Northern Great Basin Research Articles

Holocene fire occurrence and alluvial responses at the leading edge of pinyon–juniper migration in the Northern Great Basin, USA

Fire and vegetation records at the City of Rocks National Reserve (CIRO), south-central Idaho, display the interaction of changing climate, fire and vegetation along the migrating front of single-leaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma). Radiocarbon dating of alluvial charcoal reconstructed local fire occurrence and geomorphic response, and fossil woodrat (Neotoma) middens revealed pinyon and juniper arrivals. Fire peaks occurred ~10,700–9500, 7200–6700, 2400–2000, 850–700, and 550–400calyrBP, whereas ~9500–7200, 6700–4700 and ~1500–1000calyrBP are fire-free. Wetter climates and denser vegetation fueled episodic fires and debris flows during the early and late Holocene, whereas drier climates and reduced vegetation caused frequent sheetflooding during the mid-Holocene. Increased fires during the wetter and more variable late Holocene suggest variable climate and adequate fuels augment fires at CIRO. Utah juniper and single-leaf pinyon colonized CIRO by 3800 and 2800calyrBP, respectively, though pinyon did not expand broadly until ~700calyrBP. Increased fire-related deposition coincided with regional droughts and pinyon infilling ~850–700 and 550–400calyrBP. Early and late Holocene vegetation change probably played a major role in accelerated fire activity, which may be sustained into the future due to pinyon–juniper densification and cheatgrass invasion.

Implications of New Radiocarbon Ages on Coiled Basketry from the Northern Great Basin

AbstractCoiled basketry dates to more than 8,000 years ago in the Eastern Great Basin and is found in the Western Basin by 4,500 years ago. In the Northern Great Basin, archaeological basketry is dominated by twineware; fewer than 20 fragments of coiled basketry have been reported. Coiling has long been thought to have appeared very late in the Northern Basin, and the perceived late presence of coiling in the north has been considered by some to be an indicator of a late Numic incursion from the south. Recent direct radiocarbon dating of fiber samples from the coiled specimens from the Northern Great Basin undermines the previous assumptions of a uniformly late age. Though rare, coiling has a consistent presence in the region for more than 2,500 years. Further, its distribution suggests that this technological influence may have derived primarily from eastern, rather than southern, sources.

Variation in Timing of Planting Influences Bluebunch Wheatgrass Demography in an Arid System

Establishing perennial grasses from seed in postdisturbance Wyoming big sagebrush (Artemesia tridentata subsp. wyomingensis Welsh) communities is often unsuccessful, due in part to a lack of knowledge of the seedling ecology of perennial grasses. We examined the influence of planting timing on germination and seedling demography of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) in the northern Great Basin. In 2008 (year 1) and 2009 (year 2) we planted seeds monthly, September–December, in 1-m2 plots (500 seeds per plot) using a randomized block design with five replications. Germination timing was indexed using seed bags placed adjacent to 1-m2 plots and retrieved at 2-wk intervals in fall and 1-mo intervals in spring. Seedlings were marked in March–June of the year following planting; seedlings alive in July were considered initially established. Planting in September and October had up to 80% germination prior to winter, whereas December plantings germinated mainly in spring and at reduced rates (15–35%). Seeds planted in September and October emerged approximately a month earlier than November–December plantings. The percentage of germinated seeds that emerged was highest for September–October plantings but the percentage of emergent seeds surviving to the end of the first growing season was highest for later plantings. Final seedling density was lowest for November planting in year 1 and highest for September and October planting in year 2. Our data indicate that timing of and performance at critical stages of seedling development were affected by planting month. We suggest that it may be possible to use emerging technologies (e.g., seed coatings or germplasm manipulations) to produce variable chronologies of seedling development with single plantings and allow managers to exploit multiple temporal windows of opportunity for seedling establishment.

