Correlated Curve Trend Study in Douglas-fir (EP 418)

Last updated on August 22, 2023


The Correlated Curve Trend experiment, was designed in South Africa and used throughout the world to evaluate the effects of different spacing and thinning strategies. The classical CCT experiment consists of 2 series of plots: a “spacing series” and a “thinning series”. Plots in the first series are spaced before the onset of competition down to  a range of final densities from 3000 to 125 stems per ha; once the target densities are achieved, the trees are left to grow without further thinning. The second series of plots is used to assess the impact of delayed thinning. These plots are established with various initial densities and are subsequently thinned at different rates and to varying degrees; generally after the onset of competition. Repeated measurement of the height and diameter of the trees are made for both series and the resulting growth curves are compared among plots (within and between series) to identify trends attributable to the effects of spacing and thinning. There were 3 Correlated Curve Trend experiments established on the B.C. coast: EP 418, 469 and 554.


To determine the influence and significance of growing space on the increment of trees and on the development of stands.


The experiment, established in 1952 near Cowichan Lake, consists of 17 plots. Plots 1 to 8 constitute the spacing plots, initially spaced to 3000sph and gradually thinned according to an interval to densities of 3000, 1500, 1000, 750, 500, 375, 250, 125 stems/ha respectively. Plots 9 to 17 constitute the thinning plots, representing different degrees of suppression and/or different degrees of release (thinning). The plots were rectangular (with most being square), their areas ranging from 0.091ha to 0.303ha, surrounded by a 15m wide buffers and a minimum distance between adjacent plots of at least 30m.


Last measured in 2003 before it was logged.