Western Montana Research Articles

Finding fishers: determining fisher occupancy in the Northern Rocky Mountains

AbstractMonitoring rare and elusive carnivores is inherently challenging because they often occur at low densities and require more resources to effectively assess status and trend. The fisher (Pekania pennanti) is an elusive mesocarnivore endemic to North America; in its western populations it is classified as a species of greatest conservation need. During winter of 2018–2019, we deployed remotely triggered cameras in randomly selected, spatially balanced 7.5‐km × 7.5‐km grid cells across a broad study area in western Montana, Idaho, and eastern Washington, USA. As part of this large‐scale, multi‐state monitoring effort, we conducted an occupancy assessment of the Northern Rocky Mountain fisher population at a range‐wide scale. We used non‐spatial occupancy models to determine the current extent of fisher occurrence in the Northern Rocky Mountains and to provide baseline occupancy estimates across a broad study area and a refined sampling frame for future monitoring. We used a spatial occupancy model to determine patterns in fisher occurrence across their Northern Rocky Mountain range while explicitly correcting for spatially induced overdispersion. Additionally, we assessed factors that influenced fisher occurrence through covariate occupancy modeling that considered predicted fisher habitat, site‐level environmental characteristics, and the influence of available harvest records (incidental and regulated). We detected fishers in 32 out of 318 (10%) of our surveyed cells, and estimated that overall, 160 (14%; 95% CI = 115–218) of 1,143 grid cells were occupied by fishers. Fisher occupancy was positively associated with our stratum that contained cells with a greater proportion of predicted fisher habitat and with proximity to nearest 2000–2015 harvest location. Fisher occupancy was weakly and positively associated with increased canopy cover. Our spatial model identified 2 areas with higher predicted occupancy: a large area across the Idaho Nez Perce‐Clearwater National Forest, and a smaller area in the Cabinet Mountain Range crossing the northern border of Idaho and Montana. We used spatial occupancy results from our original sampling frame to create a biologically derived refined sampling frame for future monitoring. Within the bounds of our refined sampling frame, we estimated that 155 (22%; 95% CI = 110–209) of 700 grid cells were occupied by fishers. By incorporating our increasing understanding of fisher habitat with contemporary analytical techniques, we defined current range‐wide occupancy of the Northern Rocky Mountain fisher population, identified core areas of fisher occurrence for future conservation efforts, and used our model results to create a refined sampling frame for future fisher monitoring in the Northern Rocky Mountains.

Consequences of migratory strategy on habitat selection by mule deer

AbstractUngulate behavior is often characterized as balancing selection for forage and avoidance of predation risk. Within partially migratory ungulate populations, this balancing occurs across multiple spatial scales, potentially resulting in different exposure to costs and benefits between migrants and residents. We assessed how availability and selection of forage and risk from predators varied between summer ranges of migrant and resident mule deer (Odocoileus hemionus; a species in which individual migratory strategies are generally fixed for life) in 3 study areas in western Montana, USA, during summers 2017–2019. We hypothesized that mule deer would face a tradeoff between selecting forage and avoiding predation risk, and that migration and residency would pose contrasting availability of forage and risk at a broad (summer range) spatial scale. We hypothesized deer exposed to lower forage at a given spatial scale would compensate for reduced availability by increasing selection of forage at the cost of reduced avoidance of predators, a mechanism whereby migrants and residents could potentially achieve similar exposure to forage despite disparate availability. We compared the availability of forage (kcal/m2) and predation risk from wolves (Canis lupus) and mountain lions (Puma concolor) between summer ranges of each migratory strategy, then assessed how selection for those factors at the home range (second order) and within‐home range (third order) scales varied using resource selection functions (RSFs). As forage availability increased among mule deer summer ranges and individual home ranges, selection for forage decreased at the second‐order (P = 0.052) and third‐order (P = 0.081) scales, respectively, but avoidance of predators varied weakly. In 1 study area, summer range of residents contained lower forage and higher risk than summer range of migrants, but residents compensated for this disadvantage through stronger selection of forage and avoidance of risk at finer spatial scales. In the other 2 study areas, summer range of migrants contained lower forage and higher risk than residents, but migrants did not compensate through stronger selection for beneficial resources. The majority of mule deer in our study system were migratory, though the benefits of migration were unclear, suggesting partial migration may persist in populations even when exposure to forage and predation risk appears unequal between strategies.

