North-central Wyoming Research Articles

New material of Lophiparamys debequensis from the Willwood Formation (early Eocene) of Wyoming, including the first postcrania of the genus

Abstract We report new material of the rare early Eocene rodent Lophiparamys debequensis Wood, 1962 from the Willwood Formation of the southern Bighorn Basin, north-central Wyoming. The new material constitutes the first record of L. debequensis from the Bighorn Basin and documents aspects of the anatomy of Lophiparamys that were previously unknown, including a portion of the maxilla and a portion of the tarsus. The maxillary fragment demonstrates that Lophiparamys has a small P3 and a relatively large infraorbital canal. The tarsus of Lophiparamys is similar to that of other early rodents but differs in a few features that suggest an arboreal locomotor repertoire, including an asymmetric astragalar trochlea, long astragalar neck, transverse astragalar sustentacular facet, short calcaneal tuber, elongate calcaneal ectal facet, and circular calcaneal cuboid facet. The presence of arboreally adapted features in the tarsus of Lophiparamys is consistent with a hypothesized relationship between small-bodied Eocene microparamyine rodents and extant Gliridae. Phylogenetic analysis fails to consistently support this relationship or monophyly of Microparamyinae, but both remain plausible. Comparison of L. debequensis with other species of the genus emphasizes the distinctiveness of L. debequensis and suggests the presence of multiple lineages of Lophiparamys.

The influence of initial phenolic content and UV-screening effectiveness on abiotic photodegradation of Wyoming big sagebrush litter collected along an elevation gradient

Photodegradation of plant litter exposed to solar radiation appears to be important for carbon cycling in arid ecosystems. We measured how initial concentrations of ultraviolet (UV)-absorbing phenolics and epidermal UV-transmittance influenced abiotic photodecomposition of Artemisia tridentata ssp. Wyomingensis (Wyoming big sagebrush) leaves exposed to ultraviolet radiation in a laboratory setting. These leaves were collected from standing vegetation along a 1053-m elevation gradient in North-central Wyoming that represented a natural ecocline in UV-screening effectiveness in sagebrush. After 310 d, sagebrush litter lost 6.0–9.4% of its initial mass and abiotic decomposition rates were linear, rather than exponential. Initial concentrations of both UV-A and UV-B absorbing phenolics were strong predictors for litter mass remaining, with coefficients of determination (r2) values being −0.70 and −0.62, respectively. It appears that foliar biochemistry and epidermal UV-screening effectiveness may influence photodegradation by reducing UV flux into interior portions of plant litter.

Laramide crustal detachment in the Rockies: Cordilleran shortening of fluid-weakened foreland crust

ABSTRACTWhat causes previously stable continental crust in the forelands of Cordilleran orogenic systems to shorten during low-angle subduction? The National Science Foundation/EarthScope Bighorn Project combined seismic imaging of the crust and Moho with kinematic modeling of Laramide (Late Cretaceous–Paleogene) basement-involved deformation to address this question. In north-central Wyoming, asymmetrical ENE-verging upper-crustal folds are highly discordant with broader, N-trending warps in the Moho, indicating crustal detachment. Restorable cross sections of ENE-directed detachment at a depth of ~30 km, combined a smaller component of NNW–SSE shortening due to the east-narrowing shape of the crustal allochthon, can explain the anastomosing network of Laramide basement-cored arches without major deformation of the underlying mantle lithosphere.Thrust-related fold geometries and west-to-east initiation of deformation in the Laramide and Sevier thrust belts point to Cordilleran end-loading from the west. Differences between Laramide (~N65E) and plate (~N25E) convergence directions, along with the fanning of Laramide shortening directions from nearly E–W to the south to NE–SW to the north, indicate slip partitioning during end-loading west of the Rockies.Sub-horizontal detachment with a near-zero critical taper within cratonic crust suggests an extremely weak Laramide detachment zone during deformation. Analogous lower-crustal deformation in subduction forearcs is associated with slow earthquakes and slab dehydration. We hypothesize that low-angle subduction of the Farallon Plate suppressed fluid-consuming melting and corner-flow processes that characterize higher-angle subduction. This allowed subduction-generated fluids to escape upward into the overlying continental lithosphere, causing retrograde metamorphism and increased fluid pressure that facilitated crustal detachment. This hydration-based hypothesis predicts that crustal detachment will accompany major earthquakes in active analog orogens.

