Eastern Rocky Mountains Research Articles

Environmental drivers behind the genetic differentiation in mountain chickadees (Poecile gambeli).

Anthropogenic climate change has a large impact on wildlife populations and the scale of the impacts has been increasing. In this study, we utilised 3dRAD sequence data to investigate genetic divergence and identify the environmental drivers of genetic differentiation between 12 populations of mountain chickadees, family Paridae, sampled across North America. To examine patterns of genetic variation across the range, we conducted a discriminant analysis of principal components (DAPC), admixture analysis, and calculated pairwise Fst values. The DAPC revealed four clusters: southern California, eastern Rocky Mountains, northwestern Rocky Mountains, and Oregon/northern California. We then used BayeScEnv to highlight significant outlier SNPs associated with the five environmental variables. We identified over 150 genes linked to outlier SNPs associated with more than 15 pathways, including stress response and circadian rhythm. We also found a strong signal of isolation by distance and local temperature was highly correlated with genetic distance. Maxent simulations showed a northward range shift over the next 50 years and a decrease in suitable habitat, highlighting the need for immediate conservation action.

Genetic data improves niche model discrimination and alters the direction and magnitude of climate change forecasts.

Ecological niche models (ENMs) have classically operated under the simplifying assumptions that there are no barriers to gene flow, species are genetically homogeneous (i.e., no population-specific local adaptation), and all individuals share the same niche. Yet, these assumptions are violated for most broadly distributed species. Here, we incorporate genetic data from the widespread riparian tree species narrowleaf cottonwood (Populus angustifolia) to examine whether including intraspecific genetic variation can alter model performance and predictions of climate change impacts. We found that (1) P.angustifolia is differentiated into six genetic groups across its range from México to Canada and (2) different populations occupy distinct climate niches representing unique ecotypes. Comparing model discriminatory power, (3) all genetically informed ecological niche models (gENMs) outperformed the standard species-level ENM (3-14% increase in AUC; 1-23% increase in pROC). Furthermore, (4) gENMs predicted large differences among ecotypes in both the direction and magnitude of responses to climate change and (5) revealed evidence of niche divergence, particularly for the Eastern Rocky Mountain ecotype. (6) Models also predicted progressively increasing fragmentation and decreasing overlap between ecotypes. Contact zones are often hotspots of diversity that are critical for supporting species' capacity to respond to present and future climate change, thus predicted reductions in connectivity among ecotypes is of conservation concern. We further examined the generality of our findings by comparing our model developed for a higher elevation Rocky Mountain species with a related desert riparian cottonwood, P.fremontii. Together our results suggest that incorporating intraspecific genetic information can improve model performance by addressing this important source of variance. gENMs bring an evolutionary perspective to niche modeling and provide a truly "adaptive management" approach to support conservation genetic management of species facing global change.

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.

The Importance of Conifers for Facilitation at Treeline: Comparing Biophysical Characteristics of Leeward Microsites in Whitebark Pine Communities

ABSTRACTIn many of the alpine-treeline ecotones (ATE) of the Rocky Mountains, Pinus albicaulis (whitebark pine) is the most common conifer initiating tree islands through facilitation. We examined whether microsites leeward of P. albicaulis experience more moderate microclimate, less sky exposure, and more total soil carbon and nitrogen than other common types of leeward microsites. From July to September 2010, 2011, and 2012, in two study areas on the eastern Rocky Mountain Front, we compared microclimate, sky exposure, and total soil carbon and nitrogen leeward of four common microsites, P. albicaulis, Picea engelmannii (Engelmann spruce), rock, and unprotected (exposed). Microsites leeward of P. albicaulis did not consistently experience the most moderate microclimate, but both P. albicaulis and P. engelmannii leeward microsites had lower daily photosynthetically active radiation (PAR), lower average wind speeds, lower soil temperature maxima, and higher soil temperature minima. In general, conifer microsites had significantly lower values for sky exposure; but, the performance of each microsite type varied from micro to study-area scales. Our results highlight the importance of conifers as nurse objects for facilitating treeline community development in the ATE, and especially P. albicaulis because of its high abundance. High losses of P. albicaulis from infection by Cronartium ribicola may alter community dynamics and treeline response to climate warming.

