Mapping Ixodes pacificus and Borrelia burgdorferi Habitat Suitability Under Current and Mid-Century Climate in the Pacific Northwest (BC and WA).

Introduction: Lyme disease is the most common vector-borne disease in the United States and Canada. The primary vector for the causative agent of Lyme disease, Borrelia burgdorferi, in the Pacific Northwest is the western blacklegged tick, Ixodes pacificus. Materials and Methods: Using active tick surveillance data from British Columbia, Canada, and Washington State, USA, habitat suitability models using MaxEnt (maximum entropy) were developed for I. pacificus to predict its current and mid-century geographic distributions. Passive surveillance data both from BC and WA were also visualized. Results: According to the constructed models, the number of frost-free days during the winter is the most relevant predictor of its habitat suitability, followed by summer climate moisture, ecoregion, and mean minimum fall temperature. The ensemble geographic distribution map predicts that the coastal regions and inland valleys of British Columbia and the Puget Lowlands of Washington State provide the most suitable habitats for I. pacificus. The density map of ticks submitted from passive surveillance data was overlaid on the current distribution map and demonstrates the correlation between numbers of submissions and habitat suitability. Mid-century projections, based on current climate change predictions, indicate a range expansion, especially of low and moderate suitability, from current distribution. Regarding Lyme disease risk, I. pacificus identified from both active and passive surveillance and tested positive for B. burgdorferi were found to be in areas of moderate to very high suitability for I. pacificus. Conclusion: According to developed models, the total suitable habitat area for I. pacificus will expand in the interior regions of British Columbia and Washington State. However, the risk remains small given relatively low infection rates among I. pacificus. Further studies are required to better understand how this might change in the future.

Heterogeneity in post-fire thermal responses across Pacific Northwest streams: A multi-site study.

Over the past century, water temperatures in many streams across the Pacific Northwest (PNW) have steadily risen, shrinking endangered salmonid habitats. The warming of PNW stream reaches can be further accelerated by wildfires burning forest stands that provide shade to streams. However, previous research on the effect of wildfires on stream water temperatures has focused on individual streams or burn events, limiting our understanding of the diversity in post-fire thermal responses across PNW streams. To bridge this knowledge gap, we assessed the impact of wildfires on daily summer water temperatures across 31 PNW stream sites, where 10-100% of their riparian area burned. To ensure robustness of our results, we employed multiple approaches to characterize and quantify fire effects on post-fire stream water temperature changes. Averaged across the 31 burned sites, wildfires corresponded to a 0.3 - 1°C increase in daily summer water temperatures over the subsequent three years. Nonetheless, post-fire summer thermal responses displayed extensive heterogeneity across burned sites where the likelihood and rate of a post-fire summer water temperature warming was higher for stream sites with greater proportion of their riparian area burned under high severity. Also, watershed features such as basin area, post-fire weather, bedrock permeability, pre-fire riparian forest cover, and winter snowpack depth were identified as strong predictors of the post-fire summer water temperature responses across burned sites. Our study offers a multi-site perspective on the effect of wildfires on summer stream temperatures in the PNW, providing insights that can inform freshwater management efforts beyond individual streams and basins.

A hybrid beachgrass (Ammophila arenaria × A. breviligulata) is more productive and outcompetes its non-native parent species.

The ability of non-native species to successfully invade new ecosystems sometimes involves evolutionary processes such as hybridization. Hybridization can produce individuals with superior traits that give them a competitive advantage over their parent species, allowing for rapid spread. Here we assess growth, functional morphology, and species interactions between two non-native beachgrass species (Ammophila arenaria and A. breviligulata) and their recently discovered hybrid (A. arenaria × A. breviligulata) on the U.S. Pacific Northwest coast. We asked whether the hybrid beachgrass differs from its parent species in morphology and growth, whether it competes with its parent species, and, if so, what are the potential mechanisms of competition. Plant taxa were grown in low- and high-density monocultures and in two-way interactions in a common garden environment. We show that the hybrid grew taller and more densely, with greater total biomass, than either parent species. The hybrid was also the better competitor, resulting in the model prediction of competitive exclusion against A. breviligulata and, depending on its relative abundance, A. arenaria. The hybrid displays a mixed 'guerilla-phalanx' growth form that allows it to spread laterally and achieve high shoot densities, giving it a competitive advantage. Given the current dominance of A. breviligulata compared to A. arenaria in most of the region where these taxa co-occur, we suggest that the hybrid will grow, compete, and spread quickly with potentially widespread consequences for the two non-native Ammophila congeners and the dunes they build.