Haskap Preharvest Fruit Drop and Stop-drop Treatment Testing

Haskap (Lonicera caerulea), also known as honeyberry, is a relatively new fruit crop in North America. To date, most academic activity and research in North America involving haskap has focused on cultivar development and health benefits, with relatively few field experiments providing information to guide field planning and harvest management for the recently released cultivars. In 2020, we documented preharvest fruit drop (PHFD) rates for 15 haskap cultivars planted in a randomized block design at our research center in western Montana with the aim of preliminarily determining whether certain cultivars may be prone to this phenomenon. Additionally, we evaluated two plant growth regulators (PGRs) to reduce PHFD in two cultivars previously observed to have high rates of PHFD. Results suggest cultivar-specific variations in PHFD near berry maturation. Because haskap harvest indices are not well-defined and may be cultivar-specific, we share our 1-year study results as preliminary information and as a call for further research. Cultivars Aurora, Boreal Blizzard, Borealis, Indigo Gem, Kapu, and Tana all had PHFD rates less than 12% of yield, where yield is the weight of berries lost to PHFD plus marketable yield and marketable yield is fruit remaining on the shrub at harvest. Cultivars Chito, Kawai, and Taka had the highest rates of PHFD, although marketable yields were still relatively high, especially for Kawai. We note that ease of fruit detachment is an important consideration in mechanical harvest, and this characteristic could be advantageous if managed appropriately. The PGRs evaluated (1-napthaleneacetic acid and aminoethoxyvinylglycine) did not influence PHFD rates; however, our study was limited by the sample size and by the lack of information regarding haskap abscission physiology. In summary, the haskap cultivars evaluated exhibited variable PHFD rates in the year of the study, and further research is needed to understand haskap fruit maturation, harvest indices, and abscission.

Rangeland application of biochar and rotational grazing interact to influence soil and plant nutrient dynamics

Few studies have been conducted to evaluate the use of wood biochar in temperate rangeland ecosystems and none have investigated the interactive influence of wood biochar and cattle trampling activity (associated with short-term rotational grazing) on soils and plants. We conducted a field study on a semi-natural pasture in western Montana, USA to evaluate how wood biochar, with or without short-term intensive trampling affected biochar incorporation depth, soil physicochemical properties, nutrient dynamics, and grass nutrient concentrations with a particular focus on nitrogen (N) and phosphorus (P). We hypothesized that cattle trampling alone would induce soil compaction and generally reduce soil nutrient cycling rates and/or availability, but the presence of biochar prior to trampling could improve soil aeration and grass nutrition. After three months, we found that trampling alone significantly increased surface soil bulk density and reduced the values of nearly all soil N metrics examined in this study; however, the application of biochar prior to trampling improved infiltration rate and increased net nitrification. Trampling also facilitated biochar incorporation into soils. Biochar additions significantly increased soil available organic P (i.e., enzyme extractable P) while reducing soil inorganic P (i.e., CaCl2-P, citrate-P) with or without trampling. Soil P responses appeared to be associated with biochar ortho-P sorption capacity and was more pronounced in soils that had undergone cattle trampling. Changes in soil P were reflected in grass P concentration after three months. Overall, our field study demonstrated that the use of biochar on rangeland soils with short-term rotational grazing could result in a neutral to positive effect on soil and plant nutrients.

