Citation:

Lee, EHenry, P. Beedlow, Ron Waschmann, S. Cline, Mike Bollman, C. Wickham, R. Alfaro, AND N. Testa. Can a fake fir tell the truth about Swiss needle cast? 2015 Annual Meeting of the Swiss Needle Cast Cooperative, Corvallis, OR, December 01, 2015.

Impact/Purpose:

Forested watersheds and water quality in the west are highly vulnerable to rising temperatures and decreasing snowpack, making them more susceptible to forest pathogens, pests, and fires. Forests in the Pacific Northwest (PNW) are dominated by Douglas-fir (Pseudotsuga menziesii) and are host to many tree diseases (e.g., Swiss needle cast, laminated root rot, Armillaria root disease, and Schweinitzii butt rot) and phytophagous pests (e.g., Douglas-fir beetle, tussock moth, western spruce budworm). A key forest health concern in the Pacific Northwest (PNW) is the recent increase in severity, frequency and range of Swiss needle cast (SNC), a disease of Douglas-fir (Pseudotsuga menziesii) caused by the fungus, Phaeocryptopus gaeumannii. The causal fungus is endemic to the PNW but very little is known about its history and spatial extent of impact on growth of Douglas-fir and the epidemiology of SNC in relation to climate. A key question in dendroecology to reconstruct forest disturbance history is how to separate the confounding effects of climate, SNC and other forest disturbance agents. WED scientists have developed a statistical tool to identify the unique SNC disease cycle within a tree-ringwidth time series of Douglas-fir and discriminate between SNC and other forest disturbances. WED scientists were first to show that: 1) SNC impacts date back to 65,000 radioactive years B.P. which is the earliest record of Douglas-fir in the PNW; and 2) Douglas-fir on Vancouver Island of British Columbia have a forest disturbance history of both SNC and western spruce budworm. Our work indicates that the magnitude and range of SNC impacts on Douglas-fir growth in the PNW have been under-reported and were masked by climate and other forest disturbance agents. Our work is important for filling in the gaps of knowledge in understanding the complex interactions of temperature, water, and multiple biotic disturbance agents, in particular SNC, on conifer forests in the PNW under climate change scenarios. The regional impacts of SNC and other forest disturbances will likely increase under a changing climate, reduce tree growth and survivability, and ultimately change the composition, structure, and biogeography of some forest ecosystems.

Description:

A key question in dendrochronology to reconstruct forest disturbance history is how to distinguish between the effects of Swiss needle cast (SNC) and other forest disturbance agents (e.g., Douglas-fir beetle, tussock moth, western spruce budworm, laminated root rot, Armillaria root disease, and Schweinitzii butt rot) on radial stem growth of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). SNC impacts physiological processes of carbon and water relations by stomatal occlusion and early needle abscission resulting in a reduction of tree growth with a distinct periodicity, whereas phytophagous pests reduce tree growth by defoliation with epidemics following less regular pseudo-periodicities. Outbreaks of the various forest disturbance agents differ in their magnitude, frequency, and duration. In particular, SNC impacts on Douglas-fir growth display a primary periodicity of 6-30 years and a secondary periodicity of 3-5 years which is unique to the causal fungus Phaeocryptopus gaeumannii (Rhode) Petrak. We use frequency domain analysis of tree-ring chronologies of Douglas-fir to identify the SNC disease cycle and separate the confounding effects of climate, SNC, and other forest disturbances. We demonstrate the dendroecological reconstruction of SNC impacts on ancient Douglas-fir trees dated ~65K radioactive years B.P. from Eddyville, OR that were unearthed by the Oregon Department of Transportation. We demonstrate the dendroecological reconstruction of western spruce budworm (WSB) and SNC impacts on several contemporary, mature Douglas-fir stands on Vancouver Island of British Columbia where there were two known outbreaks of WSB around 1910 and 1929.

Record Details: