Heartwood proportion and density of Tectona grandis L.f. wood from Brazilian fast-growing plantations at different ages

The high demand for teak wood has driven efforts to achieve increased volumetric production in fast-growing plantations. However, the logs often exhibit higher proportions of sapwood and juvenile wood. This study was conducted to investigate how the age of teak trees in commercial plantations influences the heartwood proportion, wood density, and formation of mature wood. A total of 12 trees of both clonal and seed origins were harvested at the ages of 5, 10, 15, and 20 years old. Disks in the regions of the base, 2.3 m, and top of the trees were collected. Along the stem, we determined the total, heartwood, and pith diameters, as well as the proportions of bark, sapwood, heartwood, and pith. The base disks were used to analyze wood density and to demarcate the transition from juvenile to mature wood stages by X-ray densitometry. As teak wood aged, it exhibited higher heartwood percentages, with variations ranging from 7% (5 years old) to 56% (20 years old). The five-year-old wood had the mean highest density (0.74 g.cm⁻³). There was a trend of increasing mean wood density as the trees aged from ten years. The diameter profiles by X-ray densitometry indicate a higher wood density in the pith-bark direction. The density of 20-year-old wood ranged from 0.54 g.cm⁻³ (ring 1) to 0.78 g.cm⁻³ (ring 19). For all ages evaluated, juvenile wood is predominant, with the transition age occurring at approximately 11 years old. However, only 15- and 20-year-old trees had mature wood in their heartwood, but it was less than 2% of the total heartwood at those ages.