The cooperative forestry research unit Commercial Thinning Research Network--9-year results

The Commercial Thinning Research Network (CTRN) was established throughout the spruce-fir forest of Maine beginning in 2000 with substantial funding from the University of Maine's Cooperative Forestry Research Unit. One of six replicates of the precommercially thinned stand condition in the CTRN is located in compartment 23A in the U.S. Department of Agriculture, Forest Service's long-term silviculture experiment on the Penobscot Experimental Forest (PEF), in which the experimental treatments are the timing of the first thinning entry and relative-density reduction. This paper presents 9-year results of this study, including detailed stand trajectories for the plots in compartment 23A. Contrary to expectations, there was no difference in periodic annual volume increment among the early-thinning treatments, owing to a much greater-than-expected growth response from the heavily thinned (50 percent reduction) plots. The study has provided valuable calibration data for the Forest Vegetation Simulator, and has informed landowner thinning decisions for a large area of northern Maine that was regenerated in the 1970s and 1980s during the spruce budworm salvage era. The study is actively maintained and future publications will document the effects of the 10-year delayed treatments.