Indicators of conifer forest health in bark bettle-vectored fungal epidemics

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Worldwide, bark beetles and their fungal associates are devastating many forest ecosystems. Global warming increases the geographic range of bark beetles and affects the life cycle and survival of beetles and pathogens as well as tree physiological responses to pests. In Canada, outbreaks of mountain pine beetles (MPB) and spruce beetles are prime examples of major forest health risks impacting wood fibre supplies, biodiversity and forestry dependent communities. In British Columbia, MPB typically attacks mature lodgepole pine trees. Recent MPB attacks on different hosts and younger trees threaten new geographic areas, natural forest regeneration and planned reforestation. In this context, realistic assessments of large-scale forest health risks involve characterizing key factors in the dynamics of insect-vectored fungal epidemics, e.g. microbial diversity carried by the beetle, variability in fungal pathogenicity and fungal colonization of new hosts. Because very little information is available for such factors, we propose to a) assess traditional and new indicators of fungal pathogenicity on lodgepole pine using isolates of the most pathogenic fungal associate of MPB, b) determine whether MPB-fungal pathogens can colonize and be pathogenic to non-host trees (e.g. spruce), c) evaluate genetic markers that can differentiate virulent from non-virulent fungal isolates in an epidemic population, d) establish which tree defence mechanisms are activated and inactivated in host trees by virulent and non-virulent fungal pathogens, and e) establish which mechanisms allow fungal pathogens to overcome tree defences. To assess risks that the MPB epidemic could spread to other tree species and geographic regions, it is critical to address these issues and provide tools and information to government and forest products industries. The information will support decision-making in forest stewardship organizations aimed at preventing current and future epidemics from spreading to new regions and preparing for future bark beetle/fungal outbreaks. The active participation of the Canadian Forest Service as a supporting organization will allow for immediate transfer of new knowledge and tools from this project to the enduser.