In this issue of Weather

We begin our February 2016 issue of Weather with a study of the dangers of winds over mountain ranges on p. 27. In ‘Wind hazard in the alpine zone: a case study in Alberta, Canada’ Chris Hugenholtz and Geoffrey Van Heller discuss the effects of winds of a relatively extreme mountain environment using data from an automatic weather station in the Front Ranges of the eastern Rocky Mountains. Dangers may include the buffeting and chilling effects of the wind itself, the melting of snow due to adiabatic warming and the formation of intense areas of low pressure in the lee of the mountains. Economic losses may be significant, and there is a clear need for all to be aware of the effects of strong winds over mountains.On p. 32, the next paper is an interesting study of high‐resolution wind and temperature data recorded at Great Dun Fell on the high ground of the Pennines. Martin Young's article ‘Rapid temperature and wind fluctuations at a mountain site in northern England on 9/10 February 2015’ describes fascinating changes close to the level of a marked temperature inversion at this time last year. The inversion itself descended through the 847m level of this station, the change erratic and involving both rapid wind‐speed and temperature changes over very short periods.Our third paper is a preliminary review of the exceptional and record‐breaking rainfall in Cumbria in December by Stephen Burt, Mark McCarthy, Mike Kendon and Jamie Hannaford. ‘Cumbrian floods, 5/6 December 2015’ is on p. 36.On p. 40, we look at the effects on air quality of three large coal‐fired power stations in Yorkshire, as seen using satellite radiometry. In ‘Detection of the Yorkshire power stations from space: an air quality perspective’ Richard Pope and Miroslav Provod discuss the notable effects of these power stations, seen using 7‐year mean data, the level of pollution rivalling that of Manchester or London.Deciding where a high‐density network of automatic weather stations will give you the best information to plan for severe weather events is a complex matter. A great deal of information is now available for the environment, but it is necessary to bring these data together, as described in the method used in mountainous northern Turkey: ‘A GIS‐based siting technique for automatic weather stations in Trabzon, Turkey’ by Volkan Yildirim, Recep Nisanci, Ebru Husniye Colak and Okan Yildiz on p. 43.

A mid-Oligocene (Whitneyan) rhinocerotid from northeastern California

AbstractRhinoceroses were important in North American mammal faunas from the late middle Eocene to the Miocene, but the group’s poor sampling outside the High Plains and eastern Rocky Mountain regions during their early evolution significantly hinders understanding of their biogeography. This limited geographic sampling is particularly true of early–middle Oligocene time, with the vast majority of Whitneyan localities occurring in the White River Badlands of South Dakota. Thus, any rhinocerotid from outside the High Plains during this period is significant. We describe two new rhinocerotid specimens from the middle Oligocene Steamboat Formation of the northeastern Warner Mountains of California. Although the Steamboat Formation is well known for fossil plants, this is the first report of mammalian fossils from the area: an isolated lower molar recovered in 1974 but not previously described or illustrated, and a mandibular fragment recovered approximately 20 years later and bearing two molar teeth, most likely pertaining to the same taxon and horizon. The lack of distinctive morphological characters suggests both fossils be conservatively referred to Rhinocerotidae incertae sedis. Based on published tooth measurement data, Trigonias osborni represents the closest size match, but that species is currently only known from the Chadronian. Similarly, the Whitneyan taxon Diceratherium tridactylum is approximately the right size, but is currently only known from the High Plains and its presence in California would expand its geographic range substantially. Of greatest importance here is that sediments of the eastern Warner Mountains may represent a largely unexplored locale for early–middle Oligocene fossil vertebrates, and may yield important future finds.

