Abstract

SANTOS, António et al. Wood Potential Use of Acacia melanoxylon Growing in Pure or Mixed Stands with Pinus pinaster by the Portuguese Forest Industry . Silva Lus. [online]. 2007, vol.15, n.1, pp.57-77. ISSN 0870-6352.

Acacia melanoxylon R. Br. (Blackwood) grows well in Portugal, in pure or mixed stands with Pinus pinaster Aiton though it faces strong ecological and legal constraints. In spite of some difficulties, for instance with drying, Blackwood timber is used for furniture and craft wood products due mainly to its texture and dark colour. It can also be used for pulp, being planted in many countries for that purpose along with Acacia mangium and A. dealbata. Its pulping and paper making potential have been studied by several authors (Clark et al., 1991; Guigan et al., 1991; Furtado, 1994; Gil et al., 1999; Paavilainen, 2000; Santos et al., 2002; Santos et al., 2006). Forest industry in Portugal depends strongly on maritime pine and eucalypt, with the consequent negative competition between the various industries for the same raw material. In Portugal there are many spontaneous stands with Acacia species, namely A. dealbata and A. melanoxylon. While A. dealbata species is considered a problem (at ecological level), A. melanoxylon is well adapted to Portuguese conditions. Therefore, it should be considered as an alternative raw material for sawmills and pulp industry and can prevent large monoculture areas therefore minimizing the risk of fire. Diameter annual increment of acacia (0.89 cm.ano^-1) exceeds maritime pine (0.58 to 0.85 cm.ano^-1) (Tavares et al., 2004) and comes close to eucalypt (0.84 to 0.96 cm.ano^-1) (Tomé et al., 2001). Acacia solid wood properties (Average density ± sd - 650 kg.m^-3 ± 75, Average bending strength ± sd - 146 N.mm^-2 ± 24, Average modulus of elasticity ± sd - 14200 N.mm^-2 ± 2160 and Average axial compression strength ± sd - 61 N.mm^-2 ± 7) allow this species to be considered as an alternative to maritime pine (630 kg.m^-3 ± 75, 130 N.mm^-2 ± 33, 10500 N.mm^-2 ± 3590 and 47 N.mm^-2 ± 10) (Machado e Cruz, 2005). Maritime pine and acacia woods can be, in general, classified as light to medium density showing medium strength and stiffness. Maritime wood pine quality shows a high variability being its potential claimed from data obtained from high quality forest stands (Machado e Cruz, 2005). Concerning papermaking potential, at a given drainage resistance (30 ºSR), the papers produced with acacia present higher apparent densities than eucalypt (0.80 to 0.66 g/cm³) (Santos et al., 2004). This is due to the lower coarseness and higher flexibility and collapsibility of its fibers (Santos et al., 2006). Despite the slightly higher fiber length, this fiber leads to papers with good relationship of light scattering and smoothness, together with good tensile strength and at low refining energy consumption. This behavior demonstrates that acacia fibers show an interesting potential use, at least in conjunction with eucalypt fibers for writing and printing paper. This paper concerns analysis of acacia's potential as raw material source for Portuguese industry (as solid wood and pulp and paper), getting together information from forest management, wood and fiber quality. It will be using knowledge acquired from previous research projects and preliminary results from an ongoing research on A. melanoxylon from mixed (with P. pinaster) or pure stands in the north of Portugal.

Keywords : Acacia melanoxylon; Pinus pinaster; Eucalyptus globulus; growth; solid wood; papermaking.

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