Tree Age and Size Affect Selected Fiber Parameters in Black Locust (Robinia pseudoacacia L.) Wood

The study investigates selected parameters describing the fibers of black locust (Robinia pseudoacacia L.) wood with regard to tree age and size (diameter). The material was collected in stands aged 38, 60, and 71 years growing on the mesotrophic sites in southwestern Poland. In each stand, we sampled trees from three diameter classes (thin, medium, and thick specimens). From each tree, we took two 20 mm × 20 mm × 30 mm wood samples, from which we cut slices from the tangential plane using a sliding microtome. The Olympus cellSens Standard software was used to take pictures of 15 fibers per sample. In total, studies were carried out on 510 fibers. We measured fibers’ dimensional parameters (length, diameter, lumen, and wall thickness) with ImageJ 1.8.0 software and, based on these, we calculated the fiber shape coefficients (slenderness ratio, rigidity index, Runkel ratio, flexibility coefficient, Mühlsteph index, and solids index). Both the age and size of trees significantly influenced the examined parameters of black locust fibers, with the single exception of fiber lumen, which was dependent only on tree age. In general, the examined age classes differed one from another, while, in the case of tree size, significantly different values were usually only found for the thinnest trees. Our results suggest that wood of medium-thick, medium-sized, or older black locust trees seems to be the most appropriate raw material for paper or pulp production, as it has the least variability in the analyzed features. The wood of the youngest trees would be potentially the least useful for these applications.