Assessing the Role of Snow Cover for Post‐Wildfire Revegetation Across the Pacific Northwest

AbstractForested, mountain landscapes in the Pacific Northwest (PNW) are changing at an unprecedented rate, largely due to shifts in the regional climate regime. Documented climate warming trends across the PNW include increasing wildfire frequency and severity and an increasingly ephemeral snowpack, especially at moderate elevations. We analyzed 24 high severity wildfires across four distinct PNW mountainous subregions, examining snow‐vegetation relationships for two years pre‐fire and four years post‐fire. To assess the importance of snow cover for revegetation compared to other climatic, topographic, and burn severity‐related variables, binary regression tree models were constructed for the dominant pre‐fire conifer species within each of the four PNW subregions. Summer precipitation consistently appeared as the most important variable driving post‐fire revegetation across all four subregions. Snow cover variables (snow cover frequency and snow disappearance date), along with elevation, were shown to be secondary but significantly influential explanatory variables for revegetation in the Oregon and Washington Cascades. Revegetation was also analyzed using a time series of linear regressions across 200‐m elevation bands by measuring correlations between winter snow cover and summer vegetation greenness. Results showed strong positive post‐fire correlations at moderate elevations in the western Montana Rockies and at the lowest elevation band in the Idaho Rockies. Considering trends of increasing wildfire activity, lower snowpacks, and earlier snow disappearance dates across the PNW, forests will likely experience more frequent drought conditions that will impact post‐wildfire vegetation regrowth.

Fine-grained topographic diversity data improve site prioritization outcomes for bees

Biodiversity hotspots are often found in areas of high environmental diversity. This may be explained by an abundance of varying niche space promoting coexistence, buffering effects allowing for persistence during periods of climate change, and by a diversity of selective pressures driving speciation. Thus, environmentally diverse areas are attractive targets for conservation. Few aspects of the environment are unchanging, however, and strategies targeting comparatively durable surrogates for biodiversity are a focus of applied conservation research. For example, topographic diversity (topodiversity), or the variation of landforms present in an area, has proven useful for site prioritization among some taxa. The suitability of this approach for conservation of ecologically important taxa, such as bee pollinators, has not been studied exhaustively, however. Furthermore, the importance of topographic features smaller than 30 m is generally unknown, due to the limited availability of fine-grained elevation data, though could prove relevant for this group and others. We gathered sub-meter elevation data with structure-from-motion photogrammetry and surveyed for bees and plants in the Sapphire Mountains of western Montana, USA to explore if fine-grained topodiversity data are useful for site prioritization. We calculated topodiversity metrics for a range of spatial grain-sizes (0.25–250 m) and neighborhoods (1–500 m) and conducted sensitivity analyses studying correlations with biodiversity patterns. We prioritized sites according to rarity-weighted richness (RWR), which indicates complementarity, or the degree to which a site can contribute unique species to a preserve network. Bee RWR was most strongly correlated with 2 m grain topodiversity data (r 0.73), while plant RWR was most strongly correlated with 235 m data (r 0.44). Though 2 m data were optimal in bees, larger resolutions (35 m) also were effective for site prioritization and use of these meso-grained surrogates only increased site prioritization error by one rank position. We explored multiple regression models predicting RWR with topodiversity metrics of various grains and neighborhood but found no improvement over linear models incorporating only the single most correlated grain-size and neighborhood metric. The best model for plants performed relatively poorly for the task of bee site prioritization. Modeling complementarity with pooled biodiversity data aggregated from both groups slightly improved site rankings for bees and slightly decreased ranking performance in plants. While the costs of fine-grained elevational remote sensing technologies may be high at present, national efforts to gather these data are on the horizon and may facilitate conservation of bees and other groups at the local scale.

Tracking 40 Million Years of Migrating Magmatism across the Idaho Batholith Using Zircon U-Pb Ages and Hf Isotopes from Cretaceous Bentonites

Cretaceous strata preserved in Wyoming contain numerous large bentonite deposits formed from the felsic ash of volcanic eruptions, mainly derived from Idaho batholith magmatism. These bentonites preserve a near-continuous 40 m.y. chronology of volcanism and their whole-rock and mineral chemistry has been used to document igneous processes and reconstruct the history of Idaho magmatism as emplacement migrated across the Laurentian margin. Using LA-ICP-MS, we analyzed the U-Pb ages and Hf isotopic compositions of nearly 700 zircon grains from 44 bentonite beds from the Bighorn Basin, Wyoming. Zircon populations contain magmatic autocrysts and antecrysts which can be linked to the main pulses of the Idaho batholith and xenocrysts ranging from approx. 250 Ma to 1.84 Ga from country rocks and basement source terranes. Initial εHf compositions of Phanerozoic zircons are diverse, with compositions ranging from −26 to nearly +12. Based on temporal trends in zircon ages and geochemistry, four distinct periods of plutonic emplacement are recognized during the Mid- to Late Cretaceous that follow plutonic emplacement across the Laurentian suture zone in western Idaho and into western Montana with the onset of Farallon slab shallowing. Our data demonstrate the utility of using zircons in preserved tephra to track the regional-scale evolution of convergent margins related to terrane accretion and the spatial migration of magmatism related to changes in subduction dynamics.

Magmatism and Extension in the Anaconda Metamorphic Core Complex of Western Montana and Relation to Regional Tectonics

AbstractMetamorphic core complexes (MCCs) are a product of crustal extension, but their dynamics are still debated. Early research suggests that the formation of MCCs in the western United States was due to gravitational collapse of crust that had been thickened during Cordilleran orogenesis. However, the instability of overthickened crust alone cannot explain the diachronous formation of core complexes with a strong spatial dependency, as there was relatively uniform crustal thickness along strike of the Cordillera. For this reason, there is an interest in what role other lithospheric processes (such as subducted slab removal) play in the evolution of MCCs. We investigate the role of such processes by determining the temporal relation between magmatism and extension in the Anaconda MCC (AMCC) of western Montana. Geologic mapping, zircon U‐Pb geochronology, and zircon (U‐Th)/He thermochronology reveal that the initiation of extension in the AMCC in the Eocene (∼53 Ma) began at least 3 Myr after the emplacement of voluminous Paleocene two‐mica plutons. We interpret that the AMCC is an example of a core complex that was primed for extension by magmatic thermal weakening and suggest that foundering of the Farallon flat slab and the onset of the ignimbrite flareup in western Montana was responsible for the initiation of AMCC extension. An updated compilation of MCC cooling ages and Cenozoic volcanic activity across the western United States supports previous interpretations that the removal of Farallon oceanic lithosphere likely initiated MCC exhumation in some regions.

CEDAR WAXWINGS (BOMBYCILLA CEDRORUM) FEEDING ON BIRCH SAP AT RED-NAPED SAPSUCKER (SPHYRAPICUS NUCHALIS) SAP WELLS

In late June 2020 in western Montana we observed up to 10 Cedar Waxwings (Bombycilla cedrorum) feeding on tree sap at Red-naped Sapsucker (Sphyrapicus nuchalis) sap wells excavated on 2 limbs of a Water Birch (Betula occidentalis). These observations constitute (a) the 1st report of waxwings feeding at sap wells created by sapsuckers of any species; (b) the 1st report of waxwings feeding on tree sap in early summer; and (c) the 1st report of the consumption of birch sap by this waxwing species. The Cedar Waxwings may have sought tree sap because of the limited availability of early-summer sugary fruits at the time of our observations in combination with the presence of new clusters of sap wells created by at least 1 pair of sapsuckers near where the waxwings were beginning to breed. The prevalent sugars in birch sap (glucose, fructose) are also those most efficiently assimilated by Cedar Waxwings and may have contributed in attracting the waxwings to the sapsucker wells.

Behavior‐specific habitat models as a tool to inform ungulate restoration

AbstractAcross North America, many ungulate species that experienced historic population declines and range contractions are now broadly distributed across their native ranges after the implementation of successful restoration programs. The use of translocation continues to serve as an important restoration tool and is often informed through habitat models used to identify potential translocation areas based on biotic and abiotic landscape characteristics. Within the context of partially migratory wildlife populations, resident and migrant population segments can select for varying habitat characteristics, yet these population segments are often pooled when building habitat models. We used a large spatial dataset collected from eight bighorn sheep (Ovis canadensis) populations to build separate winter and summer resource selection models for migrant and resident animals with the purposes of (1) characterizing differences in seasonal selection patterns between resident and migrant population segments and (2) generating broad spatial predictions of bighorn sheep habitat to inform future translocations across western Montana, USA. Lastly, we used the model to inform two potential management scenarios, first to establish a new population in an unoccupied area and second to expand the distribution of existing populations through intra‐mountain translocations. Selection patterns were generally similar among migrants and residents, especially in winter. Summer selection patterns varied between the two behaviors, with migrants selecting for higher elevations and residents selecting for lower elevations. Throughout the western Montana prediction area, bighorn sheep habitat was centered around mountain areas in all seasons. In the first management scenario, our model predicted that adequate resident and migratory bighorn sheep habitat existed in the restoration area, thus justifying the use of either resident or migrant source populations in translocation. In the second management scenario, our model predicted that there was broad potential for translocations into unoccupied areas adjacent to the current bighorn sheep distribution in western Montana. The behavior‐specific approach to predicting bighorn sheep seasonal habitat captures the specific habitat characteristics of multiple migratory behaviors and may help to inform targeted and effective translocation programs.

Bagging Apple Fruit for Codling Moth Control in Western Montana

Codling moth (Cydia pomonella) is a major insect pest of apple (Malus domestica). If unmanaged, then codling moth can infest nearly all apples in an orchard, where the flesh-tunneling larva leave frass-laden tracks in the fruit. Insecticide-based management requires accurate application timing (typically based on adult moth and/or degree-day monitoring) and multiple spray applications. Both the season-long commitment to codling moth monitoring and management and limited familiarity with insecticides, application tools, and proper application procedures can prevent a small-scale or backyard grower from effectively limiting fruit damage. In addition, an increasing segment of growers is interested in nonchemical alternatives. Bagging fruitlets early in the season could be a simple and effective method of codling moth management for this subset of growers. At our research orchard in Corvallis, MT, we tested a method combining fruit thinning and bagging using plastic bags the first season and nylon bags the second season. Plastic bags reduced the incidence of codling moth damage to fruit from 34% to 10%, but european earwig (Forficula auricularia) frass, which was found in more than 50% of plastic-bagged apples, made harvesting the fruit unappealing. We tested nylon fruit bags during the second year of the study. These bags did not significantly reduce the incidence of codling moth. Both the soluble solids content and titratable acidity were higher in unbagged fruit during the second year of the study, whereas color measurements indicated bagged fruit were greener on the shaded side of the fruit. Failure of the nylon bags may have been attributable to eggs laid before bagging, eggs laid or larva burrowing through bagging, or improper bag application methods. Further research could assess whole-tree bags, the addition of rubber bands or twist ties when applying nylon bags, pretreatment of fruit with horticulture oil, and/or dipping nylon bags in kaolin clay before application; however, these steps add time and increase costs, which may discourage the small-scale fruit grower. Overall, results indicate that fruit bagging holds promise for codling moth management; however, further work is needed to optimize the methodology.

Habitat selection by wolves and mountain lions during summer in western Montana.

