Central Rocky Research Articles

Testing tree-ring cellulose δ18O with water isotopes for Holocene lake δ18O interpretations in the central Rocky Mountains USA

Stable isotopes of water preserved in geologic archives, primarily as oxygen (δ18O), have proven critical for documenting Earth’s climatic and hydrologic systems past and present. However, timescale differences of water isotope inputs to proxy systems and the signal embedded in long paleorecords often confound translation to observed hydroclimatic metrics. Here, a unique 20-year dataset of meteorology, hydrology, and the isotopic composition of weekly meteoric and surface water samples (δ18O, δ2H) are combined with paleoclimate δ18O data from tree-ring cellulose and lake carbonate to better understand proxy signals of Upper Colorado river basin drought. Annual tree-ring cellulose δ18O from Picea engelmannii growing within a glacier-fed creek and a spring discharge area were used to derive annual source water δ18O using a cellulose source-water isotope model. Comparisons with the monitoring record indicates that tree-ring cellulose δ18O tracks variations in wet and dry hydroclimatic extremes. Source water isotopes are shown to reflect the hydroclimate of the current year and some number of previous years as an effective moisture-discharge proxy rather than a precipitation isotope proxy. Results contextualize Holocene lake carbonate δ18O data. The contemporary-to-paleo comparison identifies changes in seasonal precipitation extremes during recent millennia and several earlier arid and monsoon-dominated Holocene periods that exceed the arid maximum of the calibration period.

Precipitation Proxies for Flash Flooding: A Seven-Year Analysis over the Contiguous United States

Abstract Flash flooding remains a challenging prediction problem, which is exacerbated by the lack of a universally accepted definition of the phenomenon. In this article, we extend prior analysis to examine the correspondence of various combinations of quantitative precipitation estimates (QPEs) and precipitation thresholds to observed occurrences of flash floods, additionally considering short-term quantitative precipitation forecasts from a convection-allowing model. Consistent with previous studies, there is large variability between QPE datasets in the frequency of “heavy” precipitation events. There is also large regional variability in the best thresholds for correspondence with reported flash floods. In general, flash flood guidance (FFG) exceedances provide the best correspondence with observed flash floods, although the best correspondence is often found for exceedances of ratios of FFG above or below unity. In the interior western United States, NOAA Atlas 14 derived recurrence interval thresholds (for the southwestern United States) and static thresholds (for the northern and central Rockies) provide better correspondence. The 6-h QPE provides better correspondence with observed flash floods than 1-h QPE in all regions except the West Coast and southwestern United States. Exceedances of precipitation thresholds in forecasts from the operational High-Resolution Rapid Refresh (HRRR) generally do not correspond with observed flash flood events as well as QPE datasets, but they outperform QPE datasets in some regions of complex terrain and sparse observational coverage such as the southwestern United States. These results can provide context for forecasters seeking to identify potential flash flood events based on QPE or forecast-based exceedances of precipitation thresholds. Significance Statement Flash floods result from heavy rainfall, but it is difficult to know exactly how much rain will cause a flash flood in a particular location. Furthermore, different precipitation datasets can show very different amounts of precipitation, even from the same storm. This study examines how well different precipitation datasets and model forecasts, used by forecasters to warn the public of flash flooding, represent heavy rainfall leading to flash flooding around the United States. We found that different datasets have dramatically different numbers of heavy rainfall events and that high-resolution model forecasts of heavy rain correspond with observed flash flood events about as well as precipitation datasets based on rain gauge and radar in some regions of the country with few observations.

