Damage characteristics in young Douglas-fir stands from commercial thinning with four timber harvesting systems

Damage to residual trees from commercial thinning was characterized and compared among four common harvesting systems in western Oregon: tractor, cut-to-length, skyline, and helicopter. Six young (30- to 50-yr-old) Douglas-fir (Pseudotsuga menziesii) stands with various residual densities were studied: Scarring was the most typical damage to crop trees, accounting for 90% of the total damage in most cases. Damage levels greatly decreased as the minimum scar size that defines damage was increased. Scarring by ground-based systems was more severe: scars were larger, and gouge and root damage were more prevalent than in skyline and helicopter systems. Damaged trees were concentrated within 15 ft of skid trails or skyline corridor centerlines. In the cut-to-length system, the harvester caused more wounding (70%) to crop trees than did the forwarder (30%), but forwarder scars were larger and sustained severe gouging. Recommendations for minimizing stand damage are included.