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.

Past infestations of the white pine weevil in naturally regenerated spruce stands

“…As expected (Alfaro and Omule 1990), weevil attacks in relation to height on the bole were more or less normally distributed in both subzones. The higher extent of attacks on the bole in the SBSvk than in the SBSwk could be explained by three hypotheses, among others.…”

“…It is also possible to reconstruct the retrospective stand epidemiology of the white pine weevil, Pissodes strobi (Peck), because most attacks leave a killed leader and a characteristic deformation in the bole of the tree (Alfaro 1989), both of which long remain visible on begins to attack susceptible spruce plantations as young as four to five years old; maximal attack intensities (numbers of trees attacked per year) occur in 10-30 year old stands. In plantations more than 30 years old, attack intensities gradually decline as the stand matures (Alfaro and Omule 1990). This decline may be caused by intraspecific competition between trees that reduces terminal leader size and thus food supply, by changes in leader microclimate, or by a decrease in susceptibility to the weevil (Alfaro 1994).…”

Role of genetic resistance in managing ecosystems susceptible to white pine weevil

“…Under these conditions, population explosions or outbreaks developed. Outbreaks on monocultured Sitka spruce (Alfaro and Omule 1990) Stand age 1). The rapid infestation increase in this initial stage is due to the large proportion of trees available for attack, and to the fact that many attacks result in multiple leaders, increasing the number of oviposition sites and the supply of food for the larvae.…”

Mortality of the white pine weevil associated with silvicultural practices in jack pine plantations

“…However, the literature shows contrasting results in terms of the influence of overstory shading and stand density on weevil populations. Although shaded stands tend to show lower levels of Infestation than exposed plantations in white pine (Stiell and Beny 1985;Wallace and Sullivan 1985), sitka spruce (Alfaro and Omule 1990), and white spruce (Picea glauca (Moench) Voss) (Taylor et al 1994), higher den-- sity of white pine weevils was found in seeded than in planted stands ofjack pine (Davidson 199 1) and attack rates have been independent of tree density in Norway spruce (Archambault et al 1993). Weevils killed a similar proportion of leaders in planted and seeded stands of jack pine (Table 1) (Bellocq and Smith 1994b).…”

“…Unfortunately, silvicultural prescriptions for pest control have been rarely used because little is known about their impact on the biology and ecology of the pest. Although some aspects of the biology of the white pine weevil and its relation with environmental factors or forestry practices were studied in white pine (Sullivan 196 I), sitka spruce (Alfaro and Omule 1990), and Norway spruce (Picea abies (L.) Karst.) (Archambault et al 1993) A synthesis of mortality factors which affect the white pine weevil in jack pine, based on a four-year study in northeastern Ontario is presented.…”