Predicting nesting habitat of Northern Goshawks in mixed aspen-lodgepole pine forests in a high-elevation shrub-steppe dominated landscape

We developed a habitat suitability model for predicting nest locations of breeding Northern Goshawks (Accipiter gentilis) in the high-elevation mixed forest and shrub-steppe habitat of south-central Idaho, USA. We used elevation, slope, aspect, ruggedness, distance-to-water, canopy cover, and individual bands of Landsat imagery as predictors for known nest locations with logistic regression. We found goshawks prefer to nest in gently-sloping, east-facing, non-rugged areas of dense aspen and lodgepole pine forests with low reflectance in green (0.53 - 0.61 μm) wavelengths during the breeding season. We used the model results to classify our 43,169 hectare study area into nesting suitability categories: well suited (8.8%), marginally suited (5.1%), and poorly suited (86.1%). We evaluated our model’s performance by comparing the modeled results to a set of GPS locations of known nests (n = 15) that were not used to develop the model. Observed nest locations matched model results 93.3% of the time for well suited habitat and fell within poorly suited areas only 6.7% of the time. Our method improves on goshawk nesting models developed previously by others and may be applicable for surveying goshawks in adjacent mountain ranges across the northern Great Basin.

Distribution of Low-Elevation American Pika Populations in the Northern Great Basin

Abstract The recent discovery that a portion of the historically described populations of American pikas Ochotona princeps in the Great Basin of North America appear to be extinct added emphasis to earlier warnings that these populations may be highly vulnerable, in particular those occurring at low elevations (<2,500 m). Pikas in the Great Basin have received increased scientific interest; however, there is still little known about the distribution or number of populations throughout their range. Here we report on the discovery of several previously undescribed low-elevation pika populations in Southeast Oregon and Northwest Nevada. The average elevation of sites currently occupied by pikas was 1,993 m (range = 1,648–2,357 m). This and other recent discoveries suggest that pikas may be more common at low elevations in portions of the northern Great Basin than previously suspected (i.e., >2,500 m).

Insights from a synthesis of old and new climate-proxy data from the Pyramid and Winnemucca lake basins for the period 48 to 11.5 cal ka

A synthesis of old and new paleoclimatic data from the Pyramid and Winnemucca lake basins indicates that, between 48.0 and 11.5·103 calibrated years BP (hereafter ka), the climate of the western Great Basin was, to a degree, linked with the climate of the North Atlantic. Paleomagnetic secular variation (PSV) records from Pyramid Lake core PLC08-1 were tied to the GISP2 ice-core record via PSV matches to North Atlantic sediment cores whose isotopic and(or) carbonate records could be linked to the GISP2 δ18O record. Relatively dry intervals in the western Great Basin were associated with cold Heinrich events and relatively wet intervals were associated with warm Dansgaard-Oeschger (DO) oscillations. The association of western Great Basin dry events with North Atlantic cold events (and vice versa) switched sometime after the Laurentide Ice Sheet (LIS) reached its maximum extent. For example, the Lahontan highstand, which culminated at 15.5 ka, and a period of elevated lake level between 13.1 and 11.7 ka were associated with cold North Atlantic conditions, the latter period with the Youngest Dryas event. Relatively dry periods were associated with the Bølling and Allerød warm events. A large percentage of the LIS may have been lost to the North Atlantic during Heinrich events 1 and 2 and may have resulted in the repositioning of the Polar Jet Stream over North America. The Trego Hot Springs, Wono, Carson Sink, and Marble Bluff tephras found in core PLC08-1 have been assigned GISP2 calendar ages of respectively, 29.9, 33.7, 34.1, and 43.2 ka. Given its unique trace-element chemistry, the Carson Sink Bed is the same as Wilson Creek Ash 15 in the Mono Lake Basin. This implies that the Mono Lake magnetic excursion occurred at approximately 34 ka and it is not the Laschamp magnetic excursion.The entrance of the First Americans into the northern Great Basin is dated to approximately 14.4 ka, a time when the climate was relatively dry. Evidence for human occupation of the Great Basin is lacking for the next 1100 years (y); i.e., the oldest western stemmed point site in the Great Basin dates to 13.3 ka. Two hypotheses are suggested for this cultural hiatus: (1) the climate had deteriorated to the point that people vacated the Great Basin, or (2) people moved to basin-bottom wetlands that persisted during the dry period, and then the subsequent Younger Dryas wet event erased the archaeological evidence deposited around the low-elevation wetland sites.