DNA barcoding aids in generating a preliminary checklist of the lichens and allied fungi of Calvert Island, British Columbia: Results from the 2018 Hakai Terrestrial BioBlitz.

Background: Bioblitzes are a tool for the rapid appraisal of biodiversity and are particularly useful in remote and understudied regions and for understudied taxa. Lichens are an example of an often overlooked group, despite being widespread in virtually all terrestrial ecosystems and having many important ecological functions. New information: We report the lichens and allied fungi collected during the 2018 terrestrial bioblitz conducted on Calvert Island on the Central Coast of British Columbia, Canada. We identified 449 specimens belonging to 189 species in 85 genera, increasing the total number of species known from Calvert Island to 194, and generated Internal Transcribed Spacer (ITS) sequences for 215 specimens from 121 species. Bryoriafurcellata, Chaenothecopsislecanactidis and C.nigripunctata were collected for the first time in British Columbia. We also found Pseudocyphellariarainierensis, which is listed as Special Concern on the federal Species at Risk Act, and other rarely reported species in British Columbia including Opegraphasphaerophoricola, Protomicarealimosa, Raesaeneniahuuskonenii and Sareadifformis. We demonstrate that DNA barcoding improves the scope and accuracy of expert-led bioblitzes by facilitating the detection of cryptic species and allowing for consistent identification of chemically and morphologically overlapping taxa. Despite the spatial and temporal limitations of our study, the results highlight the value of intact forest ecosystems on the Central Coast of British Columbia for lichen biodiversity, education and conservation.

A pulse crop dataset of agronomic traits and multispectral images from multiple environments.

Crop yield potential in breeding trials can be captured using unmanned aerial vehicle (UAV) based multispectral imagery. Several digital traits or phenotypes such as vegetation indices can represent canopy crop vigor and overall plant health, which can be used to evaluate differences in performance across varieties in crop breeding programs. This dataset contains agronomic data for named cultivars and breeding lines of spring-sown dry pea and chickpea, and over 275 multispectral images from advanced and preliminary breeding trials. The breeding trials were located at three locations in the "Palouse" region of Eastern Washington and Northern Idaho of the United States across 2017, 2018 and 2019 cropping seasons. The multispectral images were captured using a UAV integrated with a 5-band multispectral camera at multiple time points from early vegetative growth through pod development stages during each cropping season. This dataset details seed yield information from trials of dry peas and chickpea that were obtained from each location, as well as additional agronomic and phenological data recorded at one location (mostly Pullman, WA) for each cropping season. The dataset also includes 20-78 megabytes (MB) Tagged Image Format (TIF) uncalibrated stitched orthomosaic images generated from the photogrammetric software. The images can be processed using any convenient image processing algorithm to obtain vegetation indices and other useful information.

Spatial and Temporal Variability in Stream Thermal Regime Drivers for Three River Networks During the Summer Growing Season.