Reworked pollen reduces apparent floral change during the Paleocene-Eocene Thermal Maximum

Abstract Plant megafossils from the Paleocene-Eocene Thermal Maximum (PETM) in the Bighorn Basin, north-central Wyoming, USA, document a dramatic shift in floral composition, whereas palynofloral change from the same sections has appeared to be more subtle. We investigated this discrepancy by quantifying pollen preservation and measuring the stable carbon isotope composition of specific pollen taxa. Pollen grains belonging to two common latest Paleocene taxa are poorly preserved in PETM samples, and their δ13Cpollen is similar during the latest Paleocene and PETM. In contrast, pollen grains of a thermophilic taxon that became more abundant during the PETM are pristine, and the δ13Cpollen of PETM specimens is ∼4‰ lower than that of latest Paleocene specimens. More broadly, pollen grains belonging to lineages currently centered in temperate climates are poorly preserved when found in PETM samples, whereas in the same samples, pollen belonging to lineages now centered in the tropics are well preserved. These differences in preservation and isotopic composition indicate extensive redeposition of older pollen grains during the PETM. Increased abundance of Cretaceous palynotaxa in PETM samples confirms erosion and redeposition, likely resulting from more episodic and intense precipitation. Exclusion of reworked palynotaxa from analyses reveals that, as in the megaflora, temperate taxa were absent during the PETM at the time when dry tropical taxa briefly appeared. Major climate changes like the PETM may commonly destabilize landscapes, increase reworking, and thus smooth patterns of change in microfloras, leading to underestimates of the rate and magnitude of floral response to past global change.

Luminescence ages and new interpretations of the timing and deposition of Quaternary sediments at Natural Trap Cave, Wyoming

Natural Trap Cave, located in the Big Horn Mountains of north-central Wyoming, has a history of trapping and preserving a range of North American fauna that plummeted into the deep vertical entrance. These animal remains were buried and preserved within sediments of the main chamber and, in turn, have helped elucidate the procession of faunal dynamics during the latest glacial cycle. The cave location, south of the Laurentide and Cordilleran Ice Sheets, and proximal to Yellowstone, is at an ideal geographical juncture to provide insights to ecological changes in North America. The sediments that the animals are buried in inform us about transport and deposition both inside and outside of the cave that relate to catchment dynamics. We report on a series of optically stimulated luminescence (OSL) ages derived from samples obtained within the cave during excavation work in 2014 and in 2018. We also examine chronology produced by argon, tephrochronology, fission track, and luminescence techniques that have been used for understanding the infilling of the cave. The cave sediment ages and in situ measured gamma spectroscopy as measured in this study helped resolve an improved chronological age model when combined with previous data.The suite of OSL ages is interpreted through the stratigraphic relationships (and vertebrates contained within) which requires the use of an adequate age model; we use either the central age model or minimum age model where appropriate and with justification. Lowest sediments are dated to ∼150 ka with a hiatus at ∼130 to 52 ka. Above this, sediment deposition and entrainment of paleontological materials are representative of Pleistocene and early Holocene times, between 37 ± 6 ka and 7.6 ± 0.5 ka. The stratigraphic architecture suggests that deposition of materials into the cave is episodic and rapid, followed by quiescent periods where hydrologic scour, heavy overland flow, or possibly a cryo-hydrologic process may have altered unit relationships. Thus, the complementary geochronometers and the characteristics of quartz versus feldspar luminescence signals improve temporal interpretations of these complex deposits. This adapted understanding of mixing also sets the stage for future work with the aim to improve our understanding of ages and sources for ash units within these cave deposits. The three ash units recognized in the cave may represent an in-situ reworking of the same ash or may be representative of previously undocumented eruptions from the Yellowstone Caldera.

