Cascade Range Research Articles

Burn severity and pre-fire seral state interact to shape vegetation responses to fire in a young, western Cascade Range forest

Wildfire size and frequency are increasing across the western U.S., affecting large areas of young, second-growth forest originating after logging and burning. Despite their prevalence in the western Cascade landscape, we have a poor understanding of how these young stands respond to fire or how their responses differ from older, undisturbed forests, which are well studied. We explore these questions using pre- and early post-fire data from a young (<30-year-old), naturally regenerating forest in western Oregon that was burned preemptively to limit spread of the 2018 Terwilliger Fire. We exploit natural variation in the initial vegetation and fire behavior to test how pre-fire seral state (relative abundance of early-seral vs. forest-generalist species) and burn severity interact to shape short-term responses to fire. Drawing from disturbance theory and studies of fire in older forests we hypothesized that pre-fire seral state would mediate compositional change and functional-group cover and richness through the regenerative and clonal traits of available species. Two years after fire, we found greater compositional change with increasing fire severity, although the effect was weaker where early-seral species dominated prior to burning. Species richness was unaffected by increasing fire severity as gains in early-seral species were balanced by loss of forest species. In contrast, species diversity (Hill’s N1) and evenness declined, reflecting a shift in the dominance structure of the understory, with the pre-fire dominant, Pteridium aquilinum, expanding further, and forest generalists declining. Among plant functional groups, both annuals and perennials responded positively to fire severity, but annuals remained sparse (<1% of herbaceous cover), a stark contrast to their dominance after fire in older forests. Increasing fire severity enhanced the cover and richness of early-seral herbs. However, it reduced the cover or richness of most other groups, including early-seral shrubs, forest herbs, and forest shrubs. Within most functional groups, species varied in their responses to fire, reflecting variation in the type and depth of burial of perennating structures and in the potential for clonal growth. Our results underscore the importance of pre-fire conditions for shaping understory responses to fire in young forests, as they do in older forests. Legacies of past disturbance and species’ adaptions to fire clearly favor early-seral herbs over residual forest species. Further study is needed to determine whether the recurrence of fire during the early stages of stand development simply resets succession or alters its longer-term trajectory.

Evidence for niche conservatism in alpine beetles under a climate‐driven species pump model

AbstractAimPast glacial cycles have generated lineage diversity in alpine habitats, acting as a climate‐driven species pump. It is not clear how much this process contributes to ecological diversification of alpine species. To examine this problem, we test patterns of genetic and phenotypic divergence in two co‐distributed species complexes of flightless alpine ground beetles. Greater differentiation in functional traits would indicate that ecological selection is an outcome of oscillating climate change, whereas greater differentiation in non‐ecological traits would indicate niche conservatism.LocationThe Cascades Range and Trinity Mountains of western North America.TaxonNebria paradisiandN.vandykeispecies complexes (Insecta: Coleoptera: Carabidae: Nebriinae).MethodsWe generated genome‐wide single nucleotide polymorphism data and mitochondrial sequence data, as well as morphological and physiological data, to compare populations spanning the range of both species. Phylogenetic and population genetic analyses were used to infer relationships among taxa and populations in each species complex, as well as historical demography. Support vector machines were used to test for classification of taxa and populations based on ecomorphological, ecophysiological and male reproductive traits. Mantel tests were then used to assess associations between phenotypic and genetic divergence among populations.ResultsTheN.vandykeiandN.paradisispecies complexes are each comprised of genetically distinctive populations exhibiting long‐term demographic declines. Each phylogeny supports multiple monophyletic groups with geographical cohesion. By examining phenotypic traits among populations in both species’ complexes, we show that reproductive trait divergence can discriminate species and population status more effectively than ecomorphological or ecophysiological traits. Reproductive and genetic divergence are significantly correlated in theN.vandykeispecies complex.Main ConclusionsWe found limited evidence of ecological selection acting on functional traits. Instead, reproductive and genetic divergence evolved among isolated populations in both species complexes, suggesting niche conservatism may be a common outcome in alpine species diversification.