A new interpretation of deformation rates in the Snake River Plain and adjacent basin and range regions based on GPS measurements

We evaluate horizontal Global Positioning System (GPS) velocities together with geologic, volcanic, and seismic data to interpret extension, shear, and contraction within the Snake River Plain and the Northern Basin and Range Province, U.S.A. We estimate horizontal surface velocities using GPS data collected at 385 sites from 1994 to 2009 and present an updated velocity field within the Stable North American Reference Frame (SNARF). Our results show an ENE-oriented extensional strain rate of 5.9 {+-} 0.7 x 10{sup -9} yr{sup -1} in the Centennial Tectonic belt and an E-oriented extensional strain rate of 6.2 {+-} 0.3 x 10{sup -9} yr{sup -1} in the Intermountain Seismic belt combined with the northern Great Basin. These extensional strain rates contrast with the regional north-south contraction of -2.6 {+-} 1.1 x 10{sup -9} yr{sup -1} calculated in the Snake River Plain and Owyhee-Oregon Plateau over a 125 x 650 km region. Tests that include dike-opening reveal that rapid extension by dike intrusion in volcanic rift zones does not occur in the Snake River Plain at present. This slow internal deformation in the Snake River Plain is in contrast to the rapidly-extending adjacent Basin and Range provinces and implies shear along boundaries of the Snakemore » River Plain. We estimate right-lateral shear with slip rates of 0.5-1.5 mm/yr along the northwestern boundary adjacent to the Centennial Tectonic belt and left-lateral oblique extension with slip rates of 10{sup 6} yrs, the low-strain field in the Snake River Plain and Owyhee-Oregon Plateau would extend through the Quaternary.« less

Cascade Points in the Northern Great Basin: A Radiocarbon-Dated Foliate Point Assemblage from Warner Valley, Oregon

Although common in the northern Great Basin, foliate points sometimes referred to as Cascade points are generally regarded as poor temporal markers because they are found in early, middle, and even late Holocene contexts. It is unclear whether this broad timespan is a function of prolonged use of the point form, later groups recycling discarded artifacts, or a combination of both. We review the spatial and temporal distribution of foliate points in the northern Great Basin and present new data derived from work at a stratified rockshelter in Oregon's Warner Valley. There, we have uncovered foliate projectile points that meet the original definition and more recent refinements of the Cascade point type associated with a late early Holocene and middle Holocene occupation. We present technological and source provenance data for the points and the associated lithic assemblage and reconstruct how prehistoric foragers used the rockshelter.

Multiyear Home-Range Ecology of Common Side-blotched Lizards in Eastern Oregon with Additional Analysis of Geographic Variation in Home-range Size

We studied the spatial ecology of Common Side-blotched Lizards (Uta stansburiana) in the northern Great Basin desert of eastern Oregon. Over 3 yr (2007–2009) we collected 3675 coordinates from 51 males and 60 females during the breeding season (mid-May to early July). We found significant variation among years and between the sexes in home-range size, but contrasting evidence for a relationship between body size and home-range size. Lizard home ranges overlapped those of other lizards extensively and the number of overlapping home ranges within and between the sexes as well as the percentage of unique home range varied among study years. However, we found no evidence that lizards are minimizing their overlaps with the same sex and maximizing their overlaps with the opposite sex. By studying home ranges over multiple years we found that lizards exhibit strong year-to-year fidelity in home-range location, which may be a consequence of relatively high interannual survival. We also present long-term data on the home ranges of Common Side-blotched Lizards from a population in central California that were studied for 8 (females) or 10 (males) consecutive yr as well as new analyses of Tinkle's (1967a,b) 6-yr dataset from west Texas. We found that winter rainfall, population density, and lizard sex were significant predictors of home-range size across years within both sites, though the effects of density and sex appear to be more robust than rainfall. By combining data on home-range ecology from nine study populations of Uta stansburiana, we tested for the effects of latitude of origin, rainfall, population density, and lizard sex on home-range size across the geographic distribution of this species. Similar to our results within sites, rainfall, density, and sex have significant effects on home-range size when comparing sites, but again the effects of density and sex appear to be more robust than rainfall. Latitude of origin also appears to explain variation in home-range size independent of ecosystem productivity (i.e., rainfall, density). Thus, we conclude that ecosystem productivity is an important determinant of density and spatial ecology of lizard populations and that even modest fluctuations in productivity may influence population density and home-range ecology, but that latitude of origin remains important independent of these factors.

