The effect of spacing on Sitka spruce weevil damage to Sitka spruce

Abstract

Tree diameter, height, form, and number of stem defects were recorded in 26-year-old plantations of Sitka spruce, Piceasitchensis (Bong.) Carr., established at three initial spacings (2.74 × 2.74, 3.66 × 3.66, and 4.57 × 4.57 m). These plantations were heavily attacked by the Sitka spruce weevil, Pissodesstrobi Peck, from an early age. Denser plantations sustained a lower intensity of attack than the more open plantations. Although the three spacings had similar average number of stem defects per tree, trees in the close spacing had a significantly higher frequency of trees of good form relative to the more open plantations. It was concluded that trees planted at close spacing had lower levels of weevil damage. As a management regime, it is recommended that Sitka spruce plantations be started at close spacing (2.74 × 2.74 m) and precommercially thinned at age 25. By this age trees will average about 19 cm in dbh and 12 m in height, thus ensuring a first log of good quality.