Variation of transition ring with traits

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 19 the MOE and MOR results in this work are within the range reported in that literature. The behaviors of density, fiber length, MFA and strength values of sengon and jabon wood obtained in this study were expected to provide practical information for processors and silviculturists of sengon and jabon, leading to a more appropriate usage of these species. The presence of juvenile wood has to be taken into consideration with respect to the use of sengon, jabon, douglas-fir and poplar cultivars for construction purposes particularly when bending and dynamic strength properties are critically important factors. Lower strength properties of juvenile wood imply that strength properties of sengon, jabon, douglas-fir and poplar cultivars trees depend on their juvenile wood contents. Thus, timber with large percentages of juvenile wood, especially from fast growing trees, will be less desirable for solid wood products. Several studies completed on solid-sawn lumber have provided a good understanding of how juvenile wood affects the mechanical properties of solid-sawn lumber Biblis 1990; Kretschmann and Bendtsen 1992; MacPeak et al. 1990. Considering efficiency in utilizing fast growing timber, reducing the volume of juvenile wood would be beneficial. There are long- and short-term alternative solutions for reduction of juvenile wood proportion. The former would include genetic and silvicultural treatments while the latter, improvement in wood utilization methods, e.g. producing laminated veneer lumber from fast growing species which will help solve problems linked to shrinkage of raw material for construction and protection of natural forest. Moreover, the shapes of fast growing species logs round, straight and cylindrical also become supporting factor in peeling process. However, a major problem in the production of laminated veneer lumber is ensuring veneer surface quality whereby advanced research is needed to optimize peeling process of logs containing large amounts of juvenile wood.

2.5 Conclusion

Results of segmented regression analysis on fibre length and microfibril angle showed different results for transition age at dbh. The demarcation point transition age between juvenile and mature wood was dependent on the traits or parameter used. According to fiber length and MFA traits, transition age of 5, 6 and 7 years old of sengon and jabon were occurred ranging from 17 to 18 segmented ring and ranging from 18 to 20 segmented ring, respectively. The transition age of poplar cultivars and douglas-fir, occurred from 12 based on fiber length and 13 years old based on MFA and occurred from 18 based on fiber length and 20 years old based on MFA, respectively. The portions of juvenile wood both in sengon and jabon at dbh at the age of 5, 6 and 7 years old were 100 . Poplar cultivars and douglas-fir contained 52 and 77 of juvenile wood portion, respectively. Fibre length and microfibril angle appeared to be the best anatomical indicators of demarcation point between juvenile and mature wood compare with density in this study. Segmented regression analysis proved to be a practical and objective method to estimate demarcation point transition age between juvenile and mature wood in sengon, jabon, poplar cultivars and douglas-fir. 20 The demarcation point transition age of sengon, jabon, poplar cultivars and douglas-fir wood obtained in this study were expected to provide practical information for industries and silviculturists of these species. This would eventually provide more appropriate utilization of these species especially for construction purposes. Lower density and static bending strength MOEMOR of the juvenile wood at the age of 5, 6 and 7 years suggested that both sengon and jabon plantation forest can be manipulated effectively through appropriate management practices e.g. longer rotation age to reduce juvenile wood content. Because timber with large percentage of juvenile wood, especially from fast- growing trees, will be less desirable for solid wood products.