An age-depth model and revised stratigraphy of vertebrate-bearing units in Natural Trap Cave, Wyoming

Excavations at Natural Trap Cave (NTC) began in the mid-1970's and quickly yielded evidence of a diverse steppe fauna that existed during the Last Glacial Maximum (MIS 2) along the western slope of the Bighorn Mountains in north central Wyoming. NTC is a karst pit cave with a 24.5 m vertical drop into a roughly 43 m wide bell-shaped ‘Main Chamber’ and during the course of early excavations a plugged entrance to a fossil-bearing ‘Lower Chamber’ was discovered. Stratigraphic relationships below the entrance to the Main Chamber of the cave were originally studied in the mid-1970's, but were never formally published. Although stratigraphy, taphonomy, and depositional circumstances were briefly discussed over the following years, little has been done to correlate the numerous stratigraphic schemes used by various authors. In this study, four stratigraphic sections were measured and analyzed to establish an easily modifiable lithostratigraphic system of nomenclature. We provide the first correlations of all stratigraphic nomenclature used throughout excavations at NTC to facilitate comparisons with current and previous collections and publications. By leveraging more than 100 radioisotopic dates we developed an age-depth model and chronostratigraphic framework to further interrogate spatiotemporal relationships between strata, paleoenvironmental proxies, and fossil assemblages. Deposition is shown to be discontinuous; sediment accumulation in the study area is restricted to the buildup through peak penultimate and Last Glacial maxima. More recent (<10 ka) Holocene deposits unconformably cover the eroded surface of underlying Pleistocene strata. There is active reworking of sediments with transport and deposition of reactivated material within the Lower Chamber. We note that the two hiatuses coincide with interglacial periods and may reflect changing depositional circumstances within the cave such as extended periods of non-deposition, erosion, or bypass (possibly leading to deposition in the Lower Chamber). Contrary to previous reports, we demonstrate that it is unlikely a prominent snow cone existed or contributed to the pattern of sediment and fossil distribution within the study area, furthermore, we do not observe a continuous Pleistocene-Holocene transition in the study area. Further stratigraphic work will be needed to better understand the interrelationship between Main and Lower chamber deposits and the evolution of sediment accumulation in NTC.

Paleo-vegetation and environmental history of Natural Trap Cave based on pollen and carbon isotope analyses

Pollen and carbon isotope data from Natural Trap Cave provides insights into the environmental conditions of the Bighorn Basin, in north-central Wyoming, USA during the time intervals 151.1 to 132.2 cal ka BP, 51.8 to 17.4 cal ka BP, and 10.4 cal ka BP to present. Similarities between the buildup of the penultimate and last glacial maxima include abundant Artemisia, Amaranthaceae, Asteraceae, and Poaceae pollen, which, when combined with high δ13C values (>−25.0‰) and low plant discrimination values (18.0–19.0‰) from sedimentary organic matter, indicate steppe-like, cold-dry conditions. Between 151 and 142.5 cal ka BP, abundant Poaceae associated with much lower δ13C values (−28.0‰ to −26.0‰) and higher plant discrimination values (19.0‰–21.0‰) could be indicative of relatively wet summers. Similarly, after 25 cal ka BP increases in Poaceae may indicate wet conditions during the growing season. Holocene conditions differ from the earlier sections of the record, with greater arboreal pollen abundance (i.e., Pinus), consistent with woodland expansion in the region. Carbon isotope data from sedimentary organic matter show the Holocene was more humid than the glacial conditions of the late Pleistocene. This is especially clear at the start of the Holocene when a large negative carbon isotope excursion (CIE, < −28.0‰) occurred, providing a distinct chemostratigraphic marker defining the Pleistocene-Holocene boundary within these cave sediments. The association of this CIE with a pronounced spike in Pinus pollen supports an interpretation of a short-lived interval (<1000 years) of extremely warm, wet, forested conditions at this site.

Modeling Rangeland Grasshopper (Orthoptera: Acrididae) Population Density Using a Landscape-Level Predictive Mapping Approach.

Since the mid-19th century, grasshoppers have posed a substantial threat to North American rangelands as well as adjacent croplands and have the potential to cost the economy millions of dollars in annual damages. The United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) have gone to great lengths to ensure that rangeland grasshopper populations remain below an economic impact threshold across the western United States. However, current grasshopper forecasting efforts by the USDA are based solely on the previous year's grasshopper density and do not take region-specific environmental factors (e.g., climate and topography) into account. To better understand the effects of climate and landscape heterogeneity on rangeland grasshopper populations, we assessed the relationship between grasshopper density survey data from across 56 sites between 2007 and 2017 for four counties in north central Wyoming with 72 biologically relevant geographic information system (GIS)-based environmental variables. A regression model was developed to predict mean adult grasshopper density from 2012 to 2016, which was then used to forecast grasshopper density in 2017. The best-fit predictive model selected using Akaike's Information Criterion (AICc) explained 34.5% of the variation in mean grasshopper density from 2012 to 2016. October precipitation and past mean grasshopper density from 2007 to 2011 were among the best predictors of mean grasshopper density in 2012-2016. Our results also suggest that rangelands in central Sheridan County, southwest Johnson County, and southeast Washakie County are more prone to grasshopper outbreaks. Most importantly, this study demonstrated that both biotic and abiotic environmental variables influence grasshopper density and should be considered in future forecasting efforts.

Monitoring long-term riparian vegetation trends to inform local habitat management in a mountainous environment

Riparian ecosystems provide critical habitat for many species, yet assessment of vegetation condition at local scales is difficult to measure when considering large areas over long time periods. We present a framework to map and monitor two deciduous cover types, upland and riparian, occupying a small fraction of an expansive, mountainous landscape in north-central Wyoming. Initially, we developed broad-scale predictions of predominant woody vegetation types by integrating Landsat data into species distribution models and combining subsequent outputs into a synthesis map. Then, we evaluated a 35-year Landsat time series (1985–2019) using the Mann-Kendall test to identify significant trends in the condition of upland and riparian deciduous vegetation and assessed the rate and direction of change using the Theil-Sen estimator. Finally, we used plot level data to assess the utility of the framework to detect bottom-up controls (ungulate browse pressure and management actions) on vegetation condition. The synthesis map had an overall correct classification rate of 87% and field data indicated deciduous vegetation within 45 m of coniferous forest faces increased pressure of conifer expansion. The trend assessment identified consistent patterns operating at the landscape scale across both upland and riparian deciduous vegetation; a predominant greening trend was observed for 12 years followed by a 9-year browning trend, before switching back to a greening trend for the last 13 years of the study. Our results indicate trends are driven by the climate of the measurement period at the landscape scale. Although we did not find conclusive evidence to establish a strong link between browse pressure and satellite data, we highlight examples where prevailing trends can be overridden by local disturbance or management intervention. This framework is transferable to other understudied riparian environments throughout western North America to provide insight on ecohydrological processes and assess global and local stressors across broad spatiotemporal scales.

Does the Owl Creek fault zone of north-central Wyoming extend to the Black Hills of South Dakota? Implications for basement architecture of the Wyoming Province

The North Owl Creek fault is an E–W-striking, basement-rooted Laramide structure located in the Owl Creek Mountains of north-central Wyoming that likely has Precambrian origins. It is defined by a rectilinear zone of deformation that extends eastward into the subsurface where it is postulated to intersect the Kaycee fault zone of the western Powder River Basin, and perhaps extends into western South Dakota along the Dewey fault zone. Several localized basement-rooted wrench zones have been identified in the foreland of the North American Cordillera; however, identification of more regional zones has been minimal. The presence of larger fault zones that cut nearly the entire Archean basement across the Wyoming Province has implications for Precambrian plate tectonics and structural inheritance in foreland basins such as the Powder River. This paper presents results of a structural analysis that tests this hypothesis.

Effect of terrain, environment and infrastructure on potential CO2 pipeline corridors: a case study from North-Central USA

In this paper, a study has been undertaken with the objective to delineate the potential CO2 pipeline corridors through the north-central region of the USA including North Dakota, Montana, Wyoming, Utah and Colorado to enable the implementation of carbon capture storage and utilization projects. A combination of GIS along with analytical hierarchy process is used to identify regions with high potential for pipeline development. A total of 19 thematic information layers have been utilized to map the study area which reflect the effect of ecology, environment and existent infrastructure towards laying new CO2 pipeline networks. Weights are assigned to each class in the thematic maps based on their characteristics, capacity of building and maintaining pipelines and the potential environmental risk of CO2 pipelines from the literature. A tract suitability index is developed which identified Western North Dakota, central Wyoming and Western Montana as regions highly suitable for development of CO2 pipelines. The study reveals that 54.5% of the region of interest is suitable for pipeline construction while 15.39% of land is classified as either poor or infeasible candidate for locating CO2 pipelines. It is also revealed that pipeline right-of-way, water bodies and population centres have the most significant impact on future pipeline development. The results of the study are also varied to show the effect different factors could have on the potential CO2 corridors and are then correlated with existent pipeline in study area to check the validity of the resulting analysis.