Folsom obsidian conveyance at the Great Divide Paleoindian sites, Wyoming

We present a study of obsidian artifacts found in Folsom contexts from the Great Divide Paleoindian sites (Great Divide Basin, Wyoming) to evaluate Paleoindian mobility patterns in the central and southern Rocky Mountains. Obsidian sourcing using pXRF demonstrates conveyance from Obsidian Cliff (400 km), Teton Pass (300 km), and the Green River/Engineer Quarry source. Other chipped stone raw materials from Folsom localities derive from sources in the upper Green River Basin, thus partially establishing a Folsom mobility pattern between the Yellowstone Plateau, upper Green River Basin, and Great Divide Basin of Wyoming. This study supports the notion that Paleoindians regularly transported lithic raw materials great distances even in relatively raw material rich regions like the interior of the Rocky Mountains and is further evidence for a sparsely documented Younger Dryas-aged use of the Yellowstone Plateau.

Old-Aged groundwater contributes to mountain hillslope hydrologic dynamics

Understanding connectivity between the soil and deeper bedrock groundwater is needed to accurately predict a watershed’s response to perturbation, such as drought. Yet, the bedrock groundwater dynamics in mountainous environments are typically under-constrained and excluded from watershed hydrologic models. Here, we investigate the role of groundwater characterized with decadal and longer water ages on the hydrologic and mass-transport processes within a steep snow-dominated mountain hillslope in the Central Rocky Mountains (USA). We quantify subsurface and surface water mass-balance, groundwater flowpaths, and age distributions using the ParFlow-CLM integrated hydrologic and EcoSLIM particle tracking models, which are compared to hydrometric and environmental tracer observations. An ensemble of models with varied soil and hydrogeologic parameters reproduces observed groundwater levels and century-scale mean ages inferred from environmental tracers. The numerical models suggest soil water near the toe of the hillslope contains considerable (>60 % of the mass-flux) contributions from bedrock flowpaths characterized with water ages >10 years. Flowpath connectivity between the deeper bedrock and soil systems is present throughout the year, highlighting the potentially critical role of groundwater with old ages on processes such as evapotranspiration and streamflow generation. The coupled numerical model and groundwater age observations show the bedrock groundwater system influences the hillslope hydrodynamics and should be considered in mountain watershed conceptual and numerical models.

Spatio-temporal variability in the strength, directionality, and relative importance of climate on occupancy and population densities in a philopatric mammal, the American pika (Ochotona princeps)

Species distribution models (SDMs) have been widely employed to evaluate species–environment relationships. However, when extrapolated over broad spatial scales or through time, these models decline in their predictive ability due to variation in how species respond to their environment. Many models assume species–environment relationships remain constant over space and time, hindering their ability to accurately forecast distributions. Therefore, there is growing recognition that models could be improved by accounting for spatio-temporal nonstationarity – a phenomenon wherein the factors governing ecological processes change over space or time. Here, we investigated nonstationarity in American pika (Ochotona princeps) relationships with climatic variables in the Rocky Mountains (USA). We first compared broad-scale differences in pika–climate patterns for occupancy and population density across the Southern, Central, and Northern Rockies. Next, we investigated within-ecoregion variation across four mountain ranges nested within the Northern Rockies. Lastly, we tested whether species–climate relationships changed over time within the Central Rockies ecoregion. Across all analyses, we found varying levels of nonstationarity among the climate metrics for both occupancy and density. Although we found general congruence in temperature metrics, which consistently had negative coefficients, and moisture metrics (e.g., relative humidity), which had positive coefficients, nonstationarity was greatest for summer and winter precipitation over both space and time. These results suggest that interpretations from one ecoregion should not be applied to other regions universally – especially when using precipitation metrics. The within-ecoregion analysis found much greater variation in the strength-of-relationship coefficients among the four mountain ranges, relative to the inter-regional analysis, possibly attributable to smaller sample sizes per mountain range. Lastly, the importance of several variables shifted through time from significant to insignificant in the temporal analysis. Our results collectively reveal the overall complexity underlying species–environment relationships. With rapidly shifting conditions globally, this work adds to the growing body of literature highlighting how issues of spatio-temporal nonstationarity can limit the accuracy, transferability, and reliability of models and that interpretations will likely be most robust at local to regional scales. Diagnosing, describing, and incorporating nonstationarity of species–climate relationships into models over space and time could serve as a pivotal step in creating more informative models.