Many cold-water dependent aquatic organisms are experiencing habitat and population declines from increasing water temperatures. Identifying mechanisms which drive local and regional stream thermal regimes facilitates restoration at ecologically relevant scales. Stream temperatures vary spatially and temporally both within and among river basins. We developed a modeling process to identify statistical relationships between drivers of stream temperature and covariates representing landscape, climate, and management-related processes. The modeling process was tested in 3 study areas of the Pacific Northwest USA during the growing season (May [start], August [warmest], September [end]). Across all months and study systems, covariates with the highest relative importance represented the physical landscape (elevation [1st], catchment area [3rd], main channel slope [5th]) and climate covariates (mean monthly air temperature [2nd] and discharge [4th]). Two management covariates (ground water use [6th] and riparian shade [7th]) also had high relative importance. Across the growing season (for all basins) local reach slope had high relative importance in May, but transitioned to a regional main channel slope covariate in August and September. This modeling process identified regionally similar and locally unique relationships among drivers of stream temperature. High relative importance of management-related covariates suggested potential restoration actions for each system.

Evaluating variations in the barriers to colorectal cancer screening associated with telehealth use in rural U.S. Pacific Northwest.

PURPOSE: The incidence and mortality rates of colorectal cancer (CRC) remain consistently high in rural populations. Telehealth can improve screening uptake by overcoming individual and environmental disadvantages in rural communities. The present study aimed to characterize varying barriers to CRC screening between rural individuals with and without experience in using telehealth. METHOD: The cross-sectional study surveyed 250 adults aged 45-75 residing in rural U.S. states of Alaska, Idaho, Oregon, and Washington from June to September 2022. The associations between CRC screening and four sets of individual and environmental factors specific to rural populations (i.e., demographic characteristics, accessibility, patient-provider factors, and psychological factors) were assessed among respondents with and without past telehealth adoption. RESULT: Respondents with past telehealth use were more likely to screen if they were married, had a better health status, had experienced discrimination in health care, and had perceived susceptibility, screening efficacy, and cancer fear, but less likely to screen when they worried about privacy or had feelings of embarrassment, pain, and discomfort. Among respondents without past telehealth use, the odds of CRC screening decreased with busy schedules, travel burden, discrimination in health care, and lower perceived needs. CONCLUSION: Rural individuals with and without previous telehealth experience face different barriers to CRC screening. The finding suggests the potential efficacy of telehealth in mitigating critical barriers to CRC screening associated with social, health care, and built environments of rural communities.

The Pacific Northwest Harmful Algal Blooms Bulletin.

A bulletin communicating risk of toxic Pseudo-nitzschia blooms to shellfish harvest along the open coast of the Pacific Northwest region of the United States (the northeast Pacific Ocean spanning Washington and Oregon) is discussed. This Pacific Northwest Harmful Algal Blooms (PNW HAB) Bulletin is designed for shellfish managers with a focus on the razor clam fishery, but may also be informative to managers of the Dungeness crab fishery since domoic acid accumulation in crabs tends to lag accumulation in razor clams by a couple of weeks. The Bulletin complements beach phytoplankton monitoring programs by alerting coastal shellfish managers about adverse environmental conditions that could be conducive to a toxic Pseudo-nitzschia bloom. Beach monitoring programs are effective at determining when toxins have arrived at shellfish beaches, but a risk forecast based on near real-time biophysical information can provide managers with additional forewarning about potential future toxin outbreaks. Here, the approaches taken in constructing the risk forecasts, along with the reasoning and research behind them are presented. Updates to a historical PNW HAB Bulletin are described, as are the current workflow and the individual components of the updated Bulletin. Some successes and failures realized throughout the process are also pointed out for the benefit of the broader community. A self-assessment suggests that when the necessary data sources are available, the PNW HAB Bulletin provides an accurate forecast of risk associated with toxic Pseudo-nitzschia blooms. The Bulletin has proven beneficial to coastal shellfish managers by better informing decisions on sample collection, and harvest limits, openings, extensions, and closures.

Insights from specimen data for two economic Chrysobothris species (Coleoptera: Buprestidae) in the western United States.