In the Northern Rockies of the United States, predators like wolves (Canis lupus) and mountain lions (Puma concolor) have been implicated in fluctuations or declines in populations of game species like elk (Cervus canadensis) and mule deer (Odocoileus hemionus). In particular, local distributions of these predators may affect ungulate behavior, use of space, and dynamics. Our goal was to develop generalizable predictions of habitat selection by wolves and mountain lions across western Montana. We hypothesized both predator species would select habitat that maximized their chances of encountering and killing ungulates and that minimized their chances of encountering humans. We assessed habitat selection by these predators during summer using within-home range (3rd order) resource selection functions (RSFs) in multiple study areas throughout western Montana, and tested how generalizable RSF predictions were by applying them to out-of-sample telemetry data from separate study areas. Selection for vegetation cover-types varied substantially among wolves in different study areas. Nonetheless, our predictions of 3rd order selection by wolves were highly generalizable across different study areas. Wolves consistently selected simple topography where ungulate prey may be more susceptible to their cursorial hunting mode. Topographic features may serve as better proxies of predation risk by wolves than vegetation cover-types. Predictions of mountain lion distribution were less generalizable. Use of rugged terrain by mountain lions varied across ecosystem-types, likely because mountain lions targeted the habitats of different prey species in each study area. Our findings suggest that features that facilitate the hunting mode of a predator (i.e. simple topography for cursorial predators and hiding cover for stalking predators) may be more generalizable predictors of their habitat selection than features associated with local prey densities.

Observations of River Solute Concentrations during Ice Formation

It has been observed in some aquatic systems, such as lakes and oceans, that when ice forms solutes are excluded from the ice, increasing their concentrations in the water. This process, known as solute ice exclusion, could be important in rivers and streams where ice can be a significant fraction of the total volume, potentially significantly increasing chemical concentrations in the water. There have been no reported observations of solute dynamics during ice formation in rivers and streams, however, even though the freeze–thaw cycle is a common phenomenon for lotic systems in cold regions. To investigate this process, a variety of solutes were measured during three ice formation events in a mine-waste-polluted river in western Montana. A laboratory study was also conducted to determine how different metal cations partition when ice forms. It was found that solute concentrations significantly increase during the early stages of ice formation. Correlations with ion size and changes in temperature support the idea that ice exclusion was controlling solute dynamics during these periods. These observations could have important implications for predicting the environmental impacts of toxic solutes in rivers and streams subject to seasonal ice formation.

Assessing the Potential for Pyroconvection and Wildfire Blow Ups

Fire meteorologists have few tools for assessing atmospheric stability in the context of wildfires. Most tools at our disposal were developed for assessing thunderstorms and general convection, and so they ignore heat and moisture supplied by the wildfire. We propose a simple parcel-based model that can be used to assess how the atmosphere will affect a growing wildfire plume by also taking into account the heat and moisture released from the fire. From this model, we can infer trends in day to day atmospheric stability as it relates to fire plumes. We can also infer how significant the appearance of a pyrocumulus cloud on the top of a fire column is. In some cases, the appearance of a pyrocumulus indicates that the fire is near if not already blowing up, whereas in other cases environmental conditions remain too stable to have a significant effect. A qualitative application of the model is demonstrated through application to a 2017 wildfire case in Western Montana.

Heterospecific competitors and seasonality can affect host physiology and behavior: key factors in disease transmission

AbstractEcological and environmental factors can influence the transmission of infectious diseases. They can accomplish this via effects on host susceptibility and exposure to infection, which are governed by host physiology and behavior, respectively. To better inform disease control, more information is needed about how extrinsic factors affect physiological and behavioral processes that determine transmission. We investigated how heterospecific competitors and seasonality may influence host susceptibility and intraspecific contact rates using a directly transmitted disease system, the North American deer mouse (Peromyscus maniculatus)—Sin Nombre hantavirus (SNV) system. In grasslands of western Montana, USA, deer mice compete with dominant voles (Microtus spp.) and shrews (Sorex spp.) and experience a seasonal temperate climate. Higher SNV transmission occurs primarily during spring/summer, when changes in physiology and behavior may serve as influential contributors. We hypothesized that (1) voles, and to a lesser extent shrews, will induce chronic stress, suppress immunity, and may change contact rates of deer mice; and (2) during spring/summer, deer mice may experience chronic stress, suppressed immunity, and higher contact rates, which may help explain the reported seasonality in SNV transmission. Over two years, we trapped small mammals at four grids in western Montana. Deer mice were sampled for feces and blood and evaluated for scar numbers, demography, and body condition scores (BCSs). We evaluated stress physiology with fecal corticosterone metabolites (FCMs), neutrophil/lymphocyte (N/L) ratios and BCSs, immunity with white blood cell (WBC) counts, and contact rates with scar numbers. We found that shrew density was negatively associated with stress response FCMs, suggestive of chronic stress. Additionally, although complex interactions existed, shrew and vole densities were negatively associated with BCSs, but differentially with scar numbers. N/L ratios were higher in spring/summer, whereas WBC counts were lower in summer, suggestive of chronic stress and suppressed immunity, respectively. Our results suggest that (1) heterospecific competitors may differentially influence disease transmission via stress physiology and contact rates, and that (2) chronic stress, suppressed immunity, and higher contact rates may help explain why higher SNV transmission has been previously reported during spring/summer in Montana. Our findings may extend to other directly transmitted disease systems.

