Forest Investment Account (FIA) - Forest Science Program
FIA Project Y071321

    Development and analysis of climate change and forest health databases and models for BC: western spruce budworm and Douglas-fir
Project lead: Swain, Harry
Author: Murdock, Trevor Q.
Imprint: Victoria, BC : University of Victoria, 2007
Subject: Forest Investment Account (FIA), Choristoneura occidentalis, British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
This project addresses the FSP Timber Growth and Value Program Theme 7.0 – Climate Change and Research Priority a – Forest health. The purpose of this project is to develop standard climate spatial databases and climate change projection databases, compatible with the scale of recently developed natural disturbance databases and data on host distribution from forest inventory records, and to use these data to develop and test methods to predict the impacts of climate change on forest pests, using the western spruce budworm – Douglas-fir system as a test case. Climate change is now explicitly recognized as a major issue facing British Columbia’s forests (MOFR 2006). Two current forest health issues have been directly linked to climate change; Dothistroma needle blight (Woods et al. 2005) and Mountain pine beetle outbreak on lodgepole pine. The size and severity of the present mountain pine beetle outbreak has been attributed to range expansion by the mountain pine beetle due to an increase in climatically favourable habitat, and an increasing amount of lodgepole pine of susceptible age because of a decrease in the amount of stand-replacing disturbances (Taylor et al. 2006). Preliminary modeling analyses have been done of climate change impacts on biogeoclimatic zones, trees species ranges and climatic parameters (Hamann and Wang 2006, Wang et al 2006, Spittlehouse 2006, All show the potential for rapid widespread changes in forest ecosystems within the next rotation. Though none of these forecasts look at forest pests directly, they indicate major stress for forests trees associated with significant change in environmental factors controlling forest pests. Assessing the future of BC’s forests under the forcing of climate change is a complex task because of the pest-host interactions involved in forest health, the uncertainty and scale of results from climate models and the lack of knowledge of climate requirements of both hosts and pests. This proposed project focuses on compiling and developing appropriate climate data and output from climate models for investigating the future of forest health and testing the data with a single host-pest system. The deliverables would be a tested and relatively standard methodology of analysis, a comprehensive updatable climate data base for forecasting forest health for wide range of possible climates, and specific map-based forecasts for a specific forest health case: the spruce bud worm (Choristineura occidentalis) and Douglas-fir (Pseudotsuga menziesii). Budworms (Choristineura spp) are widespread in the forests of western North America. Speciation has occurred in response to diverse habitats and climates. Western spruce budworm occurs mainly in the range of its principal host Douglas-fir in south central British Columbia (Figure 1a) although larvae will also feed on the foliage of true firs, spruces, western larch and lodgepole pine (BC Ministry of Forests 1999). Two-year cycle budworm (C. biennis) is found on spruce and subalpine fir in north-central B.C. and at higher elevations in southern interior B.C, black-headed budworm (C. gloverana) is found on western hemlock in wetter coastal forests, and eastern spruce budworm (C. fumifera) occurs on spruce in the Boreal White and Black Spruce zone in northeast B.C. This project will focus on developing databases and techniques with reference to western spruce budworm but it is anticipated these techniques may be adapted for other budworm species. Western spruce budworm (WSBW) has a long association with Douglas-fir in western North America. Using dendrochronological methods, Swetman and Lynch (1993) documented nine regional-scale western spruce budworm outbreaks over approximately a 300 period in New Mexico, at the southern extent of its range; Campbell et al. (2005) documented seven outbreaks over a 300 year period near Kamloops, near the northern extent of WSBW outbreak distribution. Approximately 2.8 million ha of the 4.5 million ha of Douglas fir leading stands in BC have been affected by western spruce budworm since forest insect surveys began in the early 1900s (CFS unpublished data) (Figure 1b and Figure 2a). Outbreak frequency is variable and has been highest in the Pemberton area where at least 4 outbreaks have occurred in the past 80 years. Western spruce budworm has a one-year life cycle in BC. Adult moths lay eggs on the undersides of needles in August, larvae hatch about ten days later and spin hibernaculae in which they overwinter; larvae emerge the following spring. Outbreaks are associated with stands where developmental temperatures result in the emergence of over-wintering larvae in synchrony with spring bud swell and flush (Shepherd 1985). Larvae penetrate swelling buds (which have the highest food quality) and where they are protected from environmental extremes and predation. Figure 1. a. Distribution of collections of western spruce budworm in permanent sample plots within the range of Douglas-fir leading stands in B.C. (1960-1996) and b. annual outbreak areas (1909-2005) (CFS unpublished data). Figure 2. a . Distribution of western spruce budworm (WSBW) outbreaks by years of attack (CFS unpublished data) and b. Distribution of WSBW outbreaks by elevation and latitude (1960-2005) Early emergents cannot establish in buds and late emergents are exposed to an extended period of high mortality after budflush, although mature larvae will feed on older foliage if buds and new needles are in short supply. Outbreaks may last from one to two years to many years in a particular stand. Collapse of outbreaks may be related to extreme high temperatures during (July) moth flight and oviposition (Thomson 1985); the over-wintering stage is cold-tolerant and extreme winter temperatures are not believed to be a factor limiting distribution. The structure, composition and density of stands influences both the dynamics of the insect as well as the resultant stand damage (Maclauchlan 2004). Larval feeding on foliage can result in reduced tree growth, stem defects such as top-kill, and tree mortality. While the budworm will attack all ages of trees, mortality is most commonly seen in immature and suppressed understory trees (BC Ministry of Forests 1999). Repeated years of severe defoliation have resulted in mortality as high as 29% of trees (Alfaro and Wegwitz 1988). Reduced growth rate, both radial and height, has been quantified in several studies and has often been substantial, ranging from an average reduction in 8% of potential tree volume in one outbreak to 17% in another (Alfaro et al. 1982); individual trees have sustained over 30% reductions in potential volume (Alfaro 1986). Historically, western spruce budworm outbreaks are restricted by elevation (Figure 2b), but this is not related to distribution of suitable host stands or limits on dispersal, but appears to be related to differential survival. Population trends are synchronous over broad geographic areas (Shepherd 1985). Both of these observations suggest a climatic influence on outbreak distribution, frequency, and duration.
Related projects:  FSP_Y082321
Contact: Murdock, Trevor, (250) 472-4681,


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Updated August 16, 2010 

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