Differences in the transient responses of individual glaciers: a case study of the Cascade Mountains of Washington State, USA

AbstractMountain glaciers have response times that govern retreat due to anthropogenic climate change. We use geometric attributes to estimate individual response times for 383 glaciers in the Cascade mountain range of Washington State, USA. Approximately 90% of estimated response times are between 10 and 60 years, with many large glaciers on the short end of this distribution. A simple model of glacier dynamics shows that this range of response times entails consequential differences in recent and ongoing glacier changes: glaciers with decadal response times have nearly kept pace with anthropogenic warming, but those with multi-decadal response times are far from equilibrium, and their additional committed retreat stands well beyond natural variability. These differences have implications for changes in glacier runoff. A simple calculation highlights that transient peaks in area-integrated melt, either at the onset of forcing or due to variations in forcing, depend on the glacier's response time and degree of disequilibrium. We conclude that differences in individual response times should be considered when assessing the state of a population of glaciers and modeling their future response. These differences in response can arise simply from a range of different glacier geometries, and the same basic principles can be expected in other regions as well.

Mitochondrial capture and subsequent genetic divergence generates a novel haplogroup: evidence from ancient and ongoing hybridization in mule and white-tailed deer

AbstractOdocoileus virginianus (white-tailed deer) and O. hemionus (mule deer) are sympatric across much of North America. Molecular evidence suggests that up to 24% of individuals in some populations are a product of hybrid ancestry. Several studies have alluded to ancient and recent introgression between Odocoileus spp.; however, no divergence dates were proposed. Herein, phylogenetic analyses of DNA sequences obtained from the mitochondrial Cytochrome b gene in 690 individuals identified three clades corresponding to black-tailed deer, white-tailed deer, or a unique combination of both white-tailed deer and mule deer. White-tailed deer and mule deer diverged from a common ancestor of approximately 3.13 mya followed by an ancient hybridization event of approximately 1.32 mya, in which the white-tailed deer mitochondrial genome was “captured” by mule deer. This hybridization event produced a novel haplogroup for white-tailed deer and mule deer located west of the Appalachian Mountains and east of the Cascade Range, south to Veracruz, Mexico, and north to the Yukon Territory, Canada. The ancestral mule deer-like mitochondrial genome appears to be restricted to black-tailed deer distributed along the western portion of the Cascade and Sierra Nevada Ranges of the United States and Canada, whereas the ancestral white-tailed deer-like mitochondrial genome is restricted to the eastern United States and portions of Latin America and Caribbean regions. The “captured mitochondrial genome” has continued on an independent evolutionary trajectory and represents a unique and broadly distributed haplogroup that is 7.25% and 2.84% different from the ancestral mule deer and ancestral white-tailed deer haplogroups, respectively.

Mapping Glacier Ablation With a UAV in the North Cascades: A Structure-from-Motion Approach

The glaciers of the North Cascades have experienced mass loss and terminus retreat due to climate change. The meltwater from these glaciers provides a flux of cold glacier meltwater into the river systems, which supports salmon spawning during the late summer dry season. The Nooksack Indian Tribe monitors the outlet flow of the Sholes Glacier within the North Cascades range with the goal of understanding the health of the glacier and the ability of the Tribe to continue to harvest sustainable populations of salmon. This study compares the UAV derived glacier ablation with the discharge data collected by the Tribe. We surveyed the Sholes Glacier twice throughout the 2020 melt season and, using Structure-from-Motion technology, generated high resolution multispectral orthomosaics and Digital Elevation Models (DEMs) of the glacier on each of the survey dates. The DEMs were differenced to reveal the surface height change of the glacier. The spectral data of the orthomosaics were used to conduct IsoData unsupervised classification. This process divided the survey area into Snow, Ice, and Rock classes that were then used to attribute the surface height changes of the DEMs to either snow or ice melt. The analysis revealed the glacier lost an average thickness of −0.132 m per day (m d−1) with snow and ice losing thickness at similar rates, −0.130 m d−1 and −0.132 m d−1 respectively. DEM differencing reveals that a total of −550,161 ± 45,206 m3 water equivalent (w.e.) was discharged into Wells Creek between the survey dates whereas the stream gauge station measured a total discharge of 350,023 m3. This study demonstrates the ability to spectrally classify the UAV data and derive discharge measurements while evaluating the small-scale spatial variability of glacier melt. Assessing ablation in small alpine glaciers is of great importance to downstream communities, like the Nooksack Indian Tribe who seek to understand the magnitude and timing of glacier melt in order to better protect their salmon populations. With this paper, we provide a baseline for future glacier monitoring and the potential to connect the snow surface properties with the rate of snow melt into a warming future.