Chrysobothris mali Horn and Chrysobothris femorata (Olivier) (Coleoptera: Buprestidae) are wood-boring beetles native to western North America. Both species are highly polyphagous, feeding on a wide range of deciduous trees and shrubs, including fruit and nut trees as well as shade trees grown as nursery stock. Chrysobothris femorata is widely distributed across North America, while C. mali occurs west of the Rocky Mountains. There is a notable lack of basic biological information regarding both species' phenology and distributions in the Pacific Northwest. To better understand the biology of these economically important insects, seasonal adult collection information, host plant association data, and morphological measurements were collected from preserved specimens residing in 5 major regional arthropod collections. Label information was collected from 661 C. mali and 165 C. femorata specimens. Collection location data were used to create a map of C. femorata and C. mali distributions in the western United States, indicating that C. femorata is significantly less abundant in California, Oregon, and Washington than C. mali. Of the 50 associated plant taxa noted on specimen labels, only 4 associations were shared between the species, potentially indicating host specialization. New reproductive hosts are recorded for C. femorata (2 hosts) and C. mali (3 hosts). Tree species commonly damaged by flatheaded borers in commercial orchards and nurseries were not present in the historical records. The insights gleaned from specimen data allow researchers to better understand the biology and ecology of these understudied, yet economically impactful insects in the western United States.

Emergence of persistent institutionalized inequality at the Bridge River site, British Columbia: the roles of managerial mutualism and coercion.

Persistent institutionalized inequality (PII) emerged at the Bridge River site by ca 1200-1300 years ago. Research confirms that PII developed at a time of population packing associated with unstable fluctuations in a critical food resource (anadromous salmon) and persisted across multiple generations. While we understand the demographic and ecological conditions under which this history unfolded, we have yet to address details of the underlying social process. In this paper, we draw on Bridge River's Housepit 54 to examine two alternative hypotheses. Hypothesis 1, mutualism, suggests that household heads signalled to maintain and attract new members as a means of supporting the demographic viability of the house. Inequality is indicated by variation in prestige markers but less obviously in economic fundamentals. Hypothesis 2, coercion, asserts that the more successful households developed control over access to critical food resources, forcing others into the choice between emigration and subjugation. Inequality is indicated by inter-family differences in prestige markers and economic fundamentals. Results suggest that inequality emerged under a mutualism scenario but persisted for subsequent generations under more coercive conditions. This article is part of the theme issue 'Evolutionary ecology of inequality'.

Production and perception of prevelar merger: Two-dimensional comparisons using Pillai scores and confusion matrices.

Vowel merger production is quantified with gradient acoustic measures, while phonemic perception methods are often coarser, complicating comparisons within mergers in progress. This study implements a perception experiment in two-dimensional formant space (F1 × F2), allowing unified plotting, quantification, and statistics with production data. Production and perception are compared within 20 speakers for a two-part prevelar merger in progress in Pacific Northwest English, where mid-front /ɛ, e/ approximate or merge before voiced velar /É¡/ (leg-vague merger), and low-front prevelar /æÉ¡/ raises toward them (bag-raising). Distributions are visualized with kernel density plots and overlap quantified with Pillai scores and confusion matrices from linear discriminant analysis models. Results suggest that leg-vague merger is perceived as more complete than it is produced (in both the sample and community), while bag-raising is highly variable in production but rejected in perception. Relationships between production and perception varied by age, with raising and merger progressing across two generations in production but not perception, followed by younger adults perceiving leg-vague merger but not producing it and varying in (minimal) raising perception while varying in bag-raising in production. Thus, prevelar raising/merger may be progressing among some social groups but reversing in others.

A data set for pollinator diversity and their interactions with plants in the Pacific Northwest.

Pollinator populations have declined substantially in recent years. The resulting loss in pollination services has both ecological and economic consequences, including reductions in plant diversity and crop production and lower food security. Data sets that identify pollinators and their plant hosts are of the utmost importance for the light can shed on the main causes of pollinator declines. Here we present a data set that contains 67,954 individual pollinator records. The data were collected across the Pacific Northwest, primarily focused in British Columbia (Canada), with 182 individual sites over 11 years, between 2005 and 2017. This data set comprises multiple studies that aimed to collect information on pollinator abundance, diversity, and their interactions with plants. Overall, the data set includes 937 morphospecies (of which 482 were identified to the species level) of pollinators across 105 families, including data for bees, wasps, butterflies, moths, and flies. We also present information on the interactions of these species, with 473 species of plants. The data set is being released for noncommercial use only. Credits should be given to this paper (i.e., proper citation).