An additional example of the ichnogenus Zoophycos in Cambrian strata (Gallatin Formation; Wyoming, USA)

The ichnogenus Zoophycos is relatively rare in Cambrian-age sedimentary rocks, being far more commonly encountered in post-Devonian, and particularly post-Paleozoic, strata. A new occurrence of Zoophycos from the Upper Cambrian Gallatin Formation of the Bighorn Mountains, north-central Wyoming, USA, is reported herein. Material consists of a single specimen preserved within quartz silt representing the upper surface of a graded quartz arenite bed. The burrow is a relatively wide, curved, horizontally oriented lobe with a poorly visible marginal tube but well-developed internal lamellae. Discovery of this specimen contributes to the paleobiogeographic distribution of lower Paleozoic Zoophycos, adds to the literature suggesting that most Cambrian Zoophycos were horizontal and shallow-tier structures, and provides further support to the notion that relatively complex deposit-feeding behavior evolved earlier in the Phanerozoic than had long been recognized.

Geochronology of the southern margin of the Bighorn Batholith, Wyoming

The Bighorn Mountains in north-central Wyoming reveal one of the largest exposures of 2800 Ma to 3000 Ma rocks in Laurentia. The northern part of the crystalline core is composed of the composite Bighorn batholith, whereas the central and southern areas of the range expose older gneiss complexes as well as minor supracrustal rocks. We provide new high-resolution LA-ICPMS U-Pb data on zircons sampled from eleven samples of tonalite, granodiorite, mylonite, and migmatite from the southern margin of the Bighorn batholith in the headwaters of the north fork of Paint Rock Creek. These rocks range from strongly foliated to massive and are difficult to subdivide into mappable units in the field because of their lithologic and structural similarities. Several cross-cutting mylonite zones (&lt;10-meter-wide) that trend ~N70°E-N80E and dip steeply are present in the study area. Three distinct age populations are evident: ~2930-2940 Ma, 2905-2915 Ma, and 2880-2890 Ma. Several samples contain xenocrystic zircons &gt;3000 Ma, ranging to 3500 Ma, which indicates assimilation of older crust. Each of the three age populations reported here are older than the previously reported age of ~2850 Ma age for the northern Bighorn Batholith but within the 2890 Ma, 2940 Ma, and 2950 Ma age groupings previously reported for the southern gneiss terrane. Three conclusions can be drawn from these data. First, the Bighorn batholith, at least along the southern margin, contains phases at least 80 million years older than the northern phase of the body, and emplacement was protracted and occurred over a ~100 Ma period. Second, episodes of both intrusion and shearing took place in this area as the various phases of the Bighorn batholith were emplaced. Finally, the existence of inherited zircons within the Bighorn batholith in the age range of ~3.0 Ga to 3.5 Ga indicates that the Bighorn batholith intruded through older crust. This older crust is perhaps a northern extension of Sacawee block in the northern Granite Mountains of central Wyoming, which may underlie the Bighorn Mountains.

Genetic diversity and population structure in Cary’s Beardtongue Penstemon caryi (Plantaginaceae), a rare plant endemic to the eastern Rocky Mountains of Wyoming and Montana

Penstemon caryi is a narrow-range endemic angiosperm found primarily on sparsely vegetated limestone outcrops in the Bighorn and Pryor Mountains of north-central Wyoming and south-central Montana. A former candidate for listing under the Endangered Species Act, and currently a species of concern in these states, P. caryi is potentially threatened by habitat loss due to encroaching anthropogenic activities, such as limestone quarrying and road construction. In an effort to assess the capacity of P. caryi to withstand habitat loss and degradation, we used simple sequence repeats (SSRs) and amplified fragment length polymorphism (AFLP) markers to examine genetic diversity and differentiation of P. caryi populations from the Pryor Mountains of Montana and the southern Bighorn Mountains of Wyoming. Our analyses revealed overall moderate to high levels of genetic diversity in P. caryi, but with relatively lower levels of diversity in populations from the Pryor Mountains. There are fewer known individuals of Penstemon caryi in Montana, and because the examined populations from Montana exhibited less genetic diversity than those from Wyoming, populations from Montana may face an increased risk of population decline and extirpation. Both the AFLP and SSR data sets found population structure between different regions (Montana vs. Wyoming), while AFLP markers identified further subdivision between Wyoming populations. Despite moderate to high levels of genetic diversity, P. caryi is still a species at risk due to impending environmental stresses such as global climate change and human encroachment, which may be especially troublesome given its narrow distribution and the specificity of its habitat preferences.