Turnover in burrowing rodents: The roles of competition and habitat change

Changes in the burrowing herbivore fauna during the Cenozoic have led to the suggestion that competitive replacement was a driving force in the ecology and evolution of the burrowing herbivore guild. Alternatively, it has been proposed that differences in habitat preferences were associated with the expansion and contraction of the ranges of burrowing herbivores. We examine hypotheses of drivers of mammalian evolution in this guild by looking for evidence of apparent competitive replacements at a regional scale in the middle to late Miocene fossil record of the northern Great Basin. Mylagaulids are most common from 17.5 to 9 Ma, in the Hemingfordian through Clarendonian North American Land Mammal Ages and decline to extinction in the Hemphillian (9 to 5 Ma), at which time the family Geomyidae became more common in this region. In addition to observing this turnover within the guild, we find that geomyids and mylagaulids may occupy different habitats as indicated by evidence from mammalian assemblages and paleopedology. This suggests that mylagaulids and geomyids, rather than competing, may be tracking the extent of their preferred environment. We find no evidence for direct biotic interaction between the members of the guild and suggest instead that the changing abundance of mylagaulids and geomyids in Oregon's Miocene was shaped by habitat partitioning.

Prey Body Size and Ranking in Zooarchaeology: Theory, Empirical Evidence, and Applications from the Northern Great Basin

The use of body size as an index of prey rank in zooarchaeology has fostered a widely applied approach to understanding variability in foraging efficiency. This approach has, however, been critiqued—most recently by the suggestion that large prey have high probabilities of failed pursuits. Here, we clarify the logic and history of using body size as a measure of prey rank and summarize empirical data on the body size-return rate relationship. With few exceptions, these data document strong positive relationships between prey size and return rate. We then illustrate, with studies from the Great Basin, the utility of body size-based abundance indices (e.g., the Artiodactyl Index) when used as one component of multidimensional analyses of prehistoric diet breadth. We use foraging theory to derive predictions about Holocene variability in diet breadth and test those predictions using the Artiodactyl Index and over a dozen other archaeological indices. The results indicate close fits between the predictions and the data and thus support the use of body size-based abundance indices as measures of foraging efficiency. These conclusions have implications for reconstructions of Holocene trends in large game hunting in western North America and for zooarchaeological applications of foraging theory in general.

The Peyote road: religious freedom and the Native American Church

Despite challenges by the federal government to restrict the use of peyote, the Native American Church, which uses the hallucinogenic cactus as a religious sacrament, has become the largest indigenous denomination among American Indians today. The Peyote Road examines the history of the NAC, including its legal struggles to defend the controversial use of peyote.Thomas C. Maroukis has conducted extensive interviews with NAC members and leaders to craft an authoritative account of the church's history, diverse religious practices, and significant people. His book integrates a narrative history of the Peyote faith with analysis of its religious beliefs and practices - as well as its art and music - and an emphasis on the views of NAC members. Deftly blending oral histories and legal research, Maroukis traces the religion's history from its Mesoamerican roots to the legal incorporation of the NAC; its expansion to the northern plains, Great Basin, and Southwest; and challenges to Peyotism by state and federal governments, including the Supreme Court decision in Oregon v. Smith. He also introduces readers to the inner workings of the NAC with descriptions of its organizational structure and the Cross Fire and Half Moon services. The Peyote Road updates Omer Stewart's classic 1987 study of the Peyote religion by taking into consideration recent events and scholarship. In particular, Maroukis discusses not only the church's current legal issues but also the diminishing Peyote supply and controversies surrounding the definition of membership. Today approximately 300,000 American Indians are members of the Native American Church. The Peyote Road marks a significant case study of First Amendment rights and deepens our understanding of the struggles of NAC members to practice their faith.

Crustal structure beneath the High Lava Plains of eastern Oregon and surrounding regions from receiver function analysis

[1] We analyze teleseismic P-to-S receiver functions to image crustal structure beneath the High Lava Plains (HLP) of eastern Oregon and surrounding regions. Coverage from 206 broadband seismic stations provides the first opportunity to resolve variations in crustal composition, thickness, and heterogeneity on scales of a few km in depth and tens of km laterally across the HLP region. We utilize both H − κ stacking and a new Gaussian-weighted common conversion point stacking technique. We find crust that is ≥40 km thick beneath the Cascades, Idaho Batholith, and Owyhee Plateau and thinner (∼31 km) crust beneath the HLP and northern Great Basin. Low Poisson's ratios of ∼0.240 characterize the granitic crust beneath the Idaho Batholith, while the Owyhee Plateau exhibits values of ∼0.270, typical of average continental crust. The Owyhee Plateau is a thick simple crustal block with distinct edges at depth. The western HLP exhibits high average values of 0.304, typical for regions of widespread basaltic volcanism. Combined with other geological and geophysical observations, the areas of abnormally high Poisson's ratios (∼0.320) and low-velocity zones in the crust beneath north-central and southern Oregon are consistent with the presence of partial melt on either side of the HLP trend, suggesting a central zone where crustal melts have drained to the surface, perhaps enabled by the Brothers Fault Zone. Thicker crust and an anomalous N-S band of low Poisson's ratios (∼0.252) skirting the Steens Mountain escarpment is consistent with residuum from a midcrustal magma source of the massive flood basalts, supporting the view of extensive mafic underplating and intraplating of the crust from Cenozoic volcanism.

Influence of Elevation on Carbonate Contents in Stratified Soils, Northern Great Basin and Adjacent Mountains, U.S.A

Many soils in the western U.S.A. contain one or several carbonate-enriched zones (CEZ). Their carbonate admixture is often attributed to steady eolian influx, with intermittent leaching episodes of variable intensity leading to pedogenic enrichment at various depths. This hypothesis would require carbonate contents to decrease and depths to those horizons to increase with elevation. Here I compute correlations for the upper three CEZ of the surface soil and of up to two buried soils between elevation, carbonate content, depth to horizon, and particle-size distribution to test for elevation- dependent trends. Actually, carbonate-content decreases with elevation indicate such trends exist and can be determined with this approach. However, some significant relationship of elevation and depth to CEZ is not supported by the data. Furthermore, influence of local carbonate on CEZ in the surface soils calls for lateral translocation. Gravelly, now-buried sediments collected eolian carbonate better than finer ones, which finding implies these sediments were at the surface once and fossilized later. Altogether, the data indicate cyclical evolution: Several cycles of the formation of colluvial slope deposits with admixed carbonate-bearing loess particles were each followed by pedogenic translocation of the carbonate just to the depth of the next parent-material disconformity. Thus, disconformities are major triggers of soil-carbonate accumulation.

A New Variety of Lomatium ravenii (Apiaceae) from the Northern Great Basin and Adjacent Owyhee Region

Variability in the group of Lomatium species comprising L. nevadense, L. ravenii, and L. foeniculaceum has led to conflicting classification schemes. While some taxonomists have treated L. ravenii as a distinct species made up of all the populations from California, Nevada, Idaho, and Oregon, others considered L. ravenii to be nothing more than a morphological extreme of L. nevadense. We examined morphological and phylogenetic data from across the range of L. ravenii, concluding that variation in the species warrants varietal distinction. Non-metric multidimensional scaling analysis of 29 populations shows two distinct groups—one from the vicinity of Ravendale, California, and one from the rest of the range in California, Nevada, Oregon, and Idaho. Phylogenetic analysis of the ITS, rps16 intron, and cpDNA rpl32-trnLUAG genes from seven populations supports these two groups. We refer to the geographically widespread population as Lomatium ravenii var. paiutense and recommend reassessment of the conservation status of the more narrowly endemic Ravendale populations.

Phenotypic and Genetic Characterization of Western Prairie Clover Collections From the Western United States

Few North American legumes are available for rangeland revegetation in the semiarid western United States. Western prairie clover (Dalea ornata [Douglas ex Hook.] Eaton & J. Wright) is a perennial legume with desirable forage characteristics and is distributed in the northern Great Basin, Snake River Basin, and southern Columbia Plateau. Understanding the genetic and ecotypic variability of this species is a prerequisite for developing populations suitable for revegetation purposes. To address this need, we established two common-garden plots of western prairie clover from 22 sites in Idaho, Oregon, and Washington. Significant variation was detected among the collections for all traits measured. Among the measured traits, flowering date was correlated with collection-site temperature and elevation. Population structure estimates from 474 amplified-fragment length polymorphism markers resulted in two distinct, genetically differentiated groups and a third admixed group, and flowering date played a significant role in discriminating those genetic-based groupings of collections. Positive correlations were observed between phenotypic and genetic distance matrices (r = 0.33, P = 0.005), phenotypic and geographic distance matrices (r = 0.35, P = 0.002), and genetic and geographic distance matrices (r = 0.31, P = 0.009). Based on these results, we recommend that two germplasm sources of western prairie clover be developed for use across the collection area, one from the Deschutes River region and the other encompassing Idaho, Washington, and eastern Oregon collection sites.