MTEP, a Selective mGluR5 Antagonist, Had a Neuroprotective Effect but Did Not Prevent the Development of Spontaneous Recurrent Seizures and Behavioral Comorbidities in the Rat Lithium–Pilocarpine Model of Epilepsy

Metabotropic glutamate receptors (mGluRs) are expressed predominantly on neurons and glial cells and are involved in the modulation of a wide range of signal transduction cascades. Therefore, different subtypes of mGluRs are considered a promising target for the treatment of various brain diseases. Previous studies have demonstrated the seizure-induced upregulation of mGluR5; however, its functional significance is still unclear. In the present study, we aimed to clarify the effect of treatment with the selective mGluR5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]-pyridine (MTEP) on epileptogenesis and behavioral impairments in rats using the lithium–pilocarpine model. We found that the administration of MTEP during the latent phase of the model did not improve survival, prevent the development of epilepsy, or attenuate its manifestations in rats. However, MTEP treatment completely prevented neuronal loss and partially attenuated astrogliosis in the hippocampus. An increase in excitatory amino acid transporter 2 expression, which has been detected in treated rats, may prevent excitotoxicity and be a potential mechanism of neuroprotection. We also found that MTEP administration did not prevent the behavioral comorbidities such as depressive-like behavior, motor hyperactivity, reduction of exploratory behavior, and cognitive impairments typical in the lithium–pilocarpine model. Thus, despite the distinct neuroprotective effect, the MTEP treatment was ineffective in preventing epilepsy.

Advanced Nonlinear Control of Single Phase Shunt Active Power Filter Based on Full Bridge Dual Buck Converter

An advanced nonlinear control design of a single phase shunt active power filter based on a full bridge dual buck converter (FBDB-SAPF) is presented in this paper. The main control objectives are: i) compensation of harmonics and reactive power consumed by nonlinear loads aiming at satisfying a near unity power factor at the grid side, ii) regulation of the dc bus voltage to a desired value. To meet the above objectives, the proposed controller has two loops in cascade. The sliding mode approach based on the average state system is used in the inner loop for dealing with the compensation issue and performing PFC. In the outer loop, a filtered proportional-integral is applied to regulate the dc bus voltage of the FBDB-SAPF. The performance of the closed-loop system is tested via Matlab/ SimPowerSystems. The obtained results prove that the suggested controller achieves its objectives and demonstrate its efficiency in terms of tracking and robustness in front of parameter uncertainty.

Effects on Soil Temperature, Moisture, and Soil Respiration Two Years Following Intensive Organic Matter and Compaction Manipulations in the Oregon Cascades

Effects on Soil Temperature, Moisture, and Soil Respiration Two Years Following Intensive Organic Matter and Compaction Manipulations in the Oregon Cascades

Modeling of an unmanned aerial vehicle and trajectory tracking control using backstepping approach

A quadcopter is a type of unmanned under-actuated aerial vehicle (UAV) that has four arms, each connected to a motor (Hussein, 2020). It is an excellent platform for research on control, due to its high non-linearity and the high degree of coupling in its dynamic representation of the model. This paper deals with the modeling of this nonlinear system using the Newton-Euler formalism, combining the dynamics of translation and rotation of the vehicle. The control objective is to track the reference trajectory by managing altitude and attitude at the same time. A control structure based on two cascade loops is developed using the nonlinear Backstepping approach with Lyapunov's stability theory. Simulation results in Matlab/Simulink show that the control objective is met.

Characterization of Lower and Middle Pleistocene tephra beds in the southern plains of western Canada

Wellsch Valley tephra, near Swift Current, southwestern Saskatchewan, and Galt Island tephra, near Medicine Hat, southeastern Alberta, have been referenced in the literature since the 1970s, but little is available on their physical and chemical attributes — necessary information if they are to be recognized elsewhere. This study seeks to remedy this situation. Both have a calc-alkaline rhyolitic composition with hornblende, biotite, plagioclase, pyroxene, and Fe–Ti oxides being dominant. They have a similar composition but are not the same. Wellsch Valley tephra has a glass fission-track age of 0.75 ± 0.05 Ma, a reversed magnetic polarity, and was deposited at the close of the Matuyama Chron. Galt Island tephra has an age of 0.49 ± 0.05 Ma, a normal magnetic polarity, and was deposited during the early Brunhes Chron. Rich fossil vertebrate faunas occur in sediments close to them. Major- and trace-element concentrations in their glass shards indicate a source in the Cascade Range of the Pacific Northwest, USA, but differences in trace-element ratios suggest they are not consanguineous.

Role of PLCG2 in Aβ clearance and synaptic pruning.

The microglial mediated neuroinflammatory system has emerged as a major contributor to the molecular and phenotypic changes observed in the AD brain, including excessive synaptic loss (synaptic pruning) and decreased Aβ clearance (Heneka et al., 2015). GWAS studies have identified a number of novel rare coding variants for late-onset AD (LOAD) in microglial-associated genes (Sims et al., 2017). Notably, a single nucleotide polymorphism in the phospholipase C-gamma 2 gene (PLCγ2) (Pro522Arg) was found to be protective against LOAD (Magno et al., 2019). PLCγ2 hydrolyses the membrane phospholipid PIP2 (1-phosphatidyl-1D-myo-inositol 4,5-bisphosphate) to the secondary messengers IP3 (myo-inositol 1,4,5-trisphosphate) and DAG (diacyl-glycerol) activating a wide range of downstream signalling cascades (Bunney and Katan, 2011). However, how the P522R variant of PLCg2 attenuates pathologic insult in AD remains unknown. This study investigates the role of PLCg2 in Ab clearance and synaptic pruning using BV2 (mouse microglia) cells. The P552R variant was inserted into the human PLCγ2-myc-DDK (WT) construct (OriGene; RC200442), using Q5 site-directed mutagenesis (NEB, E0554S). BV2 cells were transfected with control (scrambled), WT (522P) or 522R variant PLCg2 using lipofectamine-2000. 48hrs post transfection cells were incubated with fluorescently labelled Ab or synaptosomes (purified from mouse brain) for 1hr. After 10 min of membrane and DAPI staining, cells were imaged using a Nikon A1R confocal microscope. Relative mRNA and protein expression levels were measured using qPCR and western blot. Over-expression of PLCg2 resulted in a robust increase in Ab uptake compared to the control (Fig 1F,H&I), and this was mildly enhanced in cells expressing the P552R variant. Conversely, synaptosome uptake was significantly reduced in BV2 cells over expressing PLCg2 and this reduction was again mildly enhanced in cells expressing the P552R variant (Fig 1E,G&I). Our study highlights the protective capacity of microglia in AD to modulate Ab clearance and synaptic pruning. We show that PLCg2 plays a key role in differentially regulating Ab and synaptosome uptake, and this regulation may be modified by the P552R variant. Increasing Ab uptake while minimising synaptosome loss is a key goal in the treatment of AD, hence PLCg2 may be an ideal therapeutic target.

Tree-ring history of Swiss needle cast impact on Douglas-fir growth in Western Oregon: correlations with climatic variables.