Assessing Functional Role and Community Dynamics of Whitebark Pine at Alpine Treeline, Grand Teton National Park

Whitebark pine (Pinus albicaulis) is a keystone and foundation tree species in high elevation ecosystems of the Rocky Mountains. At alpine treelines along the eastern Rocky Mountain Front and in the Greater Yellowstone Ecosystem, whitebark pine often initiates tree islands through facilitation, thereby shaping vegetation pattern. This role will likely diminish if whitebark pine succumbs to white pine blister rust infection, climate change stress, and mountain pine beetle infestations. Here, we established baseline measurements of whitebark pine’s importance and blister infection rates at two alpine treelines in Grand Teton National Park. Our specific objectives were to: 1) examine the potential relationship between whitebark pine establishment and krummholz tree island formation at the upper alpine treeline ecotone in GTNP; 2) characterize blister rust infection rate and intensity at two treeline study areas and in whitebark pine growing both solitarily and within tree islands; and 3) characterize the biophysical environments a) where whitebark pine is/is not a majority tree island initiator, and b) with varying blister rust infection rates in treeline whitebark pine. In July 2015, we field-sampled treeline composition and blister rust infection in all krummholz whitebark pine in a total of 40 study plots. Preliminary results reveal: 1) that whitebark pine is a substantial component of treeline ecosystems, but is not a significant majority tree island initiator, and 2) blister rust infection levels for both study areas combined is 15.65%. Blister rust and mountain pine beetle interactions were not evident at the two study areas. This work provides important baseline measurements for understanding how community structure and composition may be altered given infestation by pathogens and pests in GTNP, especially in light of changing climate regimes.

MODIS Consistent Vegetation Parameter Specifications and Their Impacts on Regional Climate Simulations

Abstract A consistent set of Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation parameters, including leaf and stem area index (LAI and SAI, respectively), land-cover category (LCC), fractional vegetation cover (FVC), and albedo parameterization are developed, and their impacts on North American regional climate are evaluated based on 10-yr Climate–Weather and Research Forecasting Model (CWRF) simulations. As compared with the previous Advanced Very High Resolution Radiometer (AVHRR) set, MODIS LCC increases grassland and cropland fractions in the central Great Plains and Midwest, respectively. Evergreen needleleaf forest converts to mixed forest in the Southeast, and mixed forest converts to evergreen needleleaf in Canada. FVC decreases by 0.05–0.3 over the central Great Plains but increases by 0.1–0.35 over the northern Rocky Mountains, Canada, and the U.S. Southeast. MODIS LAI is less than AVHRR by 2–6, except in the central Great Plains, eastern Rocky Mountains, and central Mexico. LCC and FVC changes over the central Great Plains reduce CWRF warm biases by 0.71°C and wet biases by 0.36 mm day−1. Large LAI reductions cause latent and sensible heat fluxes to decrease by 0.78–5.81 and 0.91–6.54 W m−2, respectively. They also lessen cold biases over the Gulf States and Southeast and wet biases over the North American monsoon region and Canada during summer. In densely vegetated regions including eastern Canada, the Ohio Valley, and the mid-Atlantic region, spring and summer precipitation decreases and temperature increases result from LAI reductions that cause positive evapotranspiration–precipitation–soil moisture feedbacks. Conversely, precipitation and temperature decreases in sparely vegetated regions, such as the Great Plains, result from FVC reductions that cause negative albedo–evapotranspiration–precipitation–soil moisture feedbacks.

Redating the Mill Iron Site, Montana: A Reexamination of Goshen Complex Chronology

The Paleoindian Goshen complex occurs in the northern Plains and eastern Rocky Mountains. Since its identification, there has been much discussion about the chronological placement of the Goshen complex. This is especially true because diagnostic Goshen projectile points occur stratigraphically below Folsom artifacts at two sites, and early dates from the Mill Iron site, Montana, and the Hell Gap site, Wyoming, have suggested that this point type might be coeval with Clovis or the very earliest Folsom sites. This report presents new radiocarbon dates from the Mill Iron site, reviews Goshen chronology, and revises the age of the Goshen complex as 10,450 ± 15 to 10,175 ± 40 radiocarbon years B.P.

