Commercial Thinning Experiment : North Arm Forest (Cowichan Lake) - EP 364


This trial is the oldest commercial thinning experiment on the coast and was established by C. Joergensen of the B.C. Forest Service. By 1950, the 50 year old stand, originating from natural regeneration following clear felling in 1891, consisted of uniform, well-stocked Douglas-fir with a very minor component of western hemlock, western redcedar and grand fir. The thinnings were aimed at obtaining an evenly-distributed residual stand free from from poor quality trees. The study was originally intended to determine the utilization and profitability of thinning in immature Douglas-fir stands.


  1. To create a case-history of plots regularly commercially thinned for comparison with those not thinned. 
  2. To study the degree and composition of natural regeneration that follows thinning and clearfelling.


The experiment was established in 1950 near the North Arm of Cowichan Lake at the Cowichan Lake Research Station. Treatments consisted of 15 0.5 acre (.2027 ha) plots: 7 thinned, 7 unthinned and 1 clearfelled plot (to study regeneration). Thinning in 1951 removed as many of the poor quality trees as possible, leaving an even distribution of trees over the entire area of approximately; 174 trees/acre (430/ha) were removed leaving 221 stems/acrea (546/ha) standing with a basal area of 140 ft2/acre (32 m3). A second thinning 1970 (at age 70) reduced the volume back to 140 ft2/acre (32 m2/ha), 3 of the unthinned plots were clearfelled, and regeneration plots (0.0004 ha) were established within all 15 plots.