Forest Investment Account (FIA) - Forest Science Program
FIA Project Y071173

    Endemic spruce beetle (Dendroctonus ruffipenns) occurrence in trees, windthrow and logging debris in central interior British Columbia
Project lead: Taylor, Stephen
Contributing Authors: Thandi, Gurp; Taylor, Steve W.; Safranyik, Les; Linton, D.A.; Carroll, Allan L.
Subject: Forest Investment Account (FIA), Dendroctonus Rufipennis, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
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of forest insect outbreaks began in 1960, about 2 million ha of forest were affected by the spruce beetle (Figure 2, unpublished CFS data).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up about 76% of the approximately 14 million ha of spruce forest in B.C. (BC Ministry of Forests 1995 and Figure 1, CFS unpublished data).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 in the SubBoreal Spruce and Engelmann Spruce-Subalpine Fir biogeo-climatic zones (Figs. 3B and 3C, CFS unpublished data).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 attacked. Thus it is widely believed that a windfall event is needed to trigger an outbreak. However, during warmer periods, spruce beetle may complete their life cycle in one-year (univoltine) allowing spruce beetle populations to expand rapidly (Werner and Holsten 1985; Hansen et al. 2001). A higher proportion of univoltine broods is thought to increase the risk of spruce beetle outbreaks (e.g., Safranyik et al. 1990, Hansen and Bentz 2003). Spruce trees may also be less resistant to spruce beetle during drought events. A univoltine life cycle and drought resulting from climate change has been implicated in a long running outbreak on the Kenai peninsula in Alaska (Berg 2000) and in the current infestation in the Yukon (Garbutt 2005). Stand level impact assessment. Following a spruce beetle outbreak in the Prince George area from 1962 - 1968, the CFS initiated a study of spruce beetle population development (Safranyik 1974). Beetle attacks in stumps, windthrow and standing trees were sampled along about 25 km of line transects in two approximately 1000 and 2000 ha study areas in the SBS mc subzone, approximately 60 km east of Hixon, BC every year between 1972-1980. We propose to reanalyze this dataset to examine inter-annual variation in spruce beetle population and attacks in relation to windthrow and climate in central interior B.C. Landscape level risk modeling. While a spruce beetle risk rating system has been developed for BC using the infestation indices of elevation, site quality, spruce composition and stand age (Safranyik and Shore 2005) it does not explicitly include climatic factors and has not been implemented on a provincial basis. Logistic regression has been widely used to develop spatially-explicit habitat selection models for a wide variety of animal species (e.g., Manly et al. 2002, Boyce et al 2002, Keating and Cherry 2004 ). Chi-square tests have also been used to test hypotheses about habitat preferences with categorical data (Dasgupta and Alldredge 2000). We propose to use logistic regression and related techniques to test hypotheses about spruce bark beetle habitat preferences and develop a provincial-scale spruce beetle habitat selection model as a means of rating the probability of outbreak occurrence. A changing climate. Average temperatures have increased throughout much of British Columbia in the 20th century, with the largest increases seen in northern BC (BCWLAP 2002). Future increases on the order of 1-4ēC per century are projected by various climate models (BCWLAP 2002). A warmer climate could potentially affect the life history of the spruce beetle: while currently the beetle exhibits a primarily semivoltine life cycle, increasing average temperatures could result in an increase in univoltine broods. A changing climate has potential not only to alter the life cycle of the spruce beetle, but also to change the distribution of climactically suitable habitat. Carroll et al. (2004) found that the range of mountain pine beetle has apparently increased in the past 30 years in concert with an increase in the area of pine forest with moderate and high climatic susceptibility index. We propose to implement a climate based voltinism model in B.C. (Hansen et al. 2001) in order to examine whether voltinism has been significantly associated with outbreak occurrence in BC, and to examine the potential effects of climate change on voltinism and outbreak risk.


Final report - part 1 (0.6Mb)
Final report - part 2 (0.5Mb)
Final report - part 3 (0.2Mb)
Final report - part 4 (16.9Mb)

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Updated August 16, 2010 

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