This project was initiated to address entomologists' uncertainty about the success of partial cutting as a method to reduce bark beetle-caused tree mortality. Implementing partial cutting of forests over a geographic area could help mitigate the spruce beetle (Dendroctonus rufipennis) outbreaks, which have been anecdotally linked to the changing climate throughout western North America. Improving the odds for residual spruce survival would lead to healthier and livelier forests for the public to recreate in.
Rocky Mountain Research Station scientists, partnered with Forest Service Forest Health Protection, initiated a project in Engelmann spruce (Picea engelmannii) stands on national forests in Arizona, Utah, and Wyoming. They sampled stands treated by various partial thinning methods and adjacent, non-treated stands for tree mortality. This study, published in Western Journal of Applied Forestry, is the first to show the effectiveness of partial cutting to reduce losses to spruce beetle.
Findings showed that partial forest cutting can, under typical bark beetle conditions, reduce tree mortality caused by spruce beetles. Among all surveyed forest stands, thinned stands had 7% mortality compared to 14% for unthinned stands. Untreated stands, however, had more residual spruce stems and basal area than treated stands. Most of this difference was among stems 3-11 inches in diameter, with little difference in survivorship among larger stems. Spruce regeneration was not significantly different among treated and untreated stands