Arkadiusz Tomczak


The technical value of wood is high if the strength and density ratio is high. Theoretically this means that high strength and low density material will offer higher technical value. The strength and density ratio is referred to as the strength quality coefficient. It is the basis for comparing various materials. The author analysed the axial variability of the strength quality coefficient when fibres are compressed lengthwise and when juvenile wood is statically bent. Therefore, the study related to wood obtained at various stages of tree life.
The research material was collected from 72 trees growing in 8 mature pinewood stands. The value of the strength quality coefficient when compressed along fibres (Jz) was calculated with reference to 1,320 samples while the value for static bending (Js) with reference to 1,281 samples. Each pool of data was divided into sub-pools in line with the adopted longitudinal cross section of the trunk. The first sub-pool represented the breast height diameter. The location of the subsequent sub-pools was identified with reference to relative values by making marks corresponding with 20, 40, 60 and 80% of the tree height.
The average value of the strength quality coefficient for compression along fibres amounted to 5.37 km while for static bending it amounted to 10.97 km. For compressing and bending alike, the coefficients grew from the breast height diameter to a level representing 40% of the tree height. Once this threshold was crossed, the coefficients tended to decrease and reached the lowest value at the level located closest to the tree top. The most valuable juvenile wood was detected between 20 - 40% of the tree height. These are the height brackets where the trunk is exposed to extremely intense stresses resulting from, for example, wind and the location where wood tends to break most frequently.


resistance to compressing along fibres, resistance to static bending, wood density, tree biome-chanics

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Forestry Letters  eISSN 2450-4920

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