Radial Variation In Microfibril Angle Of Acacia Mangium
Abstract
Thirteen years old provenance trials of Acacia mangium from five provenances were established at five sites in the state of Sarawak , Malaysia, were sampled for this study. Fifty trees were sampled at random and cut to study radial variation in microfibril angle in the SS2 of secondary wall of the fibre using polarised microscope. Microfibril angle decreased from pith to bark with the greatest decrease occurred within the first two radial sampling near to the pith. It ranged from 5.9° to 28.8° with an overall mean and coefficient of variation of 12.6° and 45.8% respectively. It had a mean value of 21.4 at pith and 6.9 near the bark, which is a decrease of 67.8%. Highly significant different in mircrofibril angle were detected between radials of individual trees at α≥0.001. It was the major contributors to the total variance in which contributed for about 64.8%. Variations between trees were highly significant at α≥0.001 and accounted for 25.5% of the variation in micro fibril angle while differences between the two orientations were not significant at α≤0.05.
Keywords
Download Options
Introduction
In future, it is expected that Malaysian and international market will be flooded with wood produced by short rotation fast growing timber species. A major concern with short rotation is the present of higher proportion of juvenile wood known as core wood (Burdon et al. 2004). Juvenile wood displays poor characteristics like higher microfibril angle (MFA), lower density, low stiffness, thinner cell walls, and shorter tracheids than mature wood (Cown 1992). Lower densities and reduced fibre dimensions, higher MFA, and low stiffness of juvenile woods are expected to produce a poorer quality product, often causing dimensional instability, for example in loblolly pine (Kretschmann and Bendtsen 1992) and Sitka spruce (Macdonald and Hubert 2002), resulting in poor acceptance in the market (Cown and van Wyk 2004). For these reasons, wood property traits have begun to receive more attention in the tree improvement programs as well as in forest industry (Powell et al. 2004).
In addition to specific gravity the other most important wood characteristic, which has direct impact on wood stiffness and strength, is microfibril angle (Butterfield 1998; Bendtsen and Senft 1986; Cave 1969). It also has an influence on shrinkage of wood (Harris and Meylan 1965; Ying et al. 1994). Microfibril angle (MFA) is referred to the mean helical angle that the cellulose microfibril in the S 2 layer of the cell wall makes with the longitudinal axis of the cell (Barnett & Bonham 2004). Microfibril angle is a property of the cell wall of wood fibers, which is made up of millions of strands of cellulose called microfibril (Walker & Butterfield 1995 and Butterfield 1998).
Now in Malaysia as Acacia mangium is gaining popularity for both timber and for pulping, understanding the wood properties of this species is particularly important to effectively utilize this timber and before any improvement program has been developed to improve its quality. This study was therefore carried out to fulfil this objective. The work described in this paper forms part of a larger study of the genetic and environmental influences, and their interaction on growth, wood properties and mechanical properties in Acacia mangium. The main objective of this study is to establish a radial variation in MFA and to study the extent of variations in microfibril angle between trees, orientations and radial subsamples.
Conclusion
All trees exhibited the same decreasing pattern of microfibril angle radially from pith to bark. The largest decrease occurred in the first two sub samples from pith followed by a gradual decrease in the last two sub samples towards bark. Radial variation in microfibril angel is the most important factor affecting variation in MFA. It accounted for 61% of the total variation. Variation between trees is substantial and contributed for 22.3% of the total variation. Although this variation is only one third of the radial variation, it provides a basis for an improvement in MFA hence the wood strength in Acacia mangium .