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Dothistroma needle blight is an economically important forest disease which causes serious defoliation of many coniferous trees, particularly pine when planted out of their native range. The fungus responsible for the disease, Dothistroma septospora (Dorog.) Morelet infects the needles, leading to necrotic lesions, needle death and reduced wood yield. Until recently, Dothistroma needle blight has been uncommon and of little concern in lodgepole pine stands in western North America. During the past decade, however, prevalence of the disease has increased especially in northwestern British Columbia where severe damaged to managed and natural stands of lodgepole pine has been reported. The current outbreak of Dothistroma needle blight is much larger than what has been observed in the recorded past and is thought to be due in part to weather patterns that have been more conducive to the spread of the fungus: mild summer temperatures and prolonged periods of high humidity or leaf surface water films. Changes in weather conditions towards more frequent events of warm rains could be the principal cause of the current disease event. However, there are no studies investigating the history of Dothistroma outbreaks and its relationship with pre-recorded climate. More numerous and longer reconstructions of past Dothistroma are clearly needed to improve our understanding of this disturbance agent. The purpose of this research is to compare the influence of climate on the extent and nature of past Dothistroma outbreaks to understand the spatial and temporal variations of the disease in forests of northwestern British Columbia. Trees from approximately 30 sites will be sampled in subzones of the Sub-boreal Spruce and Interior Cedar Hemlock Zones to obtain cores and discs for tree ring analyses. A dendrochronological signal of the outbreak will be developed and compared with climate reconstructions at each site. Comparisons of outbreak frequency and duration, and weather patterns will be made between sites.
Kathy Lewis, C. Welsh.
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