Revised Paleozoic depositional history of the central Rocky Mountains (Utah and Colorado)

Precise sedimentological, stratigraphic, paleontological, and geochronological data collected from Paleozoic strata of the Dinosaur National Monument (DNM) area (NW Colorado and NE Utah) allow for comprehensive revision of the depositional history of that part of the central Rocky Mountains.Recovery of multiple species of the trilobite genus Elrathiella from sandstone beds in the middle of the Lodore Formation assigns those deposits to the mid-Miaolingian Ehmaniella Zone near the top of the Wuliuan Stage. This is significantly older than the previous “Dresbachian” age estimate for those coarse clastics, which attributed them to deposition during the late Miaolingian (latest Drumian or Guzhangian). This age revision re-positions the southernmost boundary of widespread Miaolingian inner detrital belt deposits of Wyoming to within 90 km of an extensive area of central Colorado where strata of this age are absent, and middle Furongian successions rest directly on basement. The boundary between these two regions, one with and one without Miaolingian strata, is nearly coincident with the Cheyenne belt, an east–west oriented Precambrian continental suture zone at the northern margin of the Yavapai Terrane. This association supports the idea that deep-seated crustal-scale features controlled the Cambrian paleotopography of the Rocky Mountain region and, in turn, the regional pattern of Cambrian transgression across western Laurentia.Early cursory paleontological work suggested a Devonian age for a thick sandstone interval near the top of the Lodore Formation, based on phosphatic fossils. We demonstrate that these fossils are in fact Cambrian obolid brachiopod shells. However, we provide multiple lines of evidence, including carbonate δ13C chemostratigraphic data, distinctive lithofacies, and stratigraphic relationships to argue that a thin interval of shale and dolostone, as well as a previously unrecognized paleokarst and regolith interval at the top of what was mapped as Lodore Formation, are in fact part of the Upper Devonian Parting Formation. The thick sub-Mississippian paleoregolith is consistent with elevated rates of weathering during the Late Devonian–Early Mississippian. δ13C chemostratigraphic data for the Madison Limestone include a large double-peaked Kinderhookian positive isotopic excursion (up to ~6.5 ‰), providing a precise estimate of the timing of Mississippian transgression in this part of the Rocky Mountain region.Detrital zircon geochronologic data for Cambrian to Pennsylvanian strata show remarkably consistent patterns dominated by ~1100 Ma, ~1400 Ma, and ~1700 Ma peaks, reflecting relative igneous quiescence over much of the Paleozoic for this region, a span of ~200 m.y., despite some orogenic activity (e.g., Antler Orogeny, Ancestral Rockies) during that time interval.

Revision of Quedius sensu stricto (Coleoptera: Staphylinidae)

We here present the first integrative revision of the subgenus Quedius Stephens, 1829 sensu stricto where taxonomic decisions are based on morphology, genomic phylogeny (published elsewhere) and single locus DNA evidence. The subgenus is restricted to the Holarctic region and includes some of the largest, most robust members of the genus Quedius. For species delimitation, a total of 200 COI barcodes covering nearly all species within the subgenus were evaluated through phylogenetic, cluster and network analysis. Taxonomic, distributional and bionomic data, all hitherto published and new are synthesized and an identification key is constructed for all species. All 20 species of Quedius s. str. are divided into five species groups based on genomic phylogeny, morphology, distributional patterns and practical considerations. Overall, there was good congruence among various lines of evidence. As exceptions, high COI barcode variability was found within the wingless and patchily distributed Q. unicolor Kiesenwetter, 1847 and Q. sundukovi Smetana, 2003 (3 and 5 BOLD BINs, respectively) from the Q. molochinus-group without corresponding morphological or geographic patterns. On the contrary, in the Q. pallipes-group very little divergence in the COI barcode was found between clearly morphologically separated species. From the taxonomically challenging Nearctic Quedius molochinoides-group, Quedius altanai Hansen & Brunke sp. nov. is described as new species from the central and southern Rockies, rendering Q. lanei Hatch, 1957 to be restricted to the eastern foothills of the Cascades, Sierra Nevada and Blue Mountains. In the case of Q. subunicolor and Q. altaicus, continuous morphological and COI variation firmly established the earlier suspected synonymy Quedius subunicolor Korge, 1961 = Quedius altaicus Korge, 1962 syn. nov. Other new synonyms established here are: Quedius pallipes Lucas, 1849 = Quedius simplicifrons Fairmaire, 1861 syn. nov. = Quedius levasseuri Coiffait, 1964 syn. nov.; Quedius hispanicus Bernhauer, 1898 stat. reinstituted = Quedius cobosi Coiffait, 1964 syn. nov.; Quedius fuliginosus (Gravenhorst, 1802) = Quedius latus Hochhuth, 1851 syn. nov. = Quedius viduus Sawada, 1965, syn. nov. Quedius gracilis Stephens, 1832 syn. rev. is moved from synonymy with Q. fuliginosus and placed into synonymy with Q. curtipennis Bernhauer, 1908, the younger being the valid name due to prevailing usage in accordance with the ICZN Article 23.9; Quedius hammianus Sharp, 1911 syn. revid., Q. secundus Last, 1952 syn. revid., and Q. rufulus Blümml, 1898 syn. revid., are moved from synonymy with Q. simplicifrons and placed into synonymy with Q. hispanicus Bernhauer, 1898; Quedius sardous Gridelli, 1924 syn. revid., and Q. leonhardi Bernhauer, 1914 syn. revid., are moved from synonymy with Q. molochinus (Gravenhorst, 1806) to synonymy with Q. pallipes. Human mediated dispersals, most likely through the historical transport of ship ballast, are noted as regular phenomenon for some members of the subgenus. Quedius fuliginosus, Q. curtipennis and Q. molochinus, introduced from the Palearctic to the Nearctic, are the most noticeable examples.

Shooting for abundance: Comparing integrated multi‐sampling models for camera trap and hair trap data

AbstractAbundance estimation is a vital goal in wildlife monitoring. Camera‐traps are a tool to survey wildlife populations noninvasively and can be used for abundance estimation if individuals are identifiable. However, for species without individual identification characteristics, camera‐trap surveys have often been combined with some other survey method such as capture‐recapture (CR, using traditional tags or DNA through hair snags or scat) to inform an integrated model. We discuss and apply two integrated models involving presence‐absence data from camera traps and CR data from hair traps to compare bias and precision to estimate the population density of grizzly bears of the central Rocky Mountains of Alberta, Canada. Unlike many other studies, we found that integrating presence‐absence data with CR data does not improve the precision of the density estimates. The possible reasons for such results are discussed in detail.

Ecology of the diatom Aulacoseira pusilla in oligotrophic mountain lakes, with implications for paleoclimate reconstructions

ABSTRACT Diatoms in lake sediments are used in paleoclimate reconstructions, particularly in treeless areas such as arctic and alpine regions. Some diatom species in the Aulacoseira group are often thought to bloom as lakes turnover (i.e., mix), suggesting links between these taxa and ice-out conditions. We investigated the distribution and ecology of Aulacoseira pusilla (Meister) Tuji & Houki 2004 in three high-elevation lakes of the U.S. Central Rocky Mountains. Vertical distributions of A. pusilla were quantified every three to four days shortly after the ice-out period for three weeks during July 2017. Populations from two of the lakes were incubated in situ in two experiments to assess the effects of Incubation depth × Nutrient additions and to quantify responses to light. In stratified conditions, the vertical distributions of this species varied spatially and temporally across the three lakes during the study period. There were blooms in the epilimnion of a moderately transparent lake and in deeper waters of a clear lake. Our results suggest that water transparency and its effects on light availability are important when defining relationships between this species and lake thermal conditions. Enhanced understanding of the ecology of A. pusilla will strengthen paleoclimate reconstructions using this species.

