Decay evaluation of damaged beech trees (Fagus orientalis L.) adjacent to skid trails by nondestructive stress wave technique

Ground skidding damages the marginal trees of the skid trails and may decrease their growth increment at long period. In this research the effects of ground skidding on decay development and extent of the beech trees (Fagus orientalis Lipsky) adjacent to the skid trails, at four age classes, including: 0-5, 5-10, 10-15 and 15-20 year were investigated. After classifying the skid trails to three traffic levels, including: low, moderate and sever, depending on their distance to depot location and trails intersections, the time required for wave transit across the marginal trees at three directions, consisting of: wound direction, wound cross and stem longitudinal direction, was measured, using a stress wave velocity apparatus. After data correction by the apparatus correction coefficient, the tree’s stress wave velocity at the three directions were calculated then statistically analyzed. The results showed that more than 75% of the trees located at 1.5 m. distance adjacent to the skid trails, were wounded by the skidders which resulted in 25% decay. There was also not any decay in the unwounded trees adjacent to the skid trails. Therefore the decay extended when the age of the skid trails increased. Most of the decays were found at trees located at the skid’s trails curves and t down slopes. The results of this research demonstrate an irretrievable, but preventable damage to the standing trees within the skid’s activity extent.