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Relationship between canopy structure, microclimate, and Swiss needle cast severity among different ages of Douglas-fir forests
Lan, Y., D. Shaw, P. Beedlow, E Henry Lee, AND Ron Waschmann. Relationship between canopy structure, microclimate, and Swiss needle cast severity among different ages of Douglas-fir forests. U.S. Environmental Protection Agency, Washington, DC, 2017.
Forest disturbance regimes are beginning to show evidence of climate-mediated shifts associated with climate change, raising concerns that forested ecosystems are becoming increasingly susceptible to forest management, tree pathogens, phytophagous insects, and fires. Understanding the physiological effects of climate and the important disturbance agents on forested watersheds and ecosystem services is critical to predicting future trends in response to climate change. Disturbance regimes have economic and ecological consequences in the Coastal Pacific Northwest where there is a major foliage disease (Swiss needle cast) epidemic occurring. WED scientists in collaboration with the Forest Engineering, Resources & Management, College of Forestry, Oregon State University studied the role of canopy structure and microclimate on Swiss needle cast (SNC) severity in young and mature Douglas-fir stands in western Oregon. A key finding is that SNC varies spatially but young Douglas-fir are more susceptible to SNC than mature trees everywhere the host species is found. SNC impacts were thought to be limited to Douglas-fir forests within the coastal fog zone, but our findings indicate that SNC is present at damaging levels inland. Our findings indicate that SNC is ubiquitous in Douglas-fir forests in the CPNW and is increasing in severity in habitats that were previously unsuitable for fungal development due to climate change. Our work is important for filling in the gaps of knowledge in understanding the complex interactions of temperature, water, and biotic disturbance agents on conifer forests in the CPNW under climate change scenarios. This report contributes to ACE CIVA 2.4.
Swiss needle cast (SNC) is an endemic disease of Douglas-fir caused by Phaeocryptopus gaeumannii. The fungus infects newly emerged needles between May and August. As the fungus develops, its fruiting bodies (pseudothecia) block the stomata and inhibit gas exchange, reducing the photosynthesis rate in infected trees. Based on observations, SNC is more severe in young trees than in mature trees. We hypothesize that the complexity in mature forests contributes to different microclimates, a factor for needle infection susceptibility. Mature forests have more structural diversity and micro-environments than young forests. We are currently examining the relationship between canopy structure, microclimate and SNC severity (percent of stomata occluded by pseudothecia) among different ages of Douglas-fir forests. The epidemiological research was conducted at five paired young and mature forest sites from the U.S. Environmental Protection Agency’s (EPA) Coast-to-Crest monitoring network beginning in 2015. At each site, three trees were selected and rigged for climbing to measure the severity of SNC in sampled needles from three canopy positions (lower, middle, and upper crown). SNC severity in relation to crown and branch morphology was examined by measuring the frequency and abundance of pseudothecia on individual needles by age class and canopy position as well as crown and branch structure. Leaf wetness sensors were installed in one study tree per site and used to record moisture on needle surface on lower, middle and upper canopy position. The preliminary results indicate that SNC severity varies by location and is greater in young Douglas-fir than mature trees at all sites.