Wood density of loblolly pine trees as affected by crown thinnings and harvest age in southern Brazil

摘要

The Brazilian plantation forestry is well known for high yields. Such yields are not necessarily linked with acceptable wood quality. Pine plantations are an important source of timber in Brazil, and although pulp and paper production plays a dominant role, there is an increasing need for sawtimber, and even high-quality timber is in demand. The impacts of crown thinning on ring width, ring density and juvenile-mature wood of loblolly pine trees were analysed. The experimental design included no thinning, an extreme release from competition, and two practice-oriented variants with moderate and heavy thinnings. X-ray microdensitometry provided ring width and density for 1197 rings and 44 trees. Mean ring width at 1.3 m height varied from 6 to 9 mm, reaching a maximum of 22 mm during the first 3-6 years regardless of thinning intensity. Only occasional differences were verified in ring densities produced from the different thinning variants. The transition from juvenile to mature wood occurred between 13 and 17 years of age. From the analysis of wood density, extreme and early thinning delayed the production of mature wood in 4 years compared with non-thinned or practice-oriented thinned stands. At the same harvest age, thinning had no effect on wood density. However, harvest age itself was a determinant for obtaining wood of higher density. Altogether, results indicated that regarding current market demands no constraints related to the analysed wood characteristics are to be expected, even if extreme thinning regimes are applied.