A crop-tree thinning was conducted in a mid-slope, 31-year-old stand of Western larch (Larix occidentalis Nutt.) in the East Kootenays of British Columbia. Four radii of clearance were used; control, 2.4, 3.6 , 4.8 m. Initial tree sizes ranged from 2.5 to 15.0 cm DBH.
After 30 years the diameter, basal area, and volume growth response were proportional to the degree of spacing and the initial tree size. The response lasted for 25 years, but growth has declined dramatically in all treatments in the last 5 years. A number of potential causes of the decline are suggested.
The magnitude of this response is consistent with that found in other thinning studies in larch. The comparison shows that early thinning, before crown lift occurs, will maximize the growth response. At 31 years, this stand was too old for maximum response.
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Updated May 29, 2009