A Bryological Survey in Dickinson Park, Wind River Range, Wyoming

Dickinson Park is a difficult-to-access remote subalpine parkland in the Shoshone National Forest of Wyoming; it is located on the east slope of the Wind River Range (Central Rocky Mountains), immediately south of the Wind River Indian Reservation. The area has never been previously visited by bryologists. As a result of a bryological inventory conducted in the Park in 2012 (and subsequent laboratory research through 2019), 121 species, three subspecies, and five varieties were documented by voucher specimens. Of this total, 17 species, three subspecies, and two varieties are hepatics and 104 species and three varieties are mosses. The bryophyte checklist is presented, based on 990 specimens from 35 sites, collected by the author. Fourteen species of mosses have not previously been reported for Wyoming in the Flora of North America North of Mexico. There are 89 taxa (10 species, two subspecies, and one variety of hepatics and 74 species and two varieties of mosses) that are reported new for Fremont County. Three regionally rare species are documented on intact habitat sites of eutrophic fens located within the Park, Meesia triquetra, Paludella squarrosa, and Sphagnum angustifolium; their distribution in Wyoming is updated, based on recent publications and new herbarium materials.

Driving Utah's Rivers: Working Water in the West

Driving Utah's Rivers: Working Water in the West

BRYOFLORA OF THE SHOSHONE NATIONAL FOREST, WYOMING. PART 1. A CATALOGUE OF MOSSES AND LIVERWORTS OF THE BEARTOOTH PLATEAU AREA

This work is the first in a series of catalogues on the bryophytes of the oldest National Forest of the USA, the Shoshone National Forest. Bordering Yellowstone National Park and being a part of the Greater Yellowstone System, the Forest has retained a wide spectrum of its pristine representative areas, which support a unique bryophyte flora. Based on over 4600 specimens, the catalogue of the bryophytes of the Wyoming's Beartooth Plateau, the northernmost territories of the Forest, has been produced. This bryoflora is composed of 282 species (45 liverworts and 237 mosses) in the study area, representing approximately 53% of the Wyoming bryophyte flora. The richness of the flora is due to the high diversity of habitats, caused by the geological history of this portion of the Central Rocky Mountains, location of the study area essentially in the subalpine and alpine belts, climatic and hydrologic features, and low anthropogenic disturbance. The high elevations and associated habitat conditions allow for many disjunct arctic-alpine species (approximately 25% in the bryophyte flora). Remarkable extensions of upper elevation limits for 72 taxa are registered. Fifteen species, two subspecies, and two varieties of liverworts, as well as 56 species and eight varieties of mosses have not previously been reported for Wyoming in Flora of North America and Synopsis of Liverwort Flora of North America North of Mexico. Thirty-nine taxa (five species of liverworts and 32 species and two varieties of mosses) are of potential conservation concern in Wyoming, including two rare species with Pacific coastal affinities, Philonotis yezoana Besch. & Cardot and Sphagnum miyabeanum Warnst., and one species of extreme northern habitats, Sciuro-hypnum glaciale (Schimp.) Ignatov & Huttunen, being a novelty for continental North America. Brachythecium erythrorrhizon Schimp. var. alpinum Kosovich-Anderson & Ignatov was recently described, using material collected as part of this study.

