Since 1989, three long-term experiments have been established in the British Columbia interior to determine the effects of precommercial thinning (spacing) on the future growth and yield of interior Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) stands under a variety of age, site, and stand conditions. This report provides a brief summary and overview of the results observed to date, and is intended to acquaint forest managers in the interior with the nature and progress of the trials. Thinning improved individual-tree growth, particularly diameter growth, with the greatest response occurring at the widest spacing. Thinning generally reduced basal area and total volume per hectare, and increased merchantable volume per hectare. The observation periods vary from 10 to 15 years, depending upon the experiment.
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Updated May 11, 2007