Increased Flight Altitudes among Migrating Golden Eagles Suggest Turbine Avoidance at a Rocky Mountain Wind Installation

Potential wind-energy development in the eastern Rocky Mountain foothills of British Columbia, Canada, raises concerns due to its overlap with a golden eagle (Aquila chrysaetos) migration corridor. The Dokie 1 Wind Energy Project is the first development in this area and stands as a model for other projects in the area because of regional consistency in topographic orientation and weather patterns. We visually tracked golden eagles over three fall migration seasons (2009–2011), one pre- and two post-construction, to document eagle flight behaviour in relation to a ridge-top wind energy development. We estimated three-dimensional positions of eagles in space as they migrated through our study site. Flight tracks were then incorporated into GIS to ascertain flight altitudes for eagles that flew over the ridge-top area (or turbine string). Individual flight paths were designated to a category of collision-risk based on flight altitude (e.g. flights within rotor-swept height; ≤150 m above ground) and wind speed (winds sufficient for the spinning of turbines; >6.8 km/h at ground level). Eagles were less likely to fly over the ridge-top area within rotor-swept height (risk zone) as wind speed increased, but were more likely to make such crosses under headwinds and tailwinds compared to western crosswinds. Most importantly, we observed a smaller proportion of flights within the risk zone at wind speeds sufficient for the spinning of turbines (higher-risk flights) during post-construction compared to pre-construction, suggesting that eagles showed detection and avoidance of turbines during migration.

Origin of glossic horizons in Cryalfs of the eastern Rocky Mountains, USA

Cryalfs are the predominant suborder along the eastern front of the Rocky Mountains from northern NM through MT and into Alberta. Approximately 50% of the Cryalfs in the western USA contain a glossic horizon, defined as a degraded argillic horizon containing properties of both an E and a Bt horizon. Using the NRCS database, we examined 257 Cryalf soil series, 79 of which contain a glossic horizon. The glossic horizon occurs at an average depth of 32cm and averages 24cm thick. The glossic horizon is most commonly an E/Bt with textures similar to the E above and Bt below. Waxy or glossy argillans are common, as well as clay-enriched nodules and seams. Laboratory data are available for only 10 Cryalf pedons containing a glossic horizon. Based on these data, the glossic horizon contains an average of 24% clay, 1.0 clay/CEC7, 0.6% organic C, a cation-exchange capacity of 19cmolc/kg soil, 85% base saturation, and a pH of 5.6. Several theories for the origin of the glossic horizon were considered from a weight-of-evidence approach. The glossic horizon in Cryalfs of the Rocky Mountains may be attributed to an input of eolian silt which creates a lithologic discontinuity and a mid-Holocene (5000yr BP to present) lowering of treeline containing the strongly podzolizing species Picea engelmannii and Abies lasiocarpa. Although glossic horizons are common in upper montane soils now containing lodgepole pine (Pinus contorta), they are uncommon in lower montane soils supporting lodgepole and ponderosa (Pinus ponderosa) pines.

Characterization of rhizosphere fungi from selenium hyperaccumulator and nonhyperaccumulator plants along the eastern Rocky Mountain Front Range