Continuing Orthohantavirus Circulation in Deer Mice in Western Montana.

Hantavirus pulmonary syndrome (HPS) is an often-fatal disease caused by New World hantaviruses, such as Sin Nombre orthohantavirus (SNV). In the US, >800 cases of HPS have been confirmed since it was first discovered in 1993, of which 43 were reported from the state of Montana. The primary cause of HPS in the US is SNV, which is primarily found in the reservoir host Peromyscus maniculatus (deer mouse). The reservoir host covers most of the US, including Montana, where multiple studies found SNV in local deer mouse populations. This study aimed to check the prevalence of SNV in the deer mice at popular recreation sites throughout the Bitterroot Valley in Western Montana as compared to previous studies in western Montana. We found high prevalence (up to 20%) of deer mice positive for SNV RNA in the lungs. We were unable to obtain a SNV tissue culture isolate from the lungs but could passage SNV from lung tissue into naïve deer mice. Our findings demonstrate continuing circulation of SNV in western Montana.

Wildfire impacts on forest microclimate vary with biophysical context

AbstractIncreasing wildfire activity in western North America has the potential to remove forest canopy cover over large areas, increasing the vulnerability of understory plants and juvenile trees to microclimatic extremes. To understand the impacts of wildfire on forest microclimatic buffering, we monitored daily temperature and vapor pressure deficit (VPD) in 33 plots over the first two growing seasons following two wildfires from 2017. The Lolo Peak and Sunrise fires occurred during a regionally extensive fire season, burning mixed‐conifer and subalpine forests across complex mountainous topography in western Montana. Sensors were deployed from June to September in 2018 and 2019 in sites stratified by aspect, elevation, and fire severity (unburned, moderate, high) to capture a range of forest types, biophysical contexts, and fire effects. Loss of canopy and understory vegetation had marked effects on microclimate: On average, sites burned at high severity had 3.7°C higher daily maximum temperatures and 0.81 kPa higher daily maximum VPD relative to paired unburned sites. Differences between burned and unburned sites were most pronounced when ambient temperatures were high, across diurnal and seasonal time scales. Differences were also more pronounced at sites with less canopy cover, more bare ground postfire, and greater long‐term water availability (i.e., low climatic water deficit). Our results reveal fire‐caused changes in microclimate extremes that are biologically meaningful for the postfire establishment of tree seedlings and understory vegetation. These effects depend strongly on biophysical context, with cool‐wet forests more vulnerable to fire‐caused changes in microclimate compared with warm‐dry settings. Our results further highlight the functional importance of standing dead trees for moderating surface temperature in postfire environments. Anticipating forest ecosystem responses to increased warming and wildfire activity, and the potential for fire to catalyze vegetation changes, thus requires considering the substantial impacts of fire on microclimate.

