Biologists studying a lethal blight of lodgepole pines in northwestern British Columbia present strong evidence in the September issue of BioScience that climate change is to blame for the outbreak. The blight, caused by the fungus Dothistroma septosporum, causes trees to lose their needles and, in the case of the British Columbia outbreak, eventually die. D. septosporum has long been recognized as a pathogen of pines, but although it is considered a serious disease of exotic plantations in the Southern Hemisphere, it has until now been considered a minor threat to northern temperate forests. Lodgepole pines are an economically important species, being used in construction and for pulp.
Alex Woods and his colleagues at the British Columbia Forest Service and the University of Alberta investigated climate records in the area of the outbreak. The records provided no evidence of warming in the affected area in recent years, but they did reveal a clear increase in summer precipitation over the past decade. That constituted a smoking gun, because D. septosporum's life cycle depends on summer moisture for spore distribution. The increase in precipitation had no clear link to a known climatic oscillation that might have explained it, and the authors conclude that it is most likely related to a directional climate trend. The report of Woods et al. appears to represent one of a growing number of examples of an indirect effect of climate change, because increased summer precipitation would have been expected, absent D. septosporum, to benefit lodgepole pines.