Douglas-fir displays a range of growth responses to temperature, water, and Swiss needle cast in western Oregon, USA
Lee, EHenry, P. Beedlow, Ron Waschmann, D. Tingey, C. Wickham, S. Cline, Mike Bollman, AND C. McKinney. Douglas-fir displays a range of growth responses to temperature, water, and Swiss needle cast in western Oregon, USA. AGRICULTURAL AND FOREST METEOROLOGY. Elsevier Science Ltd, New York, NY, 221:176-188, (2016).
By the end of the 21st century, climate models predict hotter, drier summers and warmer, wetter winters in the Pacific Northwest (PNW), resulting in decreased snowpack, earlier snowmelt, and increased summer water balance deficit. These changes are already affecting sensitive forested ecosystems, raising concerns that forests are becoming increasingly susceptible to tree pathogens, phytophagous insects, and fires. Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) is a dominant PNW tree species that is infected by the foliar fungus Phaecryptopus gaeumannii (Rhode) Petrak which causes Swiss needle cast (SNC) disease. Very little is known about the interactive effects of climate and SNC on growth of Douglas-fir and the geographic extent of SNC impacts. WED scientists modeled Douglas-fir growth response to climate and SNC using tree-ring width data collected at nine mature forest stands in western Oregon, USA. WED scientists were first to show that: 1) SNC impacts occur wherever Douglas-fir is found and are not limited to the coastal fog zone as previously believed; 2) SNC impacts on Douglas-fir growth have been underreported and incorrectly attributed to temperature and water stress regionally; 3) dewpoint deficit and SNC affect growth interactively in that high evaporative demand during the annual summer drought reduces growth more in diseased years; 4) forest decline began ~1980 at dry sites in the Willamette Valley and ~1990 at mid-elevation Cascade sites in association with rising temperature; and 5) at drier sites, temperature and soil moisture affected growth interactively such that the temperature optimum for growth decreased with decreasing soil moisture. 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 PNW under climate change scenarios. As temperature rises and precipitation patterns shift towards wetter winters and drier summers, Douglas-fir will experience greater temperature and water stress and an increase in severity of SNC, resulting in decreased forest health and condition.
Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) growth in the Pacific Northwest is affected by climatic, edaphic factors and Swiss needle cast (SNC) disease. We examine Douglas-fir growth responses to temperature, dewpoint deficit (DPD), soil moisture, and SNC using time series intervention analysis of intra-annual tree-ring width data collected at nine forest stands in western Oregon, USA. The effects of temperature and SNC were similar in importance on tree growth at all sites. Previous-year DPD during the annual drought period was a key factor limiting growth regionally. Winter temperature was more important at high elevation cool sites, whereas summer temperature was more important at warm and dry sites. Growth rate increased with summer temperature to an optimum (Topt) then decreased at higher temperatures. At drier sites, temperature and water affected growth interactively such that Topt decreased with decreasing summer soil moisture. With climate change, growth rates increased at high elevation sites and declined at mid-elevation inland sites since ~1990. Growth response to climate is masked by SNC regionally. We conclude that as temperature rises and precipitation patterns shift towards wetter winters and drier summers, Douglas-fir will experience greater temperature and water stress and an increase in severity of SNC.