The fungal pathogen, Nothophaeocryptopus gaeumannii, occurs wherever Douglas-fir is found but disease damage is believed to be limited to the Coast Range and is of no concern outside the coastal fog zone (Shaw, et al., 2011). However, knowledge remains limited on the history and spatial distribution of Swiss Needle Cast (SNC) impacts in the Pacific Northwest (PNW). We reconstructed the history of SNC impacts on mature Douglas-fir trees based on tree ringwidth chronologies from the west slope of the Coast Range to the high Cascades of Oregon. Our findings show that SNC impacts on growth occur wherever Douglas-fir is found in western Oregon and is not limited to the coastal fog zone. The spatiotemporal patterns of growth impact from SNC disease were synchronous across the region, displayed periodicities of 25-30 years, strongly correlated with winter and summer temperatures and summer precipitation, and matched the patterns of enriched cellulosic stable carbon isotope indicative of physiological stress. While winter and summer temperature and summer precipitation influenced pathogen dynamics at all sites, the primary climatic factor of these three limiting factors varied spatially by location, topography, and elevation. In the 20th century, SNC impacts at low- to mid-elevations were least severe during the warm phase of the Pacific Decadal Oscillation (PDO, 1924-1945) and most severe in 1984-1986, following the cool phase of the PDO (1945-1977). At high elevations on the west slope of the Cascade Mountains, SNC impacts were the greatest in the 1990s and 2000s, a period of warmer winter temperatures associated with climate change. Warmer winters will likely continue to increase SNC severity at higher elevations, north along the coast from northern Oregon to British Columbia, and inland where low winter temperatures currently limit growth of the pathogen. Surprisingly, tree-ring records of ancient Douglas-fir logs dated ~53K radioactive years B.P. from Eddyville, OR displayed 7.5- and 20-year periodicities of low growth, similar to those found in modern day coastal Douglas-fir tree-ring records which we interpret as being due to cyclic fluctuations in SNC severity. Our findings indicate that SNC has persisted for as long as its host, and as a result of changing climate, may become a significant forest health problem in areas of the PNW beyond the coastal fog zone.

Quaternary basaltic volcanic fields of the American Southwest

AbstractThe southwestern United States contains numerous monogenetic basaltic volcanoes distributed in intraplate volcanic fields. We review, on a regional scale, our current understanding of the Quaternary basalts with a focus on aspects pertinent to hazard assessment, such as physical volcanology and geochronology, while also summarizing the several petrogenetic conceptual models that have been proposed for the range of local tectonic settings in the region. We count 2229 volcanoes in 37 volcanic fields (including the Pinacate volcanic field, which is mostly in northern Sonora, Mexico). Volcanic landforms are dominantly scoria cones and ramparts with attendant lava fields that have a spectrum of ‘a'ā and blocky to pāhoehoe morphologies, while a small percentage of the volcanoes are maars and tuff cones. Explosive eruption styles that were driven mainly by magmatic volatiles, where they have been studied in detail, included Hawaiian, Strombolian, violent Strombolian, and sub-Plinian activity. The latter two have resulted in substantial fallout deposits that can be traced tens of kilometers from source vents. Phreatomagmatic styles have produced pyroclastic current (mainly pyroclastic surges), ballistic, and fallout deposits. These eruption styles pose hazards to humans when they occur in populated areas and to air travel and regional infrastructure even in sparsely populated areas. All but one of the major volcanic fields (fields that contain ∼100 or more Quaternary volcanoes) together form a northwest-southeast–trending band, which we suggest may reflect an influence of plate-boundary-related shearing on melt segregation in the upper mantle along with other factors; this view is consistent with recent global positioning system (GPS) and structural geologic data indicating the influence of dextral motion along the North America-Pacific plate boundary deep inside the Southwest. Of the 2229 Quaternary volcanoes identified, ∼548 (25%) have been dated, and only ∼15% have been dated with methods such as 40Ar/39Ar and cosmogenic surface exposure methods that are considered optimal for young basalts. Acknowledging the large uncertainty due to the poor geochronological data coverage, we use a simple Poisson model to provide a first-order estimate of recurrence rates of monogenetic volcanoes on the scale of the region as a whole; recurrence rates using our compiled age data set range from 3.74 × 10−4 yr−1 to 8.63 × 10−4 yr−1. These values are only based on dated and mapped volcanoes, respectively, and do not account for undated and buried volcanoes or other uncertainties in the volcano count. The time between monogenetic eruptions in the Southwest is similar to the repose times of some polygenetic volcanoes, which suggests that the regional hazard is potentially commensurate with the hazard from a reawakening stratovolcano such as those in the Cascade Range. Notable in our review is that only a few volcanoes have been the subject of physical volcanological characterization, interpretation, and detailed petrologic study that may elucidate factors such as magma generation, ascent (including time scales), and controls on eruption style.