Economic impacts of harmful algal blooms on fishery-dependent communities.

The recreational razor clam fishery is the largest recreational bivalve fishery in the Pacific Northwest and a major source of tourism-related income to small communities in the region. Delays and closures of recreational shellfisheries due to the increasing frequency of harmful algal blooms (HABs) threaten to have significant negative impacts on fishery dependent communities. Coupling previous recreational shellfishing expenditure estimates from the literature with a novel dataset of daily visits to local businesses, we estimate a range of economic impacts resulting from the cancellation of razor clam digs at Long Beach, WA, the most popular beach in the State for recreational clam diggers. Our results indicate that a full season closure can lead to lost sales revenues of $16,875 for gas stations, $117,600 for food stores, $217,800 for accommodations and $491,400 for food service places for a total lower bound economic impact of $843,675. We discuss the opportunity for early warning systems, like the Pacific Northwest HAB Bulletin, to guide policy and facilitate business decisions that hedge the risk of revenue losses associated with dig cancellations.

Broad-scale eDNA sampling for describing aquatic species distributions in running waters: Pacific lamprey Entosphenus tridentatus in the upper Snake River, USA.

One of the most fundamental yet challenging tasks for aquatic ecologists is to precisely delineate the range of species, particularly those that are broadly distributed, require specialized sampling methods, and may be simultaneously declining and increasing in different portions of their range. An exemplar is the Pacific lamprey Entosphenus tridentatus, a jawless anadromous fish of conservation concern that is actively managed in many coastal basins in western North America. To efficiently determine its distribution across the accessible 56,168 km of the upper Snake River basin in the north-western United States, we first delimited potential habitat by using predictions from a species distribution model based on conventionally collected historical data and from the distribution of a potential surrogate, Chinook salmon Oncorhynchus tshawytscha, which yielded a potential habitat network of 10,615 km. Within this area, we conducted a two-stage environmental DNA survey involving 394 new samples and 187 archived samples collected by professional biologists and citizen scientists using a single, standardized method from 2015 to 2021. We estimated that Pacific lamprey occupied 1875 km of lotic habitat in this basin, of which 1444 km may have been influenced by recent translocation efforts. Pacific lamprey DNA was consistently present throughout most river main stems, although detections became weaker or less frequent in the largest and warmest downstream channels and near their headwater extent. Pacific lamprey were detected in nearly all stocked tributaries, but there was no evidence of indigenous populations in such habitats. There was evidence of post-stocking movement because detections were 1.8-36.0 km upstream from release sites. By crafting a model-driven spatial sampling template and executing an eDNA-based sampling campaign led by professionals and volunteers, supplemented by previously collected samples, we established a benchmark for understanding the current range of Pacific lamprey across a large portion of its range in the interior Columbia River basin. This approach could be tailored to refine range estimates for other wide-ranging aquatic species of conservation concern.

Using long-term citizen science data to distinguish zones of debris accumulation.

Studies show that a driver of coastal debris is the rate between debris deposition and resuspension; however, the influence of beach zone topography on the distribution of debris remains poorly understood. Using five years of marine debris data collected by the COASST citizen science program, we explored the spatiotemporal trends in debris abundance within two regions of the United States Pacific Northwest and investigated whether higher debris loads are associated with beach zones that have a higher propensity to trap debris. We found that beaches with larger wood zones had higher debris loads, adding to the growing evidence that backshore areas of beaches act as sinks for debris. Higher debris loads were also associated with beaches that had larger wrack zones suggesting that onshore transport from the marine reservoir is a dominant source of debris. This study provides a long-term baseline of marine debris which managers could use to inform source reduction interventions.

