Damage to Residual Trees and Advance Regeneration from Skyline and Forwarder Yarding in Mixed-Conifer Stands of Northeastern Oregon

Abstract

Abstract Reducing the risk of occurrence of wildfire and outbreaks of insects and diseases through fuel reduction is a priority management objective on federal lands within the Blue Mountains in northeastern Oregon. Optimal methods to achieve desired levels of fuel in mixed conifer stands by mechanical means are as yet unknown. One factor essential in evaluating optimal fuel reduction methods is the damage to residual trees and advance regeneration associated with specific combinations of stand condition, prescription, and harvesting system. Residual stem damage on 12,899 stems was compared after partial cutting and yarding with either skyline or ground-based forwarder in mixed conifer stands of northeastern Oregon. There were 6,092 occurrences of damage on 4,074 stems after yarding; 4.1% of the damaged stems had crushed foliage, 15.4% had a broken terminal leader, 26.5% had broken branches, 28.9% were wrenched, 35.0% had scraped bark, and 38.9% had bole scars. Fir (Abies grandis and A. lasiocarpa) seedlings were more frequently damaged than nonfir (Larix occidentalis, Picea engelmannii, and Pinus contorta) seedlings, and the most frequent damage to fir seedlings occurred in units treated by the forwarder. More damage occurred to residual large trees during yarding than to seedlings. Forwarder yarding resulted in slightly more damage to trees than did skyline yarding. Wrenching was generally consistent between residual seedlings and trees. Scarring occurred more frequently to residual trees than to seedlings. Mean scar area per tree on those actually scarred was generally about 40 cm² on seedlings and 256 cm² on residual trees. Despite slight differences in stand damage, both yarding methods met the silviculture prescription of reducing fuel and protecting large western latch, Engelmann spruce, Douglas-fir, and lodgepole pine stems targeted for retention. This suggests that the decision by resource managers to use one method of yarding over the other should probably be based on considerations such as availability of equipment, costs, and soil impacts. West. J. Appl. For. 15(2):101-107.