Abstract
In this study, several wood properties were investigated along with the longitudinal direction for oriental beech and caucasian fir trees grown in Turkey. Wood density, compression strength parallel to grain, chemical characteristics (holocelluose, celluose, lignin), fiber dimensions (fiber length, fiber width, fiber lumen width, fiber cell wall thickness) were measured from the sapwood of the discs taken at the stem heights of 1.30, 6.30 and 12.30 meters. Both wood species showed clear trends in wood properties along longitudinal direction. For both wood species, the highest values in density, compression strength, volumetric shrinkage and swelling were at 1.30 m stem height, and the investigated paraeters decreased along with the stem height, while longitudinal shrinkage and swelling percentage increased. The highest cellulose content was found at 1.30 m stem height, and the highest lignin content was found at 12.30 m stem height for both wood species. The longest fibers and the thickest fiber walls were determined at 1.30 m stem height in both wood species. These results clearly indicated that stem height greatly affected the investigated wood properties for both wood species.
Highlights
The importance of variability in wood properties within tree has often been emphasized in the literature
Compression strength, shrinkage and swelling percentage except for longitudinal shrinkage and swelling percentage decreased clearly from 1,30 m to 12,30 m stem height and the difference among stem heights was significant for both wood species
The content of lignin increased while the content of cellulose decreased along the stem height in both wood species
Summary
The importance of variability in wood properties within tree has often been emphasized in the literature. Zobel and van Buijtenen (1989), the most important reference on this subject, explained in detail the changes in a number of wood properties both radial (from the center to the bark) and longitudinal (from the base to the top) direction in the tree. The recent work of Kiaei and Farsi (2016) for Persian silk wood (Albizzia julibrissin) illustrated wood density, modulus of elasticity and modulus of rupture in bending decreased from base to top with height, and Longui et al (2016) for Astronium graveolens showed specific gravity was higher at the base of tree and shear parallel to grain did not vary in analyzed heights. When the publications are examined, it is seen that there are more studies in conifers than hardwoods. Machado and Cruz (2005) determined a decreasing tendency of mechanical properties (bending strength, modulus of elasticity parallel to grain, compression strength parallel to grain, tension strength perpendicular to grain) of maritime pine because of the growing presence of juvenile wood. Molteberg and Høibø (2006) found that fiber width decreased, while basic density and fiber length of norway spruce increased with increasing height in the tree. Cato et al (2006) stated that wood from
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