Levels-of- Growing –Stock (LOGS) (EP 1256)
During the 1950s George Staebler, a research with Pacific Northwest (PNW) Research Station developed a scheme for estimating potential yields of thinned stands. This was based on the two concepts that (1) increment of thinned stands was little affected by stocking over a wide range of stocking, and (2) that gross yield of “normal” stands represented production potential of the site and would be little different from that of thinned stands. This work provided the first estimates of managed stand yields based specifically on PNW data. An associated concept was that within wide limits of stocking, growth percent should be inversely related to stocking. However, Staebler also recognized that his procedure and the inferred effect of stocking on growth percent depended on the assumption of constant gross volume increment over a wide range of stocking, which had never been tested for Douglas-fir. And, that there was very little data then available that could be used to test these assumptions or his numerical yield estimates. These questions, together with the general lack of thinned young stand data suitable for estimation of thinning effects, led to the Levels-of- Growing -Stock (LOGS) experimental design. A cooperative research program was undertaken between Oregon State University, PNW Research Station, Weyerhaueser, Washington Department of Natural Resources, and Canadian Forest Service.
Nine installations were established between 1963-1973 from Oregon to Vancouver Island. Specifications for each installation included:
- A relatively large (ca 9+ acres, ca 4+ ha) area of uniform site and stand, predominantly Douglas-fir, with initial stand height (original specification)* in the range 20-40 feet (6-12 m) and minimal crown recession. Both natural and plantation origin stands included.
- A completely randomized design with 8 thinning treatments plus control, replicated 3 times for a total of 27 plots.
- 1/5-acre (0.08 ha) plots meeting highly restrictive uniformity and comparability specifications.
- An initial “calibration” thinning to reduce all plots to comparable initial conditions. 16 crop trees per 1/5-acre plot were designated.
- 5 subsequent thinnings, made at intervals of 10 feet (3.03 m) of height growth, for a total of 60 feet (18.3 m) of growth after establishment. Cut trees to approximate the average diameter of non-crop trees (other than the selected 16 per plot).
- Residual stocking after each thinning defined as basal area after the previous thinning plus a specified percentage of the gross basal area periodic growth on the control.
- Four thinning treatments that retained fixed percentages of control plot gross basal area growth, two that retained an increasing percentage, and two that retained a declining percentage.
There were 2 installations established in B.C. by the Canadian Forest Service and are now managed cooperatively with BC Ministry of Forests, Lands, Natural Resource Operations and Rural Development.
To determine how the amount of growing stock retained in repeatedly thinned stands of Douglas-fir affects cumulative volume production, tree size development, and growth/growing stock ratios.
The two B.C. installations are located on Vancouver Island in the Sayward Forest near Campbell River on central Vancouver Island and near Shawnigan Lake on southern Vancouver Island. The Sayward Forest installation on northern Vancouver Island was established in the autumn of 1969 in a 22-year-old Douglas-fir stand planted in the spring of 1950 with 2-0 seedlings. The second study area at Shawnigan Lake was established during the winter of 1970/71 in a 25-year-old Douglas-fir stand planted in the spring of 1948 with 2-0 seedlings.
The eight thinning treatments applied were:
- Repeated heavy thinning
- Heavy to medium thinning
- Repeated medium-heavy thinning
- Medium-heavy thinning
- Repeated medium thinning
- Medium to heavy thinning
- Repeated light thinning
- Light to medium-heavy thinning
- Filipescu, C.N., E.C. Lowell, R. Koppenaal, and A.K. Mitchell. 2014. Modeling regional and climatic variation of wood density and ring width in intensively managed Douglas-fir. Can. J. For. Res. 44:220–229.
- Curtis, R.O., D.D. Marshall, and J.F. Bell. 1997. LOGS: a pioneering example of silvicultural research in coastal Douglas-fir. J. For. 95(7):19–25.