A regional coastal Douglas-fir index of site quality for young stands in western Washington, USA

Abstract

Site index is frequently used for deciding how to manage stands, however, it often omits or fails to accurately characterize the site-dependent growth of young (ages ≤8 years) trees. This early stage of development is a critical period in a rotation during which important management decisions with the potential to influence all future growth are made. To address this, we developed a new index of site quality for young, coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) stands in western Washington, USA. We used high-density light detection and ranging (LiDAR) scans for 161 stands between 3 and 8 years old, in conjunction with Soil Survey Geographic Database information to identify site characteristics that were associated with productivity in young Douglas-fir sites. We utilized individual-tree detection algorithms to measure tree heights and developed a linear model for correcting LiDAR-derived heights in young Douglas-fir stands based on field-measured heights. Our findings indicated that Douglas-fir growth tended to be greatest on sites that were low in elevation, high in precipitation, and had fine-textured soils. We provide an index of site quality for young Douglas-fir based on elevation, precipitation, and soil textural classes to guide early stand management.

Citation

Boyle, Grady; Carter, David R.; Slesak, Robert; Thomas, Valerie; Strahm, Brian. 2025. A regional coastal Douglas-fir index of site quality for young stands in western Washington, USA. Forest Ecology and Management. 596: 123070. https://doi.org/10.1016/j.foreco.2025.123070.