The streamwater microbiome encodes hydrologic data across scales.

Many fundamental questions in hydrology remain unanswered due to the limited information that can be extracted from existing data sources. Microbial communities constitute a novel type of environmental data, as they are comprised of many thousands of taxonomically and functionally diverse groups known to respond to both biotic and abiotic environmental factors. As such, these microscale communities reflect a range of macroscale conditions and characteristics, some of which also drive hydrologic regimes. Here, we assess the extent to which streamwater microbial communities (as characterized by 16S gene amplicon sequence abundance) encode information about catchment hydrology across scales. We analyzed 64 summer streamwater DNA samples collected from subcatchments within the Willamette, Deschutes, and John Day river basins in Oregon, USA, which range 0.03-29,000 km2 in area and 343-2334 mm/year of precipitation. We applied information theory to quantify the breadth and depth of information about common hydrologic metrics encoded within microbial taxa. Of the 256 microbial taxa that spanned all three watersheds, we found 9.6 % (24.5/256) of taxa, on average, shared information with a given hydrologic metric, with a median 15.6 % (range = 12.4-49.2 %) reduction in uncertainty of that metric based on knowledge of the microbial biogeography. All of the hydrologic metrics we assessed, including daily discharge at different time lags, mean monthly discharge, and seasonal high and low flow durations were encoded within the microbial community. Summer microbial taxa shared the most information with winter mean flows. Our study demonstrates quantifiable relationships between streamwater microbial taxa and hydrologic metrics at different scales, likely resulting from the integration of multiple overlapping drivers of each. Streamwater microbial communities are rich sources of information that may contribute fresh insight to unresolved hydrologic questions.

The role of multiple Pleistocene refugia in promoting diversification in the Pacific Northwest.

Pleistocene glacial cycles drastically changed the distributions of taxa endemic to temperate rainforests in the Pacific Northwest, with many experiencing reduced habitat suitability during glacial periods. In this study, we investigate whether glacial cycles promoted intraspecific divergence and whether subsequent range changes led to secondary contact and gene flow. For seven invertebrate species endemic to the PNW, we estimated species distribution models (SDMs) and projected them onto current and historical climate conditions to assess how habitat suitability changed during glacial cycles. Using single nucleotide polymorphism (SNP) data from these species, we assessed population genetic structure and used a machine-learning approach to compare models with and without gene flow between populations upon secondary contact after the last glacial maximum (LGM). Finally, we estimated divergence times and rates of gene flow between populations. SDMs suggest that there was less suitable habitat in the North Cascades and Northern Rocky Mountains during glacial compared to interglacial periods, resulting in reduced habitat suitability and increased habitat fragmentation during the LGM. Our genomic data identify population structure in all taxa, and support gene flow upon secondary contact in five of the seven taxa. Parameter estimates suggest that population divergences date to the later Pleistocene for most populations. Our results support a role of refugial dynamics in driving intraspecific divergence in the Cascades Range. In these invertebrates, population structure often does not correspond to current biogeographic or environmental barriers. Rather, population structure may reflect refugial lineages that have since expanded their ranges, often leading to secondary contact between once isolated lineages.

Genomic evidence of an ancient inland temperate rainforest in the Pacific Northwest of North America.

The disjunct temperate rainforests of the Pacific Northwest of North America (PNW) are characterized by late-successional dominant tree species Thuja plicata (western redcedar) and Tsuga heterophylla (western hemlock). The demographic histories of these species, along with the PNW rainforest ecosystem in its entirety, have been heavily impacted by geological and climatic changes the PNW has experienced over the last 5 million years, including mountain orogeny and repeated Pleistocene glaciations. These environmental events have ultimately shaped the history of these species, with inland populations potentially being extirpated during the Pleistocene glaciations. Here, we collect genomic data for both species across their ranges to test multiple demographic models, each reflecting a different phylogeographical hypothesis on how the ecosystem-dominating species may have responded to dramatic climatic change. Our results indicate that inland and coastal populations in both species diverged ~2.5 million years ago in the early Pleistocene and experienced decreases in population size during glacial cycles, with subsequent population expansion. Importantly, we found evidence for gene flow between coastal and inland populations during the mid-Holocene. It is likely that intermittent migration in these species during this time has prevented allopatric speciation via genetic drift alone. In conclusion, our results from combining genomic data and demographic inference procedures establish that populations of the ecosystem dominants Thuja plicata and Tsuga heterophylla persisted in refugia located in both the coastal and inland regions of the PNW throughout the Pleistocene, with populations expanding and contracting in response to glacial cycles with occasional gene flow.

