Damage to young Douglas-fir stands from commercial thinning with various timber harvesting systems and silvicultural prescriptions: Characteristics, sampling strategy for assessment and future value loss

Understanding the impact of thinning on residual stands helps forest managers achieve management objectives associated with sustainability and quality control. Stand damage control becomes more critical as thinning prescriptions in the Pacific Northwest are increasingly required for intensive management of second-growth young stands. The purpose of this study was to describe damage characteristics caused by various thinning systems, to recommend the best sampling strategy, and to estimate logging damage impact on future timber value.; For all logging systems, scarring was the most typical type of damage to crop trees, accounting for more than 90% of the total damage in most cases. Damage was concentrated along the skid trails or the skyline corridors. Harvesters caused more damage (70%) to crop trees in the cut-to-length thinning than did forwarders (30%). Damage levels dropped drastically when larger minimum scar sizes were applied. Damage levels were also greatly influenced by one or more compounding variables such as skid trail width, so that there was no specific relationship between damage level and logging systems.; Systematic plot sampling consistently provided estimates similar to the results of a 100% survey. This method also took the least amount of time and effort to lay out on the map and to locate plots in the field. An easy, quick survey method was proposed to monitor residual stand damage for in-progress and post-thinning operations. A quick assessment of damage allows forest managers to control stand damage in current thinning operations and also to determine whether detailed sampling is required for further investigation.; All scars that remained open in western hemlock and Sitka spruce sustained advanced decay during the 13 years after initial wounding. Scars less than 10 cm (4 in.) in width were closed in 8 years. Douglas-fir was more resistant to decay, and no rotting was observed in scars less than 21 years old. Advanced rotting and pitch ring defects, however, were observed in 29-year-old scars, both open and closed. Because of these defects, future value loss increased with time after wounding and with higher damage levels. Value loss can justify increased thinning costs incurred for minimizing stand damage.