Impacts on soils and residual trees from cut-to-length thinning operations in California's redwood forests

Abstract

Cut-to-length (CTL) harvest systems have recently been introduced for thinning third-growth, young (<25 years old) redwood forests (Sequoia sempervirens (Lamb. ex D. Don) Endl.) in northern California. This type of harvesting can effective for thinning overstocked stands consisting of small-diameter trees. However, forestland managers and government agencies overseeing forest operations have concerns about potential environmental impacts such as soil compaction or damage to remaining trees because harvesting often occurs when the soil is wet. This study was designed to (1) determine changes in soil physical properties (2) measure residual stand damage from a CTL thinning operation. Soil samples were collected from transects at two locations (track and center) on forwarder trails and reference (un-trafficked) points at three levels of soil depths (0-5, 10-15, and 20-25 cm). Stand damage was assessed as tree scaring was measured on all tree-sizes. We found significant differences between the wheel track and reference at the soil surface. There was no significant difference in the water infiltration rate between three locations because of high soil variability within small number of sample sizes, high moisture content, or high soil porosities. The way in which the scars occur depends on the composition of the redwoods. We measured larger sized-scars on remaining trees where trees were left in clumps as compared to individual trees, but the magnitude of damage was not different. Due to the few measureable effects on soil physical properties and residual tree damage, CTL thinning is viable during winter in this area.

Citation

Hwang, Kyungrok; Han, Han-sup; Marshall, Susan E.; Page-Dumroese, Deborah S. 2017. Impacts on soils and residual trees from cut-to-length thinning operations in California's redwood forests. In: Summary of Proceedings: 40th Council on Forest Engineering Annual Meeting; July 30-August 2, 2017; Hilton Garden Inn; Bangor, Maine. Online: http://cofe.org/pdfs/COFE_2017.pdf