The Douglas-fir thinning plots located at the Cowichan Lake Experiment Station, British Columbia were the first of their kind to be established in the Province in 1929 by S.R. Schenstrom. The original object was "to develop a yield table of several plots thinned by different methods to indicate the proper way of carrying out thinnings under different conditions" (Schenstrom 1931). Two methods of thinning and two intensities of each method were allocated to one plot each, and each compared to a single control plot. Although the original design called for crown and low thinnings, there has been no consistent application of treatments during the 50 years of the plots' existence. Competitors to potentially final crop trees were removed regardless of dominance in the classic interpretation of crown or low thinning methods.
In 1929, the stand was 18 years of age with approximately 7450 stems per hectare before thinning. After the initial carefully applied thinning in 1929, only dead and dying trees were removed during three ensuing thinnings in the next 15 years. Since 1947 more regular and heavy thinnings were made at approximately 3 year intervals until 1964. Then very light thinnings were made until 1978.
Despite the short comings of this pioneering experiment, it has provided some useful silvicultural experience.
It would seem sound practice to maintain levels of growing stock i.e. numbers of trees, by crown thinnings at a standard spacing of about 20% of the top height of the dominant trees. Furthermore, taking into account site differences, results indicate that whatever the intensity and method of thinning, including the unthinned control, there is no difference in gross volumes.
Finally a crown thinning over 12 hectares in the surrounding stand when 47 years of age, left trees of the same average diameter as those extracted. Ten years later the volume of wood removed during the thinning had been fully recovered.
Further details on the Schenstrom plots may be found in Research Note 1187 "Successive Thinnings in a Natural Stand of Douglas-fir over a Fifty Year Period" by G.C. Warrack, and can be obtained from ·tlle Information Branch, Ministry of Forests, Parliament Buildings, Victoria, British Columbia. V8W 3E7.
[Abstract contains full text of memo.]
BC Forest Service - Research Division. 1979. Successive thinnings in a natural stand of Douglas-fir over a fifty year period. British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development. Research Memo (FLNRORD). RM38
Topic: FLNRORD Research Program
Keywords: FLNRORD, Research Memo, British Columbia
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