Soil Compaction and Visual Disturbance Following an Integrated Mechanical Forest Fuel Reduction Operation in Southwest Oregon

Abstract

Most mechanical forest fuel reduction treatments prescribed to extract biomass are performed with existing or modified conventional logging equipment. Treatments that commonly harvest small, non-merchantable trees are often combined with or integrated into commercial thinning operations. Only a limited amount of literature has quantified harvesting system feasibility or environmental effects from such operations. The extra stand travel required to fell and extract small trees may lead to additional soil disturbance. The objective of this study was to assess soil disturbance from an integrated forest harvesting/mechanical forest fuel reduction operation in southwest Oregon, USA. The study was conducted in a fuel reduction thinning of a densely stocked 8.1-hectare (20-acre) mixed conifer stand on gentle terrain. A tracked, swing-boom feller-buncher and two rubber-tired, grapple skidders were used for felling and extracting both non-merchantable and merchantable trees. Visually classified soil disturbance, along with penetration resistance estimates were recorded pre- and post harvesting. Results indicate that the operation did not contribute to either statistically or biologically significant soil disturbance effects, based on an a priori biological reference threshold of 3,000 kPa. A history of multiple harvest entries, low soil moisture, and high initial soil strength conditions contributed to the lack of significant effects. This investigation will aid forest managers in decision making concerning expected soil disturbance effects when prescribing integrated harvesting systems for forest fuel reduction treatments.