Considering the Revolution

Considering the Revolution

Linear Quadratic Regulator Based Smooth Transition Between Microgrid Operation Modes

Dual mode operation capability of distributed energy resources in microgrids is an attractive feature that makes these systems a promising solution for improving reliability and economy of the power system. However, the transition between microgrid operation modes (grid-connected and islanding) may lead to a significant deviation in voltage and current because of inconsistency in phase, frequency, and voltage amplitude. To minimize the fluctuations and provide a smooth transition, this paper presents an optimal control framework based on linear quadratic regulator. The framework includes two regulators that separately designed for each transition mode: 1) grid-connected to islanding smooth regulator, and 2) islanding to grid-connected smooth regulator. Optimality based on optimizing solution, smooth transition, ease of implementation due to its simple state feedback form and compatibility with familiar cascade loops are the main advantages of the proposed approach. Experimental results are presented to validate the efficacy of the proposed approach.

U-Pb Geochronology and Hf Isotope Geochemistry of the Turtleback Complex and East Sound Group, San Juan Islands, Northwestern North American Cordillera

Abstract This study focuses on Paleozoic rocks of the Turtleback Complex (TBC) and East Sound Group (ESG) of northwestern Washington. These assemblages record a long and complex history of magmatism, sedimentation, and volcanism as part of the Chilliwack composite terrane. This study investigates the tectonic setting and magmatic evolution of the Chilliwack terrane by analyzing U-Pb geochronologic and Hf isotopic data from zircons extracted from igneous and sedimentary rocks of the TBC and ESG. Igneous rocks of the TBC yield U-Pb ages of ~420-~370 Ma for zircon rims, which are interpreted to record pluton crystallization, and ages of ~500-370 Ma for inherited cores and antecrysts. Zircons older than 410-400 Ma yield typical igneous values of U/Th and U concentration and somewhat more evolved εHft values (+5 to +10), whereas younger grains yield values of U/Th and U concentrations that record ongoing metamorphism and have more juvenile εHft values of +10 to +15. This evolution is interpreted to have occurred in a long-lived island arc that experienced a transition at ~410-400 Ma from crustal thickening to regional crustal extension. Detrital zircon grains from the ESG yield dominant ages of ~421-~366 Ma and εHft values of +8 to +15, both of which overlap with values from igneous rocks of the underlying TBC. Strata of the ESG also contain abundant older zircon grains, with a dominant age peak of ~1860 Ma and subordinate peaks at 2673, 2570, 1485, 1113, 736, and 553 Ma. When compared with similar results from other assemblages and terranes in the northern Cordillera, our results suggest possible connections with the Yellow Aster Complex of the nearby North Cascade Range. Our results also suggest general similarities with the Alexander terrane, Wrangellia terrane, and southeast Alaska portion of the Yukon-Tanana terrane. These similarities are consistent with previous interpretations that the Chilliwack composite terrane formed in association with the Alexander, Wrangellia, and southeast Alaska portion of the Yukon-Tanana terrane along the paleo-Arctic margin of Laurentia during early Paleozoic time. Our work also illustrates the importance of recycling of older magmatic rocks over millions of years within a juvenile island arc system.

