Fifty-year-old Sitka spruce plantations with a history of intense weevil attack

Abstract

The condition of 26 plantations of Sitka spruce (<i>Picea sitchensis</i> (Bong) Carr.) established between 1930 and 1935, at Green Timbers, Surrey, British Columbia, which sustained repeated attack by the white pine weevil (<i>Pissodes strobi</i> Peck) was examined in 1981. The plantations were started either as pure Sitka spruce or as a mixture of spruce and Douglas-fir (<i>Pseudotsuga menziesii</i> (Mirb.) Franco). A detailed survey was conducted in one plantation of each type for which annual infestation levels were recorded from 1936 to 1949 and which appeared to be typical of the rest of the pure and mixed plantations.

Many Sitka spruce trees were dead. having been out-competed by the other trees on the site as a result of repeated top-killing by <i>P. strobi</i>. Most surviving spruce trees were badly deformed, showed signs of severe attack, and were nonmerchantable. The plantation of pure Sitka spruce contained about 176 living Sitka spruce trees/ha, but only about 14 trees/ha were potential crop trees: the rest were suppressed or deformed. This plantation contained more volume in other volunteer conifers than in Sitka spruce. The mixed plantation developed into a merchantable stand of almost pure Douglas-fir, with only 5-6 Sitka spruce trees/ha.