Selenium-hyperaccumulator plants can store over 1% (dry mass) Se in their tissues, despite the toxicity of this element at high concentrations across eukaryotes. These levels of Se can have widespread effects on the plant's ecological partners, including herbivores and pathogens. Still other partners seem to have coevolved Se tolerance. This is the first known study addressing the rhizosphere mycoflora of Se hyperaccumulators and aims to evaluate the rhizospheric fungal diversity and Se tolerance to further the knowledge of how these organisms interact with their host plants and survive in these extreme habitats. Rhizosphere fungi were isolated from Se-hyperaccumulator and nonaccumulator plant species collected from five sites in Colorado and Wyoming; four seleniferous sites and one nonseleniferous site. 259 isolates were identified to genus or species and evaluated for Se tolerance. Among the 24 represented genera, 11 comprised 86% of the isolates. The majority of isolates from the seleniferous sites were unaffected by 10 mg·L(-1) Se, irrespective of host plant (hyperaccumulator vs. nonaccumulator), while rhizosphere fungi from a control, nonseleniferous site were highly sensitive to Se at 10 mg·L(-1) and as a group were significantly less (α = 0.05) tolerant than the isolates from the seleniferous sites. Even though Se is a commonly used antifungal agent, these results suggest that rhizosphere fungi from seleniferous habitats have widespread Se tolerance, likely an adaptive advantage in their Se-rich habitat.

The magma and metal source of giant porphyry-type ore deposits, based on lead isotope microanalysis of individual fluid inclusions

The global supply of Mo and much of Cu and Au comes from porphyry-type ore deposits associated with hydrous magmas of broadly calc-alkaline composition, thought to be generated by contemporaneous subduction zone processes. Molybdenum is generally considered to be derived from the continental crust while Cu and Au are sourced in the mantle wedge above subducting slabs. Here we show that neither contemporaneous subduction nor derivation of Mo from crustal sources is required to explain the genesis of porphyry–Cu–Mo–Au deposits on Proterozoic lithosphere in the eastern Rocky Mountains. Uniform Pb isotope ratios measured by LA-MC-ICP-MS in individual fluid inclusions from distinct Cu–Au and later Mo ore-forming stages at Bingham Canyon, USA, demonstrate a common metal source. Uranogenic Pb isotope ratios are particularly non-radiogenic (17.494 < 206Pb/ 204Pb < 17.534; 15.553 < 207Pb/ 204Pb < 15.588) and plot to the left of the geochron and above the mantle Pb evolution line. In 207Pb/ 206Pb vs. 208Pb/ 206Pb space, the fluid Pb isotope data cluster at the non-radiogenic end of a mixing line described by > 80 feldspar data from igneous rocks intimately associated with magmatic-hydrothermal ore formation, which extends to modern depleted mantle or upper crust. Forward Monte Carlo simulations require three events for the U–Th–Pb isotope evolution of the fluid: (1) Late Archean formation of enriched crust is followed by (2) preferential extraction of Pb from this aged crust into a subduction fluid characterized by drastically reduced U/Pb that metasomatized lithospheric mantle at ∼ 1.8 Ga. This mantle reservoir then evolved to produce the retarded uranogenic Pb isotope signatures of the Bingham Canyon Cu–Mo–Au deposit in the Cenozoic (3). Similarly retarded uranogenic Pb isotope data characterize the giant porphyry–Mo and Climax-type Mo deposits of Henderson, Questa, Butte, and SE Arizona that occur in Proterozoic sutures of the central and eastern Rocky Mountains. We propose that Cenozoic melting of subcontinental lithospheric mantle metasomatized by subduction fluids during early Proterozoic amalgamation of terranes to the Wyoming Craton provides the metal endowment and subduction flavour to the giant magmatic-hydrothermal Cu–Mo–Au ore deposits in western North America, which together constitute the world's major molybdenum ore province.

Denning Chronology of Black Bears in Eastern Rocky Mountain National Park, Colorado

ABSTRACT. Understanding factors influencing the timing of den entrance and emergence of black bears (Ursus americanus) provides insight for bear management. We determined den entrance and emergence dates for bears in Rocky Mountain National Park (RMNP) and related these dates to vegetative productivity, weather, habitat, and demographic factors to assess the influence of these factors on denning chronology. Date of den entrance was most strongly influenced by age class, precipitation, and proportion of human-use areas in annual home ranges. Den entrance was typically later for adult bears during wetter years and when annual home ranges contained a greater proportion of human-use areas. Sex and presence of human-use areas were most strongly related to den emergence. Male bears typically emerged from dens before females, and bears emerged from dens earlier when human-use areas composed a greater proportion of annual home ranges. Collectively, our results suggest that denning behavior of black bears in RMNP ...

