Factors influencing residual stand damage levels due to cable thinning of coniferous stands in western Oregon

Abstract

The purpose of this study was to determine the significant variables influencing the damage levels sustained by the residual stand after skyline thinning of coniferous stands. Damage levels were measured in ten study areas in western Oregon that had received their first commercial thinning. For this post-logging study, 38 units consisting of one side of a corridor were chosen. Damage levels and characteristics of stand damage were measured using a transect method designed to account for the high variability in the distribution of damaged trees. Ten independent variables were measured in three categories: harvesting system, stand conditions and topography. Total scar area per acre (ft2 /acre) was used as the dependent variable to indicate the damage level. As a result of regression analysis, three variables were shown to be significant. These variables are the percent of western hemlock in the stand, the volume removed per acre (ft3/acre) and whether the unit had been logged conventionally or by prebunching and swinging. Damage levels ranged from 0.4 to 64.4 square feet of scar area per acre. Individual scars ranged in size from 0.02 to 12 square feet. This paper provides an indication of the important variables influencing stand damage levels including several variables that could not be incorporated in the regression equation due to statistical limitations. Information on some of the characteristics of stand damage such as location of damaged trees with respect to the corridor and damage types is also included.