Thinning experiment in Douglas-fir (EP 469)

Introduction

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 and represent a range of final densities. 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. In this case, thinning generally takes place 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.

Objectives

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

Treatments

The experiment was established in 1955 in a 17-year-old Douglas fir plantation (1.8m x 1.8m spacing) at Elk Falls Look-out near Campbell River. There are sixteen unreplicated plots in four series, with each plot within a series having a different thinning schedule. The plots vary in size from 0.091 ha to 0.303 ha. This experiment was established on a poor site and planned thinning was delayed due to poor response. Considerable snow damage occurred in 1968/69, which resulted in an unintentional reduction in the number of trees. Plans for further thinning were abandoned.

Status

Final measurement taken in 1994, released in 2001.