A re-survey in 2019-2021 of winter bird communities in the Oregon Coast Range, USA, initially surveyed in 1968-1970.

Background: Long-term changes in bird populations during winter are poorly evaluated in many parts of the world. We re-surveyed forest bird communities during winter, 2019-2021, in seven large plots originally surveyed from 1968 through to 1970, near Corvallis, Oregon, USA by Stanley Anderson, a graduate student at Oregon State University in the 1960s. Anderson counted birds and measured forest plant communities within the forests dominated by Douglas-fir (Pseudotsugamenziesii) in the Coast Range Mountain foothills. His thesis included plot locations, summaries of vegetation characteristics and point estimates of bird densities for each plot. To our knowledge, the Anderson data represent the oldest structured survey of Pacific Northwest winter forest bird communities with density estimates. Given the paucity of similar data, we re-surveyed his plots after aligning methods with his and adding modern components (distance and time interval sampling) to facilitate comparisons of changes in abundances. We preserved more extensive metadata than were preserved from Anderson's surveys, including georeferenced point count survey locations to facilitate more precisely repeatable future re-surveys. New information: Original surveys of winter bird populations in the Pacific Northwest, USA, based on georeferenced locations within seven large plots originally surveyed, 1968-1970. In addition to raw count data of all bird species detected, we include information from distance sampling and time-interval sampling methods. To our knowledge, this is one of the only structured surveys of winter forest bird populations in the Coast Range Mountains, USA.

Physiological responses of Douglas-fir to climate and forest disturbances as detected by cellulosic carbon and oxygen isotope ratios.

Swiss needle cast (SNC), caused by a fungal pathogen, Nothophaeocryptopus gaeumannii, is a major forest disease of Douglas-fir (Pseudotsuga menziesii) stands of the Pacific Northwest (PNW). There is mounting concern that the current SNC epidemic occurring in Oregon and Washington will continue to increase in severity, frequency and spatial extent with future warming. Nothophaeocryptopus gaeumannii occurs wherever its host is found, but very little is known about the history and spatial distribution of SNC and its effects on growth and physiological processes of mature and old-growth forests within the Douglas-fir region of the PNW. Our findings show that stem growth and physiological responses of infected Douglas-fir to climate and SNC were different between sites, growth periods and disease severity based on cellulosic stable carbon and oxygen isotope ratios and ring width data in tree rings. At a coastal Oregon site within the SNC impact zone, variations in stem growth and Δ13C were primarily influenced by disproportional reductions in stomatal conductance (gs) and assimilation (A) caused by a loss of functioning stomates through early needle abscission and stomatal occlusion by pseudothecia of N. gaeumannii. At the less severely infected inland sites on the west slopes of Oregon's Cascade Range, stem growth correlated negatively with δ18O and positively with Δ13C, indicating that gs decreased in response to high evaporative demand with a concomitant reduction in A. Current- and previous-years summer vapor pressure deficit was the principal seasonal climatic variable affecting radial stem growth and the dual stable isotope ratios at all sites. Our results indicate that rising temperatures since the mid-1970s has strongly affected Douglas-fir growth in the PNW directly by a physiological response to higher evaporative demand during the annual summer drought and indirectly by a major SNC epidemic that is expanding regionally to higher latitudes and higher elevations.