Whoa on the wobble! Stem sinuosity in juvenile Douglas-fir across levels of genetic gain, silvicultural treatments, site conditions, and climatic variables in the Pacific Northwest

Managed forests serve as a natural climate change solution through sequestration of C and long-term storage in harvested wood products, in addition to providing ecosystem services and wildlife habitat. Specifically, com-modity products such as dimensional lumber and building materials, utilized from high-quality, defect free trees, provide greatest economic return and long-term C reservoir. Stem sinuosity is a noted deformity in juvenile coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) and can result in loss of value and degraded economic end-product. While the causal mechanisms have been of interest for decades, relatively little is known regarding the influence of tree improvement, silviculture, and local growing conditions. A network of experimental plots (n = 132) across six installations in the Pacific Northwest (PNW) were assessed to determine the effects of tree spacing, vegetation control, genetic gain, soil, site, and climate variables on stem sinuosity 10 years since planting. Sinuosity presence was greatest in wild genetic sources and on sites with low soil C and A horizon thickness. Severity increased with stem size and declined with concomitant gains in stand density and local windspeed. Findings suggest that site-specific deployment of genetic resources and silvicultural treatments may enhance Douglas-fir stem form in the PNW.