The selective degradation of sirtuins via macroautophagy in the MPP+ model of Parkinson\u2019s disease is promoted by conserved oxidation sites

The sirtuin (SIRT) protein family has been of major research interest over the last decades because of their involvement in aging, cancer, and cell death. SIRTs have been implicated in gene and metabolic regulation through their capacity to remove acyl groups from lysine residues in proteins in an NAD+-dependent manner, which may alter individual protein properties as well as the histone–DNA interaction. Since SIRTs regulate a wide range of different signaling cascades, a fine-tuned homeostasis of these proteins is imperative to guarantee the function and survival of the cell. So far, however, how exactly this homeostasis is established has remained unknown. Here, we provide evidence that neuronal SIRT degradation in Parkinson’s disease (PD) models is executed by autophagy rather than the proteasome. In neuronal Lund human mesencephalic (LUHMES) cells, all seven SIRTs were substrates for autophagy and showed an accelerated autophagy-dependent degradation upon 1-methyl-4-phenylpyridinium (MPP+) mediated oxidative insults in vitro, whereas the proteasome did not contribute to the removal of oxidized SIRTs. Through blockade of endogenous H2O2 generation and supplementation with the selective radical scavenger phenothiazine (PHT), we could identify H2O2-derived species as the responsible SIRT-oxidizing agents. Analysis of all human SIRTs suggested a conserved regulatory motif based on cysteine oxidation, which may have triggered their degradation via autophagy. High amounts of H2O2, however, rapidly carbonylated selectively SIRT2, SIRT6, and SIRT7, which were found to accumulate carbonylation-prone amino acids. Our data may help in finding new strategies to maintain and modify SIRT bioavailability in neurodegenerative disorders.

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.

The September 2020 Wildfires over the Pacific Northwest

AbstractA series of major fires spread across eastern Washington and western Oregon starting on September 7, 2020, driven by strong easterly and northeasterly winds gusting to ~70 kt at exposed locations. This event was associated with a high-amplitude upper-level ridge over the eastern Pacific and a mobile trough that moved southward on its eastern flank. The synoptic environment during the event was highly unusual, with the easterly 925-hPa wind speeds at Salem, Oregon, being unprecedented for the August-September period. The September 2020 wildfires produced dense smoke that initially moved westward over the Willamette Valley and eventually covered the region. As a result, air quality rapidly degraded to hazardous levels, representing the worst air quality period of recent decades. High-resolution numerical simulations using the WRF model indicated the importance of a high-amplitude mountain wave in producing strong easterly winds over western Oregon.The dead fuel moisture levels over eastern Washington before the fires were typical for that time of the year. Along the western slopes of the Oregon Cascades, where the fuels are largely comprised of a dense conifer forest with understory vegetation, fire weather indices were lower (moister) than normal during the early part of the summer, but transitioned to above-normal (drier) values during August, with a spike to record values in early September coincident with the strong easterly winds.Forecast guidance was highly accurate for both the Washington and Oregon wildfire events. Analyses of climatological data and fuel indices did not suggest that unusual pre-existing climatic conditions were major drivers of the September 2020 Northwest wildfires.

Drivers of productivity differences between Douglas-fir planted within its native range in Oregon and on exotic sites in New Zealand

Forest species planted outside their native range sometimes exhibit growth rates that far exceed those in their native range. In species grown for timber production, the improved growth in certain exotic environments has led to the widescale propagation of some outstanding species, but the proposed mechanistic drivers behind this improved growth are little studied. Given the increasing importance of understanding growth response to climate changes, many of these species present ideal test cases, including coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), a widely planted timber species native to the Pacific Coast of North America. We identified a set of seven sites in the Oregon Cascades Range and the South Island of New Zealand that were planted with Douglas-fir seedlings originating from a shared seed source in 2004, presenting an opportunity to examine drivers of productivity while reducing the confounding effect of genetics. We sampled plots at each of these sites during the 2019 dormant season by measuring standing trees, collecting increment cores, assessing soil conditions, and installing meteorological instruments. Using these data, we constructed an environmentally sensitive model of annual radial growth of the stem at breast height, accounting for between- and within-location variation controlled by environmental factors. Trees at New Zealand locations had increased diameter growth compared to those in Oregon. Lower vapor pressure deficit during the growing season was the primary cause of this improved productivity in New Zealand through presumed effects on higher stomatal conductance and net photosynthesis. In contrast, other environmental factors were identified as driving productivity differences between sites within Oregon and within New Zealand.