The influence of forest fire aerosol and air temperature on glacier albedo, western North America

Over the past decade, western North America glaciers experienced strong mass loss. Regional mass loss during the ablation season is influenced by air temperature, but the importance of other factors such as changes in surface albedo remains uncertain. We examine changes in surface albedo for 17 glaciated regions of western North America as documented in a 20-year record (2000 to 2019) of MODIS daily snow albedo (MOD10A1). Trend analysis reveals that albedo declined for 4% to 81% of the albedo grid cells, and the largest negative trends were situated south of 60°N and in the provinces of British Columbia and Alberta. Sen's slope estimates indicate that 15 of 17 regions showed a decline of which the majority of the largest declines occurred within 100 m of glacier median elevation, suggesting that these declines are driven by a rise of the transient snowline. For most regions, albedo correlates strongly to temperature, and albedo trend in the Chugach region of Alaska, the South Coast, Southern Interior and Central and Southern Rockies of Canada show a significant relationship to aerosols optical depth. Temperature is approximately 2–6 times more predictive of the variation in albedo than AOD for the majority of regions, except the Southern Interior and Southern Rockies where albedo shows a greater dependence on AOD. Investigation of broadband albedo (MCD43A3) for snow grid cells above glacier median elevation in the Central and Southern Rockies shows that declines in the visible and near infrared portions of the spectrum are linked to the presence of forest fire generated aerosols. The results of this study indicate that glacier surface mass balance experiences a regional dependence on forest fire generated light absorbing particles.

Resolving the Cenozoic History of Rock Exhumation Along the Central Rocky Mountain Trench Using Apatite Low‐Temperature Thermochronology

AbstractThe Rocky Mountain Trench (RMT) extends through the Canadian Cordillera from the Yukon to northwest Montana. The RMT's impressive length and continuous nature have been interpreted to be the result of faulting, and localized erosion, along a continent‐scale zone of crustal weakness located beneath the RMT, possibly associated with the ancient continental margin. Despite the continuous nature of the RMT, its kinematics vary along strike from dextral strike‐slip faults in the north to normal faults in the south. The central RMT is thought to be the transition between these two structural zones. We use low‐temperature thermochronology to compare the cooling histories across the central RMT in eastern British Columbia. We report apatite fission track ages from 23 samples and apatite (U‐Th)/He ages from 25 samples along with thermal‐history models. Our results reveal three phases of rapid cooling that followed the Cretaceous‐Paleocene cordilleran thrusting in the Eocene, the early–mid Miocene, and from the late Miocene to recent. We find that the Malton Gneiss Complex exhumed as a horst structure 20–10 Ma bounded by the North Thompson Albreda Fault and the RMT. Normal faulting along the NTAF continued in the late Miocene as well as west side down normal faulting along the RMT. Our data suggest that extends along the southern RMT continued northward to at least this portion of the central RMT in multiple episodes during the Cenozoic. We suggest transtension occurred in our study area that was driven by orogenic collapse and lithospheric mantle delamination.

Evaluating Long-Term Seedling Growth Across Densities Using Nelder Plots and the Forest Vegetation Simulator (FVS) in the Black Hills, South Dakota, USA

Abstract Small-tree development affects future stand dynamics and dictates many ecological processes within a site. Accurately representing this critical component of stand development is important for evaluating treatment alternatives from fuel hazard reduction to harvest scheduling. As with all forest growth, competition with other vegetation is known to regulate small-tree growth dynamics. This study uses three Nelder plots with 45 years of ponderosa pine growth to understand competition effects on seedling growth and evaluate the Forest Vegetation Simulator (FVS) Central Rockies (CR) variant’s ability to represent these dynamics. Removal of herbaceous competition before planting increased tree diameters by 50–135% and height by 35–75% across a planting density gradient at age 12. However, by age 45, the effect of herbaceous competition on tree size was no longer evident. Instead, trees at the lowest planting density had diameters 2.5–3 times larger than the most densely grown trees. Forest Vegetation Simulator (FVS) simulations underpredicted diameter at breast height (dbh) by 35–50% and 0–35% for 12 and 45-year-old trees, respectively. There was an underprediction bias of 15–20% for heights at age 12 and overpredictions of 5–10% at age 45. Continuous underprediction of dbh will affect the reliability of modeled fuel treatment longevity and sustainable harvest scheduling.

