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Endemic spruce beetle (Dendroctonus ruffipenns) occurrence in trees, windthrow and logging debris in central interior British Columbia
Thandi, Gurp
This project addresses two themes within the FSP Timber Growth and Value Program: ? Theme 4.0 ? Timber losses to environmental and biotic factors (wind, drought, insects, disease, animals, fire), Topic 4.2 ? Estimating stand-level losses (other than MPB), Research Priority a ? Spruce bark beetle. ? Theme 7.0 ? Climate Change, Research Priority a ? Forest health. The purpose of this project is to examine the relationship between climate, windthrow and spruce beetle populations and tree mortality at the stand level, and to develop landscape level models of spruce beetle occurrence risk based on host, climate and windthrow variables within the context of a changing climate. The spruce beetle (Dendroctonus rufipennis) is the most destructive pest of mature white and Engelmann spruce forests in British Columbia (Humphreys and Safranyik 1993). Since province-wide aerial overview surveys of forest insect outbreaks began in 1960, about 2 million ha of forest were affected by the spruce beetle (Figure 2, unpublished CFS data). Fig. 1. Age class distribution of spruce in B.C. ). Spruce beetles usually attack stands older than about 100 years, which make up about 76% of the approximately 14 million ha of spruce forest in B.C. (BC Ministry of Forests 1995 and Figure 1, CFS unpublished data). Thus the potential for significant spruce beetle outbreaks in the future is significant. Historically, spruce beetle outbreaks have affected pure spruce stands and mixed stands of spruce and subalpine fir and/or lodgepole pine Figure 2. Cumulative spruce bark beetle outbreaks in BC (1963-2004). Figure 3. Distribution of spruce bark beetle out-breaks in B.C during 1960 -2002 by severity class and (A) year (B) forest type (C) biogeoclimatic zone (D) latitude / elevation. in the SubBoreal Spruce and Engelmann Spruce-Subalpine Fir biogeo-climatic zones (Figs. 3B and 3C, CFS unpublished data). Mortality due to spruce beetle is variable; approximately 57, 27 and 16% of the area affected since 1960 was rated as low, moderate and severe (<10%, 10-30%, >30% mortality) respectively. Only a few studies of spruce beetle induced mortality have been carried out in BC. Safranyik (1985) used survey data from 29 stands located in the Willow and Bowron River drainages in central BC to examine relationships between tree diameter and spruce beetle-induced mortality, percent spruce mortality and stand density and mean diameter of spruce component, and effects of elevation, site quality, species composition, and stand age on the incidence of outbreaks of spruce beetle (Safranyik 1985). Infestation severities were divided into six groups based on percentage of spruce trees infested: 0-10%, 11-30%, 31-50%, 51-70%, and 71-100%. Regression analysis of the data set showed a linear relationship between diameter and percent spruce mortality in each of these groups. Trees under 8.84 cm DBH were not affected. The highest infestation index (observed infestations/ expected infestations) values were in stands over 100 years that better support brood development. About 5 spruce outbreak episodes were recorded in B.C. between 1963-2002 (Fig 3A). Using tree ring records, Zhang et al. (2001) also found evidence of canopy disturbance in spruce-subalpine fir forests in central B.C. during the 1720s and 1820s which they suggest may have been due to spruce beetle outbreaks. The episodic nature of spruce beetle outbreaks suggests a climatic link. There are a number of possible mechanisms whereby climate may influence spruce beetle populations that are related to spruce beetle life history and to host tree susceptibility. It generally takes two years for the spruce beetle to complete its (semi-voltine) life cycle in BC, although this can vary from 1-3 years (Safranyik et al. 1990). In the endemic state, spruce beetles exist in windfall, slash and other downed timber. However, when populations increase, often following windfall events, apparently healthy mature trees can be attacke ...
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Final report - part 1
Final report - part 2
Final report - part 3
Final report - part 4

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