Residual stand damage from cut-to-length thinning of a mixed conifer stand in northern Idaho

We collected residual stand-damage data from a mixed conifer stand in northern Idaho that had been commercially thinned with a cut-to-length harvesting system. The stand composition after harvesting was 76% grand fir (Abies grandis); 14% Douglas-fir (Pseudotsuga menziesii var. glauca); 5% western redcedar (Thuja plicata); and 5% lodgepole pine (Pinus contorta), western white pine (Pinus monticola), and ponderosa pine (Pinus ponderosa). For all crop trees, damage to the bole, roots, and crown was assessed using systematic sampling with a random start and fixed area plots. Wounding occurred on 37.4% of the remaining trees, but the severity of wounding varied significantly by species (P < 0.05). Eighty-four percent of wounding for all species combined was considered as small size (< 194 cm²). The greatest average amount of damage to a bole occurred along the first 2 m up from the ground (67.2%) and also within 4 m of the forwarder centerline (67.7%). Gouges were present on 41 % of all scars. Tree location to forwarder trail appears to have a significant effect on the number and height of scars on a tree (P < 0.05). We estimated that throughout a 20-year period, volume losses for grand fir because of decay would be 2.57% compared to 1.31% in an undamaged stand of similar composition.