Population genetic data suggest a role for mosquito-mediated dispersal of West Nile virus across the western United States

After introduction, West Nile virus (WNV) spread rapidly across the western United States between the years 2001 and 2004. This westward movement is thought to have been mediated by random dispersive movements of resident birds. Little attention has been placed on the role of mosquito vectors in virus dispersal across North America. The mosquito vector largely responsible for WNV amplification and transmission of WNV in the western USA is Culex tarsalis. Here we present population genetic data that suggest a potential role for C. tarsalis in the dispersal of WNV across the western USA. Population genetic structure across the species range of C. tarsalis in the USA was characterized in 16 states using 12 microsatellite loci. structure and geneland analyses indicated the presence of three broad population clusters. Barriers to gene flow were resolved near the Sonoran desert in southern Arizona and between the eastern Rocky Mountains and High Plains plateau. Small genetic distances among populations within clusters indicated that gene flow was not obstructed over large portions of the West Coast and within the Great Plains region. Overall, gene flow in C. tarsalis appears to be extensive, potentially mediated by movement of mosquitoes among neighbouring populations and hindered in geographically limited parts of its range. The pattern of genetic clustering in C. tarsalis is congruent with the pattern of invasion of WNV across the western United States, raising the possibility that movement of this important vector may be involved in viral dispersal.

DOUGLAS-FIR GROWTH IN MOUNTAIN ECOSYSTEMS: WATER LIMITS TREE GROWTH FROM STAND TO REGION

The purpose of this work is to understand the nature of growth–climate relationships for Douglas-fir (Pseudotsuga menziesii) across the climatic dimensions of its niche. We used a combination of biophysically informed sampling (to identify sample sites) and dendroclimatology (to identify growth–climate relationships) along a climate gradient in northwestern United States mountain ecosystems from the western Olympic Peninsula, Washington to the eastern Rocky Mountain Front, Montana. We used a multi-scale sampling strategy that accounted for continentality, physiography, and topography as non-climatic factors that could influence climate and alter tree growth. We developed a network of 124 Douglas-fir tree-ring chronologies and explored growth–climate correlations across the sampled gradients. We considered two different spatial scales of monthly and seasonal climate variables as potential controlling factors on tree growth. Annual radial growth in 60–65% of the plots across the region is significantly correlated with precipitation, drought, or water balance during the late summer prior to growth and the early summer the year of growth. In a few plots, growth is positively correlated with cool-season temperature or negatively correlated with snowpack. Water availability is therefore more commonly limiting to Douglas-fir growth than energy limitations on growing season length. The first principal component derived from the chronologies is significantly correlated with independent drought reconstructions. The sensitivity of Douglas-fir to summer water balance deficit (potential evapotranspiration minus actual evapotranspiration) indicates that increases in April to September temperature without increases in summer precipitation or soil moisture reserves are likely to cause decreases in growth over much of the sampled area, especially east of the Cascade crest. In contrast, Douglas-fir may exhibit growth increases at some higher elevation sites where seasonal photosynthesis is currently limited by growing-season length or low growing-season temperature. Life-history processes such as establishment, growth, and mortality are precursors to changes in biogeography, and measurements of climate effects on those processes can provide early indications of climate-change effects on ecosystems.

