°. Microfibril angles of 6-year-old jabon varied from 54° to 72° average 62° near pith and from 27° to 32° average 30° near bark. Microfibril angles of 7-year-old jabon near pith varied from 56° to 67° average 62° and from 22° to 29° average 26° near bark. Figure 8a-b shows the demarcation point between juvenile and mature wood began at segmented ring-18. Figure 8 Average MFA values from pith to bark of sengon a, jabon b, douglas-fir c and poplar cultivars d Microfibril angle of douglas-fir decreased from pith to bark Figure 8c. Microfibril angle values near pith reached 77°. After the 15 th segmented rings, MFA values decreased until less than 30°. The results in Figure 8c show that douglas-fir MFA would be constant at values less than 30°. MFA values near pith varied from 54° to 78° average 64° and near bark from 27° to 28° average 28° Figure 8c. The same trend was also observed on poplar cultivars. Microfibil angle declined towards the bark. Microfibril angle values near pith reached more than 60°, after the 15 th segmented rings, MFA values decreased until less than 20°. The results in Figure 6d show that MFA for all poplar cultivars would be constant at values less than 20°. MFA values near pith for ‘soligo’ varied from 35° to 59° average 43° and near bark from 16° to 19° average 17° Figure 8d. ‘Koster’, varied from 30° to 50° average 36° near pith and near bark from 16° to 17° 20 40 60 80 5 10 15 20 MFA ° Segmented rings from pith ro bark Jabon 5 years Jabon 6 years Jabon 7 years b 20 40 60 80 5 10 15 20 MFA ° Segmented rings from pith to bark Sengon 5 years Sengon 6 years Sengon 7 years a 20 40 60 80 5 10 15 20 25 MFA ° Segmented rings from pith to bark Douglas-fir 26 years c 10 30 50 70 5 10 15 20 25 30 MFA ° Segmented rings from pith to bark Lambro 18 years Soligo 18 years I 214 18 years Koster 18 years d 17 average 17° Figure 8d. ‘I 214’ varied from 35° to 61° average 44° near pith and near bark from 16° to 20° average 18° Figure 8d. ‘Lambro’, varied from 35° to 58° average 43° near pith and near bark from 17° to 20° average 18° Figure 8d. All of these results correspond with the results presented by Bendtsen 1978 who found that softwood microbril angle decrease from pith towards bark. The estimation of demarcation point transition age between juvenile and mature wood according to microfibril angle are presented in Table 3. Based on segmented regression approach, we concluded that juvenility of 5, 6 and 7 years old of sengon occurred until 19 th , 17 th and 18 th segmented rings, respectively. Juvenility for jabon were at the 24 th 5 years old, 22 nd 6 years old and 19 th 7 years old segmented rings. Based on the microfibril angle values, we concluded that 5, 6 and 7 years old sengon and jabon were near all juvenile wood. We estimated that the diameter size of sengon and jabon stems which contained mature wood occurred after dbh 38 cm and after dbh 48 cm, respectively. According to segmented regression analysis, we concluded that juvenility of ‘soligo’, ‘koster’, ‘I214’ and ‘lambro’ occurred up to the 18 th , 19 th , 17 th and 19 th segmented rings, respectively. Juvenility for douglas-fir occurred up to the 21 st segmented rings. We concluded that the average transition age of poplar cultivars happened after 18 th segmented rings. Transition age of 26-year-old douglas-fir occurred after 21 st segmented rings. We estimated that transition age between juvenile and mature wood of poplar and douglas-fir stems ocurred after 13 years old and 21 years old, respectively. Microfibril angles affect the dimensional stability of wood. Greater microbril angle can cause greater longitudinal shrinkage Panshin and de Zeuw 1980, Tsoumis 1991, Bowyer et al. 2007. In order to minimise the juvenile wood proportion, we could suggest that silvicultural treatments such as fertilisation and irrigation were not applied especially in early growth years.

2.4.4 Variation of transition ring with traits

The demarcation point transition age for wood species were calculated based on fiber length and MFA, using segmented regression analysis, as described above. The segmented regression analysis applied to the two traits fiber length and MFA, led to different results for transition age at the 1.3 m sampling height Table 3. The difference between the traits was not remarkable. The results showed that transition age determined from MFA was 1 –3 segmented rings higher than transition age determined from fiber length. This analysis confirms that the determination of transition age was dependent on the trait considered. Although fiber length and MFA have different radial patterns, the transition age values found by the two traits were not significantly different. The variations in fiber length and MFA in temperate woods have been extensively characterized in many species, especially in pine. The commercial importance of fiber length and MFA, as it relates to wood quality, is well established for temperate woods, but is less clear for tropical woods. Relatively few tropical woods have been characterized, so there is a need to extend the range of species and ecotypes that have been investigated. Additionally, more well- designed studies relating fiber length and MFA and its interaction with other wood properties to timber quality are needed. Finally, the means through which trees 18 control changes in fiber length and MFA in response to developmental and environmental influences are poorly understood. The behaviors of MOE and MOR from pith to bark for sengon and jabon are presented in Figure 9a-d. The results indicated that wood near pith of sengon and jabon had lower MOE and MOR values than wood near the bark. The lower MOE and MOR of wood near pith were due to larger microfibril angle and lower density. However, the proportional increase of the MOE and MOR from pith to bark precludes the use of MOE and MOR as a reliable juvenile wood presence indicator. Figure 9 Average values from pith to bark of sengon MOE a, jabon MOE b, sengon MOR c and jabon MOR d Mean MOE values from pith to bark for 5, 6 and 7 years old sengon wood were 4780, 5573, and 4867 MPa, respectively. The mean MOR values from pith to bark were 37 MPa 5 years old, 38 MPa 6 years old and 36 MPa 7 years old. Mean MOE values from pith to bark for 5, 6 and 7 years old jabon wood were 4951, 5638, and 5642 MPa, respectively. The mean MOR values from pith to bark were 45 MPa 5 years old, 46 MPa 6 years old and 49 MPa 7 years old. Martawijya et al. 2005 found out that the MOE and MOR of sengon are 4450 MPa and 32 MPa, respectively, and that of jabon are 5545 and 39 MPa, respectively. However, the average strength values in this reference was without any information whether the samples from juvenile or mature wood. Fortunately, 20 40 60 80 1 2 3 4 5 6 7 8 MO R MP a Segmented rings from pith to bark Jabon 5 years Jabon 6 years Jabon 7 years d 3000 4500 6000 7500 9000 1 2 3 4 5 6 7 8 MO E MP a Segmented rings from pith to bark Sengon 5 years Sengon 6 years Sengon 7 years a 20 40 60 80 1 2 3 4 5 6 7 8 MOR MP a Segmented rings from pith to bark Sengon 5 years Sengon 6 years Sengon 7 years 1500 3000 4500 6000 7500 9000 1 2 3 4 5 6 7 8 MO E MP a Segmented rings from pith to bark Jabon 5 years Jabon 6 years Jabon 7 years b c