Physical properties of juvenile fir-wood [Abies alba Mill.) from Gorski Kotar

Felling of small-diameter trees has posed a threat to fir (Abies alba Mill.) in the Gorski Kotar region. In logs obtained from small-diameter trees the share of juvenile wood has been increasing. It is therefore important to be aware of juvenile fir-wood properties in order to be able to define the processing modes. This research has covered the properties of ring width, oven dry wood density, basic density, longitudinal, radial, tangential and volumetric shrinkage, and fiber saturation point for juvenile and mature fir-wood. The research has been carried out on ten fir trees at breast height (breast height diameter being 25-30 cm for four trees, 31-40 cm for two trees, 41-50 cm for two trees, 60 cm and more for two trees). Juvenile and mature wood were distinguished on the basis of the radial shift in the trend of physical properties distribution. Such a method does not grant the establishment of a firm line between juvenile and mature wood. Juvenile fir-wood covers the inner part of a trunk, 30-40 rings from the pith. This has been concluded on the basis of the radial shift in ring width distribution trend, in density of oven dry wood and in tangential and volumetric shrinkage trends. The other physical properties have been neglected in final consideration because of the great variation in data. Under the assumption that juvenile wood encompasses the thirty innermost rings, the density of oven dry wood mean value is 0.3976 g/cm3 for juvenile wood and 0.4977 g/cm3 for mature wood; the tangential shrinkage mean value is 7.7% for juvenile wood and 8.8% for mature wood; the volumetric shrinkage mean value is 11.8% for juvenile wood and 13.6% for mature wood. If juvenile wood is assumed to spread over the forty innermost rings, the mean values are: 0.4083 g/cm3 (juvenile wood) and 0.4512 g/cm3 (mature wood) for oven dry wood density; 8% (juvenile) and 8.9% (mature) for tangential shrinkage; 12.3% (juvenile) and 73.7% (mature) for volumetric shrinkage. It can be generally stated that juvenile fir-wood has larger ring breadth, lower oven dry wood density, lower tangential shrinkage and lower volumetric shrinkage than mature fir-wood.