Pruning and Spacing of Douglas-fir (EP 1065.01)

Introduction

Pruning is often combined with pre-commercial thinning (also called juvenile spacing) in order to increase diameter growth of clear (knot-free) wood. The pruning of lower branches hastens the production of clear wood and ameliorates an undesirable effect of thinning, i.e., increased knot size due to prolonged branch retention. Pruning also accelerates other beneficial changes in bole growth related to the relative position of the live crown base. In 1991, a thinning and pruning experiment and a pruning severity trial were established in an 11 year-old coastal Douglas plantation near Chilliwack, B.C.

Objectives

  1. To compare the effects of 3 levels of pre-commercial thinning and 3 levels of pruning density (number of trees pruned) on the growth, yield and value of coastal Douglas-fir;
  2. To determine the effects of pruning severity on growth and survival of Douglas-fir. 

Treatments

The experiment was established in 1990 on Vedder Mountain near Chilliwack, B.C.

The thinning and pruning experiment included 3 levels of thinning (no thinning, thin to 500 and thin to 250 trees/ha) and 3 levels of pruning (no prune, prune 250 and prune all stems/ha) arranged in a 3x3 incomplete factorial. The 8 treatments were randomly assigned to sixteen 0.1 ha plots established in two separate blocks representing upper and lower slope positions. Thinning was uniform such that the average diameter ratio (d/D) of the trees removed (d) vs. that of the original stand (D) ranged from 0.96 to 1.00. Trees were pruned to a standard 3 m lift, or to 50% of tree height on trees less than 6 m tall. The prune 250 stems/ha treatment targeted those trees considered future crop trees. 

The pruning severity trial was established near the thinning and pruning experiment, using an unreplicated randomized design with four treatments (0, 1, 2 and 4 whorls remaining after pruning). The most severe pruning treatment removed all branches, retaining only stem foliage.

Status

Active.

Publications

  • de Montigny, L. and G. Nigh. 2014. Growth, mortality, and damage in fast growing Douglas-fir stands in coastal British Columbia twenty years after heavy juvenile thinning and moderate pruning at age nine. N.W. Sci. 88(3):206–218.
  • de Montigny, L. and S. Stearns-Smith. 2001. Thinning and pruning coastal Douglas-fir near Chilliwack, B.C.: 8-year results. B.C. Min. For., Res. Br., Victoria, B.C. Exten. Note 56.