Diversification, Introgression, and Rampant Cytonuclear Discordance in Rocky Mountains Chipmunks (Sciuridae: Tamias).

Evidence from natural systems suggests that hybridization between animal species is more common than traditionally thought, but the overall contribution of introgression to standing genetic variation within species remains unclear for most animal systems. Here, we use targeted exon capture to sequence thousands of nuclear loci and complete mitochondrial genomes from closely related chipmunk species in the Tamias quadrivittatus group that are distributed across the Great Basin and the central and southern Rocky Mountains of North America. This recent radiation includes six overlapping, ecologically distinct species (Tamias canipes, Tamias cinereicollis, Tamias dorsalis, T. quadrivittatus, Tamias rufus, and Tamias umbrinus) that show evidence for widespread introgression across species boundaries. Such evidence has historically been derived from a handful of markers, typically focused on mitochondrial loci, to describe patterns of introgression; consequently, the extent of introgression of nuclear genes is less well characterized. We conducted a series of phylogenomic and species-tree analyses to resolve the phylogeny of six species in this group. In addition, we performed several population-genomic analyses to characterize nuclear genomes and infer coancestry among individuals. Furthermore, we used emerging quartets-based approaches to simultaneously infer the species tree (SVDquartets) and identify introgression (HyDe). We found that, in spite of rampant introgression of mitochondrial genomes between some species pairs (and sometimes involving up to three species), there appears to be little to no evidence for nuclear introgression. These findings mirror other genomic results where complete mitochondrial capture has occurred between chipmunk species in the absence of appreciable nuclear gene flow. The underlying causes of recurrent massive cytonuclear discordance remain unresolved in this group but mitochondrial DNA appears highly misleading of population histories as a whole. Collectively, it appears that chipmunk species boundaries are largely impermeable to nuclear gene flow and that hybridization, while pervasive with respect to mtDNA, has likely played a relatively minor role in the evolutionary history of this group. [Cytonuclear discordance; hyridization; introgression, phylogenomics; SVDquartets; Tamias.].

Botrychium furculatum (Ophioglossaceae), a New Moonwort Species from the Rocky Mountains of North America

Botrychium furculatum S. J. Popovich & Farrar is a new species widespread in the central and southern Rocky Mountains from Alberta and Montana south to New Mexico, with additional populations in the Cypress Hills of Saskatchewan and the Black Hills of Wyoming and South Dakota. Based on allozyme banding patterns, it is inferred to be an allotetraploid with B. pallidum W. H. Wagner as one parent and another, as yet undescribed, diploid species (B. “farrarii”) as the other parent. Genetically, B. furculatum is distinguished from B. pallidum by exhibiting fixed heterozygous loci in which expressed alleles of one of the genomic contributions matches those of B. pallidum, whereas many alleles of the other genomic contribution have not been detected in B. pallidum, but are displayed by B. “farrarii.” Morphologically, a suite of leaf characters differentiates B. furculatum from B. pallidum, particularly a more pronounced bowed or wishbone-like junction of sporophore and trophophore. Gradations in morphology and color between the two species have led to erroneous reports of B. pallidum in the Rocky Mountains. A key to differentiate B. furculatum from similar species is presented.

A model evaluation framework applied to the Forest Vegetation Simulator (FVS) in Colorado and Wyoming lodgepole pine forests

