Density Results and Discussion

12 Figure 6 Average density values from pith to bark of sengon a, jabon b, douglas-fir c and poplar cultivars d The result on Figure 6d show that the average density of poplar cultivars tend to slightly fluctuated from pith to bark. It was due to veneers samples were collected up to core diameter of 14 cm. The average wood density near pith were 390 kgm -3 ‘lambro’, 522 kgm -3 ‘soligo’, 291 kgm -3 ‘I214’ and 353 kgm -3 ‘koster’, respectively. Wood density near bark were 379 kgm -3 for ‘lambro’, 445 kgm -3 for ‘soligo’, 418 kgm -3 for ‘I214’ and 322 kgm -3 for ‘koster’. Nurbaiti 2012 declared that the average density of ‘lambro’, ‘soligo’, ‘I214’ and ‘koster’ are 380 kgm -3 , 370 kgm -3 ,300 kgm -3 and 370 kgm -3 , respectively. In the current study, since density near the pith was lower than that near the bark for sengon, jabon, douglas-fir and poplar cultivars, attention should be given for the utilization of these woods in certain wood-processing technologies, e.g. production of sawn timber, drying, plywood and laminated veneer lumber. These results correspond with results of Bendtsen 1978 who reports that specific gravity or density, cell length, strength, cell wall thickness, transverse shrinkage and per cent latewood increase towards the bark, while microfibril angle, longitudinal shrinkage and moisture content decrease. It could be considered that the density behavior from pith to bark of fast growing species not only happened on intensively-managed stands but also unmanaged community forest in Indonesia and in France. When segmented regression models were applied, it was deduced that the use of density was not appropriate because of low coefficients of determination and large range of ages for transition from juvenile to mature wood. Thus, density 200 400 600 5 10 15 20 Den sity kg m -3 Segmented rings from pith to bark Sengon 5 years Sengon 6 years Sengon 7 years 200 400 600 800 5 10 15 20 Den sity kg m -3 Segmented rings from pith to bark Jabon 5 years Jabon 6 Years Jabon 7 years a b 200 400 600 800 1000 1200 5 10 15 20 25 Den sity kg m -3 Segmented rings from pith to bark Douglas-fir 26 years old 200 400 600 800 5 10 15 20 25 30 Den sity kg m -3 Segmented rings from pith to bark Lambro 18 years Soligo 18 years I214 18 years Koster 18 years c d 13 could not be considered as a suitable parameter for determining demarcation point of sengon, jabon, douglas-fir and poplar cultivars. The same result was observed by Darmawan et al. 2013 who find density trend from pith to bark was also not suitable for determination of transition age between juvenile and mature wood of 7 years old sengon and jabon. On the contrary, the value of ring density and ring area can be used to determine the transition age on black spruce Picea mariana Alteyrac et al. 2006.

2.4.2 Fibre length

Average fibre length at dbh from pith to bark is presented in Figure 7a-d. The coefficient variations of fiber length values in each segmented rings were observed to be less than 10 for all wood species. The highest value of fibre length was at near the bark. In sengon 5, 6 and 7 years old, average fibre lengths of the first to third segmented rings began from less than 1 mm while in the fourth ring onwards, they exceeded 1000 µm Figure 7a. In jabon 5, 6 and 7 years old, the average fibre lengths of the first to second segmented ring began from less than 1 mm, while, starting from the third ring, the lengths exceeded 1000 µm Figure 7b. Figure 7 Average fiber length values from pith to bark of sengon a, jabon b, douglas-fir c and poplar cultivars d 400 1400 2400 10 20 30 40 Fib er len gth µ m Segmented rings from pith to bark Lambro 18 years Soligo 18 years I214 18 years Koster 18 years 400 1400 2400 5 10 15 20 Fib er len gth µ m Segmented rings from pith to bark Jabon 5 years Jabon 6 years Jabon 7 years d b 400 1400 2400 5 10 15 20 Fib er len gth µ m Segmented rings from pith to bark Sengon 5 years Sengon 6 years Sengon 7 years a 400 1400 2400 3400 4400 5 10 15 20 25 Fib er len gth µ m Segmented rings from pith to bark Douglas-fir 26 years c 14 Sengon and jabon of 5, 6 and 7 years old still showed gradual increase in fibre length until near bark. Shorter fibre length near pith is caused by accelerated rate of anticlinal division in fusiform initial cell while longer fibre length near the bark is due to this rate slowing down Panshin and de Zeuw 1980. Further, average fibre lengths at the dbh from pith to bark for sengon at the age of 5, 6 and 7 years were 1131, 1170 and 1147 μm, respectively, for jabon 5, 6 and 7 years were 1190, 1245 and 1224 μm, respectively. These results also correspond with results from Kiaei et al. 2012 who find that fibre length of Acer velutinum increase along the radial direction from pith to bark. The proportional increase of fibre length from pith to bark proved fibre length as a reliable indicator of the juvenile wood presence. Douglas-fir produced longer average fiber length from pith to bark compare to other species in this study. The average fiber length value for 26-years old Douglas fir was 3177 µm Figure 7c. It correspond to the results presented by Martin et al. 2006, who discovered that the average fiber length of 31 years old Douglas fir is 3360 µm. Figure 7d also shows that ‘koster’ had fiber length less than 1 mm from the first to third segmented rings. The other cultivars had more than 1000 µm of fiber length starting from the first segmented rings. Poplar cultivars did not show gradual increase in fiber length from pith to bark. The average fiber length for ‘lambro’, ‘soligo’, ‘I-214’ and ‘koster’ were 1097, 1311, 1306 and 1403 μm, respectively. These results corresponded to Panshin and de Zeuw 1980 who reported that the poplar fiber length are in range from 1320 and 1380 μm. However, these results did not correspond to Berthelot et al. 2013 who find the average of fiber length for ‘lambro’, ‘soligo’, ‘I-214’ and ‘koster’ were 853, 867, 868 and 979 μm, respectively. The higher values of fiber length from these results were due to the samples were taken after log diameter of 14 cm, otherwise Berthelot et al. 2013 use the samples from pith to bark. Douglas-fir softwood had the longest fiber length, then followed by jabon, poplar cultivars and sengon belongs to hardwood. This is in line with Bowyer et al . 2005 who state that hardwood fibers are shorter than softwood tracheids. These differences gave an indication that the tree species in this study would have different impacts on their utilization. Segmented regression analysis suggested that fibre length was an appropriate trait to determine the demarcation point from juvenile to mature wood in sengon, jabon, poplar cultivars and douglas-fir. The demarcation point according to the fibre length values are presented in Table 3. Using segmented regression analysis, we concluded that juvenility of 5, 6 and 7 years old sengon occurred until the 17 th , 17 th and 16 th ring while that of jabon occurred until the 24 th , 23 rd and 21 st rings. Therefore, based on fibre length trait, we concluded that 5, 6 and 7 years old jabon and sengon were all juvenile. These results suggested that the mature wood for sengon would be occurred after dbh 34 cm and for jabon would be occurred after dbh 48 cm. Unfortunately, sengon and jabon in Indonesia are felled at the ages between 5 and 7 years because the dbh of about 35 cm is large enough for wood industry and selling at shorter cycle will mean more income for the communities.