What effects will a changing climate have on lodgepole pine in British Columbia?

The foliar compliment of evergreen conifer trees is dependent on the crown ratio and foliar longevity. Variation in foliage longevity is one of the important traits that often favours the genus Pinus over its competitors. Healthy lodgepole pine trees throughout British Columbia, Canada typically retain needles for 4 to 5 years. Foliar diseases have a profound influence on foliar longevity and crown ratio, and lodgepole pine is susceptible to a large suite of foliar pathogens. We assessed the foliar longevity, live crown percent and mortality of lodgepole pine trees at 25 lodgepole pine provenance test sites in central BC, and correlated these values with changes in climate at each site between the decade of the 1920s and the 1990s. We found strong relationships between increases in August minimum temperatures and live crown percent (R = -0.75) and mortality (R = 0.75). Sites in Region 7 of the trial (Robson Valley) consistently have the least foliage and have consistently experienced the greatest increases in August minimum temperature and July precipitation, and the greatest decreases in May maximum temperature. Region 9 (Nechako Plateau) sites consistently have the most foliage and have consistently experienced the least change in August minimum temperature, July precipitation, and greatest increases in May maximum temperature. Future changes in climate in conjunction with foliar pathogens could have profound effects on the health of lodgepole pine in BC. Introduction_________________ Climate change could influence plant disease by altering biological processes of the pathogen, host, or disease spreading organism (Harvell et al. 2002). In some instances, changes in precipitation regimes, though more difficult to predict than temperature (Barron 1995), could have the larger influence on forest productivity of the two climatic factors. Increases in summer precipitation could benefit some tree species (Nigh et al. 2004) but could also have unexpected impacts on tree growth if changes in moisture regime favours foliar pathogens (Woods et al. In: Jackson, M. B. comp. 2007. Proceedings of the 54th Annual Western International Forest Disease Work Conference; 2006 October 2—6; Smithers, BC. Missoula, MT: US Department of Agriculture, Forest Service, Forest Health Protection. Alex Woods is a Forest Pathologist with the BC Forest Service, Smithers, BC. Greg O'neill is a Forest Geneticist, BC Forest Service, Vernon BC. 2005). Foliar disease fungi may be some of the more responsive forest disease organisms to climate change (Woods et al. 2005). The foliar compliment of evergreen conifer trees is dependent on the crown ratio (Koch 1996), the ratio of crown length to total tree height, and foliar longevity. Longevity of foliage plays an important role in the overall life history of a tree (Schoettle and Fahey 1994). Variation in foliage longevity is one of the important traits that often favours the genus Pinus over its competitors (Schoettle and Fahey 1994). Foliar pathogens can have a profound influence on foliage longevity and therefore, on the competitive advantage of a species. Foliar diseases result in premature leaf mortality causing leaves to be shed prior to the end of their productive lives which leads to a loss of photosynthetic capacity and nutrients (Schoettle and Fahey 1994). Many foliar pathogens tend to attack needles in the lowest portions of tree crowns first, which often results in reduced crown ratios in infected trees. Lodgepole pine (Pinus contorta var. latifolia Dougl. ex Loud.) is host to a suite of foliar pathogens (Sinclair and Lyon 2005). These foliar diseases, under the influence of climate change, could potentially reduce any competitive advantage that a species like lodgepole pine may have had. Until recently, foliar diseases in natural forests have generally had a minor impact due to high levels of host resistance (Harrington and Wingfield 1998). Woods et al. (2005) have reported on a shift to this generalization occurring in northwest BC, where Dothistroma needle blight (Dothistroma septosporum Dorog. (Morlet)) is killing mature, native lodgepole pine, an unprecedented phenomenon they suggest is linked to climate change. Woods et al (2005) suggest that perhaps an environmental threshold for Dothistroma needle blight has been surpassed in northwest British Columbia allowing the foliar disease to overcome a previously established balance between host and pathogen. The objectives of this study were to: (1) determine what if any significant changes in climatic variables