Yield Responses of Ruderal Plants to Sucrose in Invasive‐Dominated Sagebrush Steppe of the Northern Great Basin

Restoration of sagebrush‐steppe plant communities dominated by the invasive ruderals Bromus tectorum (cheatgrass) and Taeniatherum caput‐medusae (medusahead) can be facilitated by adding carbon (C) to the soil, stimulating microbes to immobilize nitrogen (N) and limit inorganic N availability. Our objectives were to determine responses in (1) cheatgrass and medusahead biomass and seed production; (2) soil microbial biomass C and N; and (3) inorganic soil N to a range of C doses and to calculate the lowest dose that yielded a significant response. In November 2005, we applid 12 C doses ranging from 0 to 2,400 kg C/ha as sucrose to plots sown with cheatgrass and medusahead at two sites in the northern Great Basin. Other ruderal plants established in our plots, and this entire ruderal community was negatively affected by C addition. End‐of‐year biomass of the ruderal community decreased approximately by approximately 6% at each site for an increase in C dose of 100 kg C/ha. For the same increase in C, microbial biomass C increased by 2–4 mg/kg in November 2005 and March 2006, but not in July 2006. There was little, if any, microbial soil N uptake, as microbial biomass N increased by 0.3 mg/kg at only one site at the earliest date, in November 2005. Soil nitrate (NO3−) measured via resin capsules placed in situ for the study duration decreased at both sites with increasing C. Although we found no threshold dose of C, for a significant reduction in ruderal biomass, we calculated lowest significant doses of 240–640 kg C/ha.

Persistence of Western Juniper (Juniperus occidentalis) Resource Islands Following Canopy Removal

Western juniper (Juniperus occidentalis Hook.) encroachment has altered the spatial distribution of soil nutrients and plants in semi-arid systems of the northern Great Basin, forming nutrient enriched ‘resource islands’ under tree canopies. Our goal was to determine the persistence of resource island characteristics after restoration treatment (tree cutting). The study site was a privately owned grazing allotment in eastern Oregon where trees had been cut eight and fifteen years ago. In each age class and in uncut western juniper woodlands, juniper stumps or trees were randomly selected for sampling. At each bole three radial transects, set at 120° from each other, were marked and soil cores were collected to 5-cm depth at distances of 50, 100, 150 and 300-cm from the bole then combined to a single composite sample per distance class. Samples were analyzed for total C and N, soluble P, K, Ca, Fe, Al, Mg and Na and pH. Despite increases in shrub, forb and grass crops in the fifteen-year old cut treatment, western juniper resource island effects were still evident for most soil variables measured; tree island soils were significantly higher in Ctot, Ntot, P, K and Ca compared to inter-island soils. Resource island persistence was attributed to litter mats beneath relic canopies. Management efforts may be more successful at preventing establishment of undesired annuals by focusing on young juniper stands where resource islands are less developed.

Vegetation Characteristics of Mountain and Wyoming Big Sagebrush Plant Communities in the Northern Great Basin