Climatic and hydrologic variability during the past millennium in the eastern Rocky Mountains and northern Great Plains of western Canada

Modelling of tree-ring δ 13C and δ 18O data from the Columbia Icefield area in the eastern Rocky Mountains of western Canada provides fuller understanding of climatic and hydrologic variability over the past 1000 yr in this region, based on reconstruction of changes in growth season atmospheric relative humidity ( RH grs), winter temperature ( T win) and the precipitation δ 18O– T win relation. The Little Ice Age (~ AD 1530s–1890s) is marked by low RH grs and T win and a δ 18O– T win relation offset from that of the present, reflecting enhanced meridional circulation and persistent influence of Arctic air masses. Independent proxy hydrologic evidence suggests that snowmelt sustained relatively abundant streamflow at this time in rivers draining the eastern Rockies. In contrast, the early millennium was marked by higher RH grs and T win and a δ 18O– T win relation like that of the 20th century, consistent with pervasive influence of Pacific air masses because of strong zonal circulation. Especially mild conditions prevailed during the “Medieval Climate Anomaly” ~ AD 1100–1250, corresponding with evidence for reduced discharge in rivers draining the eastern Rockies and extensive hydrological drought in neighbouring western USA.

Assessing exotic plant species invasions and associated soil characteristics: A case study in eastern Rocky Mountain National Park, Colorado, USA, using the pixel nested plot design

Rocky Mountain National Park (RMNP), Colorado, USA, contains a diversity of plant species. However, many exotic plant species have become established, potentially impacting the structure and function of native plant communities. Our goal was to quantify patterns of exotic plant species in relation to native plant species, soil characteristics, and other abiotic factors that may indicate or predict their establishment and success. Our research approach for field data collection was based on a field plot design called the pixel nested plot. The pixel nested plot provides a link to multi-phase and multi-scale spatial modeling-mapping techniques that can be used to estimate total species richness and patterns of plant diversity at finer landscape scales. Within the eastern region of RMNP, in an area of approximately 35,000 ha, we established a total of 60 pixel nested plots in 9 vegetation types. We used canonical correspondence analysis (CCA) and multiple linear regressions to quantify relationships between soil characteristics and native and exotic plant species richness and cover. We also used linear correlation, spatial autocorrelation and cross correlation statistics to test for the spatial patterns of variables of interest. CCA showed that exotic species were significantly ( P < 0.05) associated with photosynthetically active radiation ( r = 0.55), soil nitrogen ( r = 0.58) and bare ground ( r = −0.66). Pearson's correlation statistic showed significant linear relationships between exotic species, organic carbon, soil nitrogen, and bare ground. While spatial autocorrelations indicated that our 60 pixel nested plots were spatially independent, the cross correlation statistics indicated that exotic plant species were spatially associated with bare ground, in general, exotic plant species were most abundant in areas of high native species richness. This indicates that resource managers should focus on the protection of relatively rare native rich sites with little canopy cover, and fertile soils. Using the pixel nested plot approach for data collection can facilitate the ecological monitoring of these vulnerable areas at the landscape scale in a time- and cost-effective manner.

40Ar/39Ar thermochronology constraints on the timing of Proterozoic basement exhumation and fault ancestry, southern Sangre de Cristo Range, New Mexico

Proterozoic ancestry is increasingly being proposed for both Ancestral Rocky Mountain (Pennsylvanian-Permian) and Laramide-age (Late Cretaceous–early Tertiary) faults in the southwestern United States. We test this hypothesis by using 40 Ar/ 39 Ar thermochronology on Proterozoic basement rocks in the southern Sangre de Cristo Range, New Mexico. Hornblende and mica yield ages consistent with basement rocks cooling below ∼500 °C after ca. 1.4 Ga regional metamorphism, followed by protracted basement residence at temperatures between 300 and 400 °C until the Neoproterozoic. K-feldspar age spectra are dominated by Neoproterozoic apparent ages and constrain basement exhumation from mid-crustal depths (∼10 km) to within a few kilometers of the surface during the Neoproterozoic. Samples were also collected across the north-striking, steeply west-dipping Montezuma fault, which bounds the eastern Rocky Mountain range front and has known Ancestral Rocky Mountain and Laramide-age movement. Contrasting 40 Ar/ 39 Ar K-feldspar–derived thermal histories from opposing sides of the