Remeasurement data over a period of 35 years from fourteen 0.2023-ha permanent plots were analysed to determine the growth and yield effects of commercially thinning 50-year-old Douglas-fir stands on a good site on Vancouver Island, British Columbia. Compared to unthinned stands, the commercially thinned stands had:
- virtually the same total volume gross annual growth, top height, and top height growth;
- 12% more potentially usable total volume yield (including thinnings);
- 18% less total volume at final harvest age 86;
- virtually the same crop-tree (193 largest-diameter trees per hectare) average diameter, but 24% larger entire-stand quadratic mean diameter; and
- 11% less total volume production lost to mortality.
These results show that commercial thinning slightly increased total stand yield (including thinnings) and produced larger diameter trees at rotation age 86, but that it also reduced usable total volume at final harvest and had virtually no effect on size of the crop-trees. Data from this study are useful for validating growth models, and for constructing and comparing managed stand yield tables for various commercial thinning regimes.
FRDA Research Report 021 (372 KB)
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Updated July 24, 2015