Expanding number of Western US urban centers face declining summertime air quality due to enhanced wildland fire activity

Combining multiple sources of information on atmospheric composition, wildland fire emissions, and fire area burned, we link decadal air quality trends in Western US urban centers with wildland fire activity during the months of August and September for the years 2000–2019. We find spatially consistent trends in extreme levels (upper quantile) of fine particulate matter (PM2.5), organic carbon, and absorption aerosol optical depth centered on the US Pacific Northwest during the month of August. Emerging trends were also found across the Pacific Northwest, western Montana, and Wyoming in September. Furthermore, we identify potential wildfire emission ‘hotspots’ from trends in wildfire derived PM2.5 emissions and burned area. The spatial correspondence between wildfire emissions hotspots and extreme air quality trends, as well as their concomitant spatial shift from August to September supports the hypothesis that wildfires are driving extreme air quality trends across the Western US. We derive further evidence of the influence of wildland fires on air quality in Western US urban centers from smoke induced PM2.5 enhancements calculated through statistical modeling of the PM2.5-meteorology relationship at 18 Western US cities. Our results highlight the significant risk of increased human exposure to wildfire smoke in August at these Western US population centers, while also pointing to the potential danger of emerging trends in Western US population growth, wildfire emissions, and extreme air quality in September.

Early Cretaceous Provenance, Sediment Dispersal, and Foreland Basin Development in Southwestern Montana, North American Cordillera

AbstractThe Lower Cretaceous Kootenai Formation in western Montana records the onset of foredeep sedimentation in the Idaho‐Montana retroforeland basin of the North American Cordillera. Contrasting models for sediment dispersal during Early Cretaceous time have been proposed. We use sandstone petrography, large‐n (n = 600) detrital zircon U‐Pb geochronology, and mixture modeling to determine the provenance of the Kootenai Formation. These new data combined with additional data from the literature suggest three discrete provenance signatures. Type I sandstones are quartz‐rich with U‐Pb age peaks at ca. 158, 238, 410, 600, and 1,035 Ma; they were sourced from exhumed Jurassic continental strata and transported northward by axial drainages. Type II sandstones are lithic‐rich with U‐Pb age peaks at ca. 154, 166, 1,840, 1,920, 2,080, and 2,700 Ma; they were deposited by transverse rivers that drained exhumed lower‐middle Paleozoic strata from the Sevier belt. Type III sandstones contain feldspars and minor volcanic lithics with U‐Pb age spectra that are dominated by ca. 112 and 162 Ma ages; they were transported by transverse drainages that connected the hinterland of the orogen with the western Montana foreland. Based on provenance analysis of the Kootenai Formation, subtle Early Cretaceous thick‐skinned deformation in southwestern Montana did not exhume basement nor did it partition the foreland into locally sourced depocenters. Sediment sources for the western Montana foreland are consistent with those to the north in Alberta and different than southern Idaho. These data also provide insight into the translational history of terranes in the hinterland of the orogen during this time.

Large wood and sediment storage in a mixed bedrock-alluvial stream, western Montana, USA

Sediment storage by instream wood in forested mountain streams mediates sediment movement from hillslopes through the channel network and can alter channel morphology at multiple spatial scales. Mixed bedrock-alluvial channels are prevalent in mountain stream networks, yet the distribution and geomorphic impact of large wood within these streams are poorly understood. To estimate how the distribution of large wood in a mixed bedrock-alluvial stream relates to sediment storage, we measured and characterized large wood, and we surveyed the volume of associated sediment within a stream in the Bitterroot Mountains, Montana. The upstream portion of the study reach is predominantly alluvial and the downstream portion has significant bedrock exposure along the channel bed and banks. Wood volume and sediment storage in the mixed bedrock-alluvial subreach are 50% and 15%, respectively, of those measured in the alluvial subreach. Most wood is organized into jams, and two channel-spanning jams within the upstream subreach account for 50% and 80% of the reach-averaged wood and sediment volume, respectively. The volume of sediment stored by wood in the full reach is the same order of magnitude as the estimated annual bedload export. Our study highlights the interactions among channel form and the fluxes and storage of wood and sediment. Wood that forms channel-spanning jams, which store a disproportionate amount of wood and sediment in the study reach, may accentuate differences between alluvial and bedrock-dominated subreaches in mountain stream networks, by promoting sediment deposition and storage upstream and by reducing sediment supply to downstream reaches.