The Forest Vegetation Simulator (FVS) growth and yield model is widely used throughout the United States, but recent studies have reported unexpectedly large bias for some regional model variants. Here we propose a general framework for model evaluation, designed to highlight model strengths and weaknesses and inform calibration efforts. We apply the framework to evaluate the Lodgepole Pine (LP) model of the FVS Central Rockies Variant (FVS-CR), which has rarely been evaluated in the literature despite its widespread use in the western US. We started with a qualitative verification of the structure and logic of the FVS-CR LP model against a modified Bakuzis matrix, determining that it adequately reproduces known patterns of stand dynamics. We then compared stand-level growth simulations to a chronosequence developed from 554 Forest Inventory and Analysis (FIA) plots measured in Colorado and Wyoming lodgepole pine forests. This quantitative validation exercise revealed that the default model settings substantially over-predict basal area and total stand carbon after 50 years for both pure lodgepole pine stands and mixed lodgepole pine stands containing a minor proportion of Engelmann spruce, subalpine fir, and quaking aspen. Using equivalence testing to validate the large-tree diameter increment model against a separate dataset of 3,790 remeasured trees on 124 lodgepole pine FIA plots, we found that the default FVS–CR LP model adequately predicts lodgepole diameter growth, though we observed large variation in model errors. Equivalence tests also revealed systematic under-estimation of spruce–fir and over-estimation of aspen productivity. Finally, we conducted a sensitivity analysis to identify the most important model parameters and data inputs driving simulated stand structure and carbon accumulation in both the short- (50 years) and long-term (200 years). The model shows the greatest sensitivity to initial species composition; a small proportion of aspen, spruce, or fir seedlings led to long-term stand re-structuring and greatly increased carbon accumulation. Other sensitive parameters included site index, the fixed large-tree diameter increment adjustment factor, and the parameter controlling the point at which density-dependent self-thinning begins (maximum stand density index). This evaluation leads us to conclude that the FVS-CR LP model tends to under-estimate tree mortality (particularly in young stands) and the default site index represents relatively high productivity stands, such that re-calibration may often be necessary to capture realistic long-term stand behaviors. Our sensitivity analysis provides guidance for future efforts to re-calibrate the FVS-CR LP model and highlights the importance of collecting site index and seedling species composition data wherever possible to produce the most realistic simulations.

Late Paleogene emergence of a North American loess plateau

Abstract The relative roles of tectonics and global climate in forming the hydroclimate for widespread eolian deposition remain controversial. Oligocene loess has been previously documented in the interior of western United States, but its spatiotemporal pattern and causes remain undetermined. Through new stratigraphic record documentation and data compilation, we reveal the time transgressive occurrence of loess beginning in the latest Eocene in the central Rocky Mountains, that expands eastward to the Great Plains across the Eocene-Oligocene transition (EOT). Our climate simulations show that moderate uplift of the southern North America Cordillera initiated drying in the Cordilleran hinterland and immediate foreland, forming a potential dust source and sink, and global cooling at the EOT expanded the drying and eolian deposition eastward by causing retreat of the North American Monsoon. Therefore, the eolian deposition reflects continental aridification induced both by regional tectonism and global climate change during the late Paleogene.

Weed-Suppressive Bacteria Fail to Control Bromus tectorum Under Field Conditions

The exotic winter annual grass Bromus tectorum L. (downy brome or cheatgrass) infests millions of hectares of western rangelands. Weed-suppressive bacteria (ACK55 and D7 strains of Pseudomonas fluorescens Migula 1895) have been shown to reduce B. tectorum populations in eastern Washington. Unfortunately, outside of Washington, little is known about the efficacy of these or other weed-suppressive bacteria. We used Petri-plate and plant-soil bioassays to test effects of ACK55 and D7 on B. tectorum from Montana and Wyoming. We also tested effects of ACK55 on B. tectorum at six field sites in Montana and one in Wyoming. P. fluorescens reduced B. tectorum germination and root and shoot lengths in Petri-plates but had no effect on plants during growth chamber plant-soil bioassays or field experiments. Bromus arvensis L. (field brome or Japanese brome), a species similar to B. tectorum, was prevalent at two of our sites, and ACK55 was ineffective against B. arvensis as well. Our findings contribute to a growing body of evidence that the ACK55 and D7 strains of P. fluorescens are not reliable tools for controlling B. tectorum in the Northern Great Plains, Central Rocky Mountains, and elsewhere.