Paleoecological implications of the first prehistoric record of water vole (Microtus richardsoni) from Washington state, USA

AbstractRemains of the North American water vole (Microtus richardsoni) have previously been recovered from late Pleistocene and Holocene deposits in southwestern Alberta, western Montana, and north-central Wyoming. All are within the historically documented modern range of the metapopulation occupying the Rocky Mountains; no ancient remains of this large microtine have previously been reported from the metapopulation occupying the Cascade Range. Four lower first molar specimens from the late Holocene Stemilt Creek Village archaeological site in central Washington here identified as water vole are from the eastern slope of the Cascade Range and are extralimital to the metapopulation found in those mountains. There is no taphonomic evidence indicating long-distance transport of the teeth, and modern trapping records suggest the local absence of water voles from the site area today is not a function of sampling error. The precise age of the Stemilt Creek Village water voles is obscure but climate change producing well-documented late Holocene advances of nearby alpine glaciers could have created habitat conditions conducive to the apparent modest shift in the range of the species represented by the remains.

Patterns in stream greenhouse gas dynamics from mountains to plains in northcentral Wyoming

AbstractQuantification of small stream contributions to global carbon cycling is key to understanding how freshwater systems transmit and transform carbon between terrestrial and atmospheric pools. To date, greenhouse gas emissions of carbon dioxide and methane from freshwaters, particularly in mountainous regions, remain poorly characterized due to a lack of direct field observations. Using a unique longitudinal approach, we conducted field surveys across two ecoregions (Middle Rockies and Great Plains) in the Clear Creek watershed, a subwatershed of Wyoming's Powder River Basin. We took direct measurements of stream gases using headspace sampling at 30 sites (8 June to 23 October). We observed the lowest and most variable concentrations in headwaters, which flow through a federally designated alpine wilderness area. By contrast, the Great Plains exhibited 1.45 and 4 times higher pCO2 and pCH4 concentrations and the relative contributions of methane increased downstream. Fluxes during snowmelt were 45% and 58% higher for CO2 and CH4 than during base flow but overall were lower than estimates for other systems. Variability for pCO2 was highest during late summer and in the uppermost sections of the headwaters. The high heterogeneity and common undersaturation observed through space and time, especially in the mountains, suggest that downscaled regional estimates may fail to capture variability in fluxes observed at these smaller scales. Based on these results, we strongly recommend higher resolution time series studies and increased scrutiny of systems at near equilibrium, inclusive of winter storage and ice‐off events, to improve our understanding of the effects of seasonal dynamics on these processes.

Does Wyoming's Core Area Policy Protect Winter Habitats for Greater Sage-Grouse?

Conservation reserves established to protect important habitat for wildlife species are used world-wide as a wildlife conservation measure. Effective reserves must adequately protect year-round habitats to maintain wildlife populations. Wyoming's Sage-Grouse Core Area policy was established to protect breeding habitats for greater sage-grouse (Centrocercus urophasianus). Protecting only one important seasonal habitat could result in loss or degradation of other important habitats and potential declines in local populations. The purpose of our study was to identify the timing of winter habitat use, the extent which individuals breeding in Core Areas used winter habitats, and develop resource selection functions to assess effectiveness of Core Areas in conserving sage-grouse winter habitats in portions of 5 Core Areas in central and north-central Wyoming during winters 2011-2015. We found that use of winter habitats occured over a longer period than current Core Area winter timing stipulations and a substantial amount of winter habitat outside of Core Areas was used by individuals that bred in Core Areas, particularly in smaller Core Areas. Resource selection functions for each study area indicated that sage-grouse were selecting habitats in response to landscapes dominated by big sagebrush and flatter topography similar to other research on sage-grouse winter habitat selection. The substantial portion of sage-grouse locations and predicted probability of selection during winter outside small Core Areas illustrate that winter requirements for sage-grouse are not adequately met by existing Core Areas. Consequently, further considerations for identifying and managing important winter sage-grouse habitats under Wyoming's Core Area Policy are warranted.

