Soil disturbance and stream-adjacent disturbance from tethered logging in Oregon and Washington

摘要

Over the past century, the primary method for harvesting trees on steep slopes in the Pacific Northwest (PNW) was felling with chainsaws and yarding with cable systems, such as towers. Concerns over safety and higher logging costs on steep slopes have caused a shift in felling and/or yarding to ground-based machines tethered to an anchor, generally at the top of the slope. With the recent shift to tethered operations, there has been growing interest in the potential impact of machinery on steep slopes on streams and site productivity. We compared soil disturbance and stream-adjacent disturbance of tethered logging and conventional cable harvest methods on steep slopes in Oregon and Washington, USA. We sampled 30 harvest units that included either conventional (n = 15) or combination units with tethered (n = 15) harvesting systems to examine soil disturbance within a harvest unit and along stream channels. We compared potential impacts to stream adjacent-disturbance, erosion, and site productivity both between harvesting types within a harvest unit and between conventional versus combination units with tethered operations. We found that combination units with tethered operations had more stream-adjacent disturbance and soil disturbance than conventional cable-harvesting systems, but overall effects were below applicable regulatory thresholds for stream-adjacent disturbance and soil disturbance. Further, at the entire harvest-unit and within-unit scale, tethered operations had similar amounts of soil disturbance as mechanized harvesting systems. We did not find evidence of strong relationships between stream-adjacent disturbance or soil disturbance with either slope or soil depth. Across a wide variation of local site conditions in the PNW, tethered harvesting operations did not have extensive negative impacts on either soil disturbance or stream-adjacent disturbance, but further research could contribute to evolving best management practices and aligning forest practice regulations with current technologies.