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Tree-ring analysis of the fungal disease Swiss needle cast in the Western Oregon coast
Citation:
Lee, E., P. Beedlow, Ron Waschmann, C. Burdick, AND D. Shaw. Tree-ring analysis of the fungal disease Swiss needle cast in the Western Oregon coast. Presented at Swiss Needle Cast Cooperative Annual Meeting, November 29, 2012.
Impact/Purpose:
Swiss needle cast disease is specific to Douglas-fir (Pseudotsuga menziesii) and is endemic to the Pacific Northwest. The disease is caused by the fungus Phaeocryptopus gaeumannii and has been found to occur primarily in sites where mild winters and wet summers favor the pathogen’s growth and reproduction. Very little is known about the historic impacts of P. gaeumannii on Douglas-fir and whether the current Swiss needle cast epidemic in the PNW is due to environmental factors or was enhanced by the introduction of Christmas tree plantations in the mid 1970s or the planting of susceptible stock brought from outside the epidemic region. WED scientists have developed a statistical model using tree-ring width data to reconstruct the history of SNC disturbance on forest growth in coastal Oregon and examine the climatic factors that account for SNC impacts on Douglas-fir and their interactions with geography. The dendritic study indicates the disease dated as far back as 1590 and the impact of SNC on coastal Douglas-fir peaked in 1984-1986, followed by a decline to historic levels. Disease impact was associated with warm winters and warm, wet summers in humid areas where constant needle wetness is maintained by coastal fog and drizzle in summer and with warm winters and cool, wet summers in less humid areas. Disease impacts are expected to decrease in intensity but spread inland, north and to higher elevations in the Coast Range under a projected climate change scenario of warmer, drier summers. Our work is important for filling in the gaps of knowledge in understanding the disease effects on conifer forests in the Pacific Northwest under climate change scenarios and establishing a database of tree-ring and meteorological data across spatial scales.
Description:
Swiss needle cast (SNC) disease is specific to Douglas-fir (Pseudotsuga menziesii) and is native to the Pacific Northwest. The SNC disease is caused by the fungus Phaeocryptopus gaeumannii and has been found to occur primarily in sites where mild winters and wet summers favor the pathogen’s growth and reproduction. The goal of this study was to reconstruct the history of the disease and determine the climatic conditions that influence the disease and its impact on radial growth of Douglas-fir in western Oregon. Tree-ring data from six late-successional Douglas-fir stands in the western Oregon Coast Range were used to quantify the growth suppression and release patterns associated with the disease and to assess the climate-radial growth relationships. Cross-correlation and canonical correlation, spectral and time-series intervention analyses were performed using indexed annual ring width, and mean monthly precipitation and temperature data. Growth suppression patterns associated with Swiss needle cast disease were consistent across the six sites, indicating that the fungal disease and its impacts on radial growth of Douglas-fir were largely influenced by climatic conditions. At each site, reductions in radial stem growth (i.e., impact) due to the disease displayed periodicities associated with the maturation cycle of the fungus and climate. Growth suppression due likely to SNC was significantly correlated with current and previous winter and summer temperatures and summer precipitation up to a lag of 25 years. The disease dated back to the 1590s, which was the earliest record in our dendritic data. The impact of SNC on coastal Douglas-fir peaked in 1984-1986 at all six study sites, followed by unprecedented disease impacts of 100% in 1996 and 2004 at one humid, cool site or decreased to past historic levels at the other five less humid sites. Disease impact at the most infected site correlated best with winter and summer temperatures associated wi