Mid-Rotation Thinning Strategies in Lodgepole Pine Under Varying Stand Density Conditions: A TASS Simulation Study

Abstract

Stand density is a primary driver of structure, growth, and productivity in even-aged lodgepole pine (Pinus contorta var. latifolia) stands. This study evaluated responses across three mid-rotation lodgepole pine blocks using stand-level metrics and TASS growth modeling. Species-level analyses showed that lodgepole pine dominated all blocks, accounting for 74–95% of stand composition and exhibiting low variability across basal area, diameter, and stem density (CV ≤ 20%). In contrast, spruce, balsam fir, and deciduous species displayed high coefficients of variation (57–118%) which shows little contribution to stand structure or dynamics. Low Shannon diversity and evenness values further confirmed the monoculture nature of these stands. This supported the exclusion of minor species from growth modeling and the treatment of each block as a lodgepole pine monoculture in TASS simulations. When modeling thinning scenarios, the responses differed greatly depending on initial stocking level. In the overstocked block, thinning reduced early density driven mortality, increased diameter growth, and improved total volume by capturing stems otherwise lost to self-thinning. In the moderately stocked block, thinning increased individual tree size but reduced total yield. This showed that thinning timing is more critical than thinning intensity. In the understocked block, thinning provided minimal structural benefit and resulted in substantial volume loss. Results suggested that thinning is counterproductive when stands are below the Zone of Imminent Mortality (ZIM). Overall, results indicate that optimal management of lodgepole pine stands depends on maintaining mid-rotation stem densities near 900–1200 stems per hectare. This allows for the highest productivity by to minimizing mortality and maximize yield. Thinning is most beneficial in overstocked stands, due to competition induced mortality. Moderately stocked stands require delayed thinnings to fully take advantage of the treatment. While thinning is not recommended in understocked stands. This study emphasizes the importance of early density management and site-specific silvicultural prescriptions to optimize long-term stand productivity