| Summary: | <p><em>Aim of the study: </em>The aim of the study is to assess the variation of pith eccentricity, heartwood proportion, latewood percentage and basic wood density along the stem of 45-year-old <em>A. melanoxylon </em>trees collected in four sites of Portugal, and investigate the eventual relationship between these variables.</p><p><em>Area of study: </em>Sites covering littoral north, mid interior north and centre interior of Portugal.</p><p><em>Materials and methods: </em>Four sites and five trees per site were selected in the <em>Acacia melanoxylon </em>Portuguese forest.</p><p>One wood sample at each of six height levels per tree was collected in order to evaluate its basic density, pith eccentricity, heartwood and latewood proportions.</p><p><em>Main results: </em>The high variability of the wood macroscopic properties among trees from the same site regarding to the variation of the corresponding average properties along the stem is a key characteristic of the experimental data.</p><p>As a consequence, a multiple linear regression model tested was not able to properly explain the wood basic density variation of the 120 wood samples analysed. In spite of this, the following trends could be recognized: (i) excluding the base level, wood basic density moderately increased with tree level; (ii) latewood proportion followed similar behaviour; (iii) pith eccentricity was low; (iv) heartwood proportion decreased markedly with tree height, from 70% at the base to 7% at the top.</p><p><em>Research highlights: </em>The high basic density, the relatively low variability along the stem and the low pith eccentricity enable us to anticipate good performance as raw material for the wood industry.</p><p><strong>Key words</strong>: <em>Acacia melanoxylon; </em>basic density; earlywood; latewood; heartwood; sapwood; pith eccentricity.</p>
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