Thinning to meet sawlog objectives at shorter rotation in lodgepole pine stands

Abstract

We modelled how pre-commercial and commercial thinning affects development of merchantable timber, specifically large sawlogs (>20 cm diameter), on various site qualities and at different harvest ages. Data from juvenile permanent sample plots from post-harvest regenerated lodgepole pine stands in Alberta were projected using the Mixedwood Growth Model (MGM 21). Pre-commercial thinning (PCT) and different levels of commercial thinning (CT) with PCT were assessed on stands of good, medium, and fair site quality. Results show site quality alone had the greatest impact on merchantable yields with good sites producing ∼1.5 times the yield of medium and ∼4.3 times that of the fair sites. Moderate thinning on good sites produced a greater quantity of large sawlogs (>20 cm diameter) and their associated volume over unthinned stands than that on medium or fair sites, though thinning positively influenced total yield on these sites as well. On good sites, at age 50, CT treatments produced about ∼50 m3/ha more volume of large sawlogs (>20 cm) than the control; such gain drops to 18 m3/ha on medium sites. In addition, the mean annual increment culminated earlier on good sites, also enabling earlier harvest.