Dominant plant species are often used as indicators of site potential in forest and rangelands. However, subspecies of dominant vegetation often indicate different site characteristics and, therefore, may be more useful indicators of plant community potential and provide more precise information for management. Big sagebrush (Artemisia tridentata Nutt.) occurs across large expanses of the western United States. Common subspecies of big sagebrush have considerable variation in the types of sites they occupy, but information that quantifies differences in their vegetation characteristics is lacking. Consequently, wildlife and land management guidelines frequently do not differentiate between subspecies of big sagebrush. To quantify vegetation characteristics between two common subspecies of big sagebrush, we sampled 106 intact big sagebrush plant communities. Half of the sampled plant communities were Wyoming big sagebrush (A. tridentata subsp. wyomingensis [Beetle & A. Young] S. L. Welsh) plant communities, and the other half were mountain big sagebrush (A. tridentata subsp. vaseyana [Rydb.] Beetle) plant communities. In general, mountain big sagebrush plant communities were more diverse and had greater vegetation cover, density, and biomass production than Wyoming big sagebrush plant communities. Sagebrush cover was, on average, 2.4-fold higher in mountain big sagebrush plant communities. Perennial forb density and cover were 3.8- and 5.6-fold greater in mountain compared to Wyoming big sagebrush plant communities. Total herbaceous biomass production was approximately twofold greater in mountain than Wyoming big sagebrush plant communities. The results of this study suggest that management guidelines for grazing, wildlife habitat, and other uses should recognize widespread subspecies as indicators of differences in site potentials. Las especies de plantas dominantes se usan frecuentemente como indicadores de potencial en sitios de bosques y pastizales. Sin embargo, las subespecies de vegetación dominante a menudo indican diferentes características y entonces, pueden ser indicadores más útiles del potencial de una comunidad de plantas, ya que dan información más precisa para su manejo. Big sagebrush (Artemisia tridentata Nutt.) se encuentra presente en grandes extensiones a través del oeste de Estados Unidos. Especies comunes de big sagebrush tienen considerables variaciones en cuanto al tipo de lugares en las que están presentes, sin embargo, es escasa la información que cuantifique estas diferencias en cuanto a sus características vegetativas. En consecuencia, las directrices para el manejo de fauna y de la tierra no hacen diferencia entre subespecies de big sagebrush. Para cuantificar las características vegetativas entre dos subespecies comunes de big sagebrush, obtuvimos muestras de 106 plantas de comunidades intactas de big sagebrush. La mitad de las plantas muestreadas se obtuvieron de comunidades de Wyoming big sagebrush (A. tridentata subsp. wyomingensis [Beetle & A. Young] S. L. Welsh) y la otra mitad se seleccionó de una comunidad de mountain big sagebrush (A. tridentata subsp. vaseyana [Rydb.] Beetle). La cobertura de Sagebrush fue 2.4 veces mayor en promedio en las comunidades de mountain big sagebrush. La densidad y cobertura de herbáceas perennes fue 3.8 y 5.6 veces mayor en mountain sagebrush comparada con las comunidades de Wyoming big sagebrush. La biomasa total producida por las herbáceas fue aproximadamente 2 veces mayor en comunidades de plantas de mountain big sagebrush que en las comunidades de Wyoming big sagebrush. Los resultados de este estudio sugieren que las directrices para el manejo de pastoreo, fauna y otros usos deben reconocer la amplia variabilidad de subespecies como indicadores en sitios con diferentes potenciales.

Life Cycle and Mesoscale Frontal Structure of an Intermountain Cyclone

AbstractHigh-resolution analyses and MesoWest surface observations are used to examine the life cycle and mesoscale frontal structure of the “Tax Day Storm,” an intermountain cyclone that produced the second lowest sea level pressure observed in Utah during the instrumented period and the strongest cold frontal passage at the Salt Lake City International Airport in the past 25 years. A key mesoscale surface feature contributing to the cyclone’s evolution is a confluence zone that extends downstream from the Sierra Nevada across the Great Basin. Strong contraction (i.e., deformation and convergence) within this Great Basin confluence zone (GBCZ) forms an airstream boundary that is initially nonfrontal but becomes the locus for surface frontogenesis as it collects and concentrates baroclinicity from the northern Great Basin, including that accompanying an approaching baroclinic trough. Evaporative and sublimational cooling from postfrontal precipitation, as well as cross-front contrasts in surface sensible heating, also play an important role, accounting for up to 40% of cross-front baroclinicity. As an upper-level cyclonic potential vorticity anomaly and quasigeostrophic forcing for ascent move over the Great Basin, cyclone development occurs along the GBCZ and developing cold front rather than within the Sierra Nevada lee trough, as might be inferred from classic models of lee cyclogenesis. Front–mountain interactions ultimately produce a very complex frontal evolution over the basin-and-range topography of northern Utah.The analysis further establishes the role of the GBCZ in intermountain frontogenesis and cyclone evolution. Recognition of this role is essential for improving the analysis and prediction of sensible weather changes produced by cold fronts and cyclones over the Intermountain West.