The white pine weevil, Pissodes strobi, is a serious pest of young white and Engelmann spruce, and their hybrid referred to as “interior spruce”. It also attacks Sitka spruce in coastal British Columbia as well as pine and spruce in eastern Canada and the United States. Weevil attack can reduce growth by as much as 40% in heavily attacked stands in high hazard zones. The most severe attacks occur in relatively open, fast growing stands that are 10 to 30 years old and between 2 and 20 m tall stands which may have received considerable forestry investment to encourage maximum growth. The weevil begins to attack spruce plantations when they are about five years old. Eggs are laid at the tip of the leader, just under the apical bud, in feeding punctures which are then covered with a fecal plug. After hatching, the larvae burrows downward consuming the phloem thereby destroying the tree’s apical shoot or leader. Although weevil attack does not kill trees, it reduces growth and deforms the stem. This reduces both tree volume and wood quality.
Mountain pine beetles, Dendroctonus ponderosae Hopkins (MPB) are a natural disturbance of North American pine forests, and outbreaks play an important role in directing ecological processes and maintaining the biological diversity of forest ecosystems. However, having infested about over 13 million hectares of lodgepole pine forests in British Columbia (BC) (Westfall & Ebata 2008) (Fig.1), the current beetle outbreak seems to be unprecedented in scale. As lodgepole pine comprises about one quarter of the provincial timber supply, socio-economic impacts of this beetle are enormous. A variety of management strategies can be used to reduce the effects of timber losses, the most important being salvage logging. In the short-term, adjusting harvest scheduling to remove standing beetle-killed trees can compensate some of the losses. However, due to market, operational, legal, and ecological constraints, the proportion of the beetle-killed forests that can be salvage-logged is limited.
Abstract Principal components analysis, followed by K‐means cluster analysis, was used to detect variations in the timing and magnitude of Pinus contorta Dougl. ex Loud. growth releases attributed to mountain pine beetle outbreaks in 31 stands of central British Columbia. Four major growth release patterns were identified from 1970 to 2000. Variations in the timing of growth releases among clustered stands corresponded well to aerial survey data indicating the timing of beetle outbreaks in the study area. Redundancy analysis was used to determine how variations in the timing and magnitude of growth releases attributed to beetle outbreaks changed with variations in climate or stand conditions over the study area. The first RDA axis, which accounted for 39% of the variations in growth patterns among stands, was significantly ( P <0.05) correlated with gradients in the percentage of pine in stands killed by mountain pine beetle, summer aridity, variation in summer precipitation, distance from initial infestation site, average pine age, and maximum August temperatures. The second RDA axis explained 6% of the variations and was significantly correlated with gradients in the beetle climate suitability index, extreme cold month temperatures, and site index. Comparisons of growth release patterns with aerial survey data and redundancy analyses indicated that dendrochronological techniques are useful for identifying mountain pine beetle outbreaks in central British Columbia, particularly among stands that had a density high enough to produce a growth release signal. Provided future studies account for interannual weather fluctuations, identification of growth increases due to stand thinning caused by beetle outbreaks will be useful for reconstructing the history of beetle outbreaks over much longer time periods.
Research programs to date in British Columbia on the biology, damage and control of the white pine weevil, Pissodes strobi (Peck), a pest of spruce, Picea spp. and pine, Pinus spp., are reviewed. Significant progress has been made in the areas of genetic resistance, silvicultural and chemical control. An integrated pest management (IPM) system is formulated which combines silviculture-driven and resistance-driven tactics. The system relies on accurate hazard rating of plantation sites and requires continuous monitoring of attack levels and the forecasting of plantation productivity under various IPM tactics through the use of a decision support system. Research needs which would increase effectiveness of the IPM system are reviewed and organized in the context of the plantation productivity cycle. Key words: insect control, Pissodes strobi, IPM, genetic resistance, silvicultural control, chemical control, decision support system
The effects of six fertilization treatments on tree height and incidence of attack by the white pine weevil, Pissodes strobi (Peck), on interior spruce (a hybrid, Picea glauca (Moench) Voss × Picea engelmannii Parry ex Engelm.) were explored in a field study. In a corresponding laboratory study, changes in constitutive and traumatic resin canal defences in response to fertilization were measured. Incidence of weevil attack increased with fertilization intensity. This trend was explained by increased resources available for weevil feeding (adults and larvae) as a result of increased leader size and bark thickness, as well as by an observed weakening in the tree's constitutive resin canal defences. The ability of interior spruce to produce a traumatic resin response was not influenced by fertilization. Although incidence of weevil attack was greatest in trees from the most intense fertilization treatments, height losses due to weevil attack were not as great as height gains due to fertilization treatment. Therefore, we concluded that fertilization is a feasible option for increasing productivity of interior spruce plantations, particularly if other weevil control alternatives are implemented.
Abstract An outbreak of the two-year cycle budworm (Choristoneura biennis Freeman) has caused defoliation damage to interior spruce (Picea engelmannii Parry × P. glauca (Moench)) and subalpine fir (Abies lasiocarpa [Hook.] Nutt.) forests of north central British Columbia for more than 10 yr and was ongoing in 1999. A sample of 429 increment cores from spruce, subalpine fir, and lodgepole pine (Pinus contorta var. latifolia Engelm.) was collected in areas of chronic defoliation, and used in a dendro-ecological study. The objective was to develop accurately dated ring-width chronologies of each species and, by comparing growth rates of the budworm host tree species (spruce and fir) with those of the nonhost pine, to determine the past history of budworm outbreaks in the region. This history would help in estimation of the potential duration and severity of the current outbreak in the region.Four periods of decade-long reduced growth attributable to budworm defoliation were identified in the increment cores from both spruce and subalpine fir. These occurred in the mid-1890s to the early 1900s, the mid-1920s to the mid-1930s, the 1950s to the early 1960s, and the late 1980s to present (1999). Outbreaks recurred approximately every 32 yr. The reduced growth period, indicative of past outbreaks, consisted of a growth reduction phase lasting 7 to 11 yr in which rings generally exhibited a pattern of alternating wide and narrow rings (a “saw-tooth” pattern). This pattern was attributed to the biennial nature of the life cycle of this budworm, in which severe damage is caused every other year. The growth reduction phase was followed by a growth recovery phase lasting 3 to 5 yr in which ring-width gradually returned to pre-outbreak levels. Thus, the entire growth loss period could last from 10 to 16 yr and cause an average annual loss in radial increment from 16 to 21%. The 32 yr cycle of outbreak recurrence was attributed to changes in forest structure in which the forest evolves from a nonsusceptible to a susceptible state as the proportion of subalpine fir present in the upper canopy increases relative to the spruce component. A 2 yr cycle budworm outbreak will selectively remove the subalpine fir component returning the forest to a less susceptible state. It was concluded that the 2 yr cycle budworm is an important disturbance agent of northern British Columbia forests causing significant growth loss. FOR. SCI. 48(4):722–731.
Variation in tree height and numbers of attacks by the Sitka spruce weevil (= white pine weevil), Pissodes strohi (Peck), were studied among families of a resistant provenance of Picea sitchensis (Bong.) Carr. at two Vancouver Island sites. At Sayward, after 14 years, the number of trees attacked varied by family from 0 to 80%. A significant association was found between the percentage of trees attacked in a family and the mean height of the family. Tall families were generally attacked more. At Fair Harbour (a clonal test), only 12% of the trees from the resistant provenance have been attacked after seven years, with all but one of the attacks concentrated on one of the two families tested. A multigenic or multicomponent basis for resistance is proposed and discussed.
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