- Pekol, Joseph Robert
University of Maine School of Forest Resources
Pre-commercial (PCT) and commercial thinning (CT) are important silvicultural treatments in northern Maine, but their influence on stand growth and mortality have not been well quantified. In 2001, the University of Maine Cooperative Forestry Research Unit (CFRU) established the Commercial Thinning Research Network (CTRN) to measure the effects of PCT and CT on balsam fir (Abies balsemea) and red spruce (Picea rubens) stands throughout the state. Two experiments include repeated observations of individual trees over the last 10 years in 6 stands per experiment with 7 plots per stand, creating an extensive database. In this analysis, generalized linear mixed models (GLMM) were used to quantify the cumulative 10-year mortality as well as both the probability and rate of annual mortality due to the timing of (0, 5, and l0 years from plot establishment) and intensity of thinning (33 and 50% reduction in relative density) on young stands that have received PCT as well as method crown, low, and dominant thinning), and intensity of thinning on older stands without a history of PCT. In general, the PCT sites had lower cumulative mortality rates (0 - 32%) than the NoPCT sites (5 - 94%). Timing of CT and relative density (RD) reduction had no significant affect on PCT sites. When commercially thinning older, previously un thinned spruce stands, crown and dominant CT can significantly increase mortality compared to thinning from below Our results led us to recommend: (1) CT can be applied on a flexible time schedule to a PCT site, although. Waiting more than 25 years may lead to self-thinning; (2) waiting too long to CT a FCT site can increase the probability of mortality as the stand reaches a maximum RD; and (3) thinning from below can significantly reduce annual rates and occurrence of mortality, especially if PCT has not been applied.