Drying and Shade Effects on Spearmint Oil Yields and Composition

‘Native’ spearmint (Mentha spicata L.) is one of the two most widely grown spearmints in the United States and in other countries. Recent studies demonstrated the feasibility of growing ‘Native’ spearmint as a cash crop for north–central Wyoming. Transportation and energy costs of commercial mint production can be reduced by drying the spearmint in windrows in the field for a few days after harvest and before oil extraction. This method of drying mint has been a common practice in the traditional mint production regions of the world. However, there is a knowledge gap regarding the effect of this drying method on the yield and composition of ‘Native’ spearmint oil. Field and laboratory experiments were conducted in Wyoming to evaluate the effects of drying duration in days after harvest (DAH: 0, 1, 2, 3, 4, 7, or 11) and drying conditions (shade and sun) on the yield of essential oil (EO) and on the concentrations of different oil constituents (beta-pinene, myrcene, limonene, eucalyptol, cis-sabinene hydrate, 4-terpineol, cis-dihydro carvone, cis-carveol, carvone, iso-dihydro carveol acetate, beta-bourbonene, beta-caryophyllene, alpha-humulene/transbeta-farnesene, and germacrene D). Neither drying duration nor drying condition had a significant effect on oil yield. The average yield of essential oil was 0.25 g of oil per 100 g of fresh weight. Drying duration and drying conditions had a significant effect on the composition of EOs. The concentrations of myrcene and germacrene-D were higher in the EOs from plants dried under shade (3.2% and 2.4%, respectively) than the EOs from plants dried under direct sun (3% and 2.2%, respectively). The concentration of beta-pinene was higher in plants dried under direct sun than under shade (0.92% vs. 0.88%). Carvone ranged from 51% to 53% in the oil and was higher in EOs from plants dried for 1 and 2 DAH and lower in EOs from plants dried for 7 days. Drying of ‘Native’ spearmint under direct sun in Wyoming for up to 11 DAH can be used as an effective tool to reduce transportation and energy costs without affecting oil yields.

Wyoming big sagebrush screens ultraviolet radiation more effectively at higher elevations

The flux of biologically-effective ultraviolet radiation (UV) is diminished by atmospheric absorption which may cause physiological and morphological phenotypic differences among plant populations at different elevations. We examined UV-screening effectiveness of leaves of Artemisia tridentata ssp wyomingensis (Wyoming big sagebrush) along an 800-m elevation gradient in North-central Wyoming with a pulse-amplitude modulated fluorometer. Adaxial epidermal transmittance of UV increased at lower elevations; means ranged from 2.3% (high elevation) to 10.2% (low elevation). To provide a proximate explanation for this relationship, we collected leaves across the gradient and estimated concentrations of bulk-soluble UV-absorbing compounds (λ = 300 and 365 nm) and the density of trichomes on the adaxial surface. Concentrations of UV-absorbing compounds decreased with elevation and ranged from 0.64–2.25 A300 cm−2 and 0.43–1.35 A365 cm−2. Trichome density increased from 14,400 cm−2 at low elevation to 22,500 cm−2 at high elevation. Because the distance along the elevation gradient was only 18 km, gene flow likely prevents ecotypic differentiation; the ultimate cause of the ecocline in screening effectiveness is likely the evolution of environmentally-induced phenotypic plasticity in both biochemical and anatomical properties of leaves in response to variation in UV irradiance.

An aboveground–belowground assessment of ecosystem properties associated with exotic annual brome invasion

Exotic annual brome invasion has been well studied in western North American rangelands, particularly for Bromus tectorum L. invasion in sagebrush (Artemisia tridentata) grasslands. We examined both aboveground and belowground properties in native sagebrush grassland and adjacent areas dominated by exotic annual bromes (B. tectorum L. and Bromus japonicus Thunb.) to better understand the fundamental ecological differences between native and invaded areas. Field sites were located in north central Wyoming, USA, and plots were established in areas that had been historically subject to wildfire and either (1) recolonized by native sagebrush grassland vegetation or (2) invaded by exotic annual bromes. We employed measures of vegetation community structure as well as soil physical, chemical, and microbiological properties. Plots with greater than 20 % exotic annual brome cover had significantly less cover of all native vegetation functional groups resulting in lower richness and evenness than native plots. Invaded plots also had low diversity plant communities that were continuous and uniform across space. Soils beneath invaded plant communities had higher infiltration rates, higher levels of total nitrogen, and a lower C/N ratio than the native soils. Invaded soils also had 90–96 % lower abundance of all soil microbial groups measured by phospholipid fatty acid. We conclude that areas dominated by exotic annual bromes display different aboveground and belowground properties compared to the native community, and these changes possibly include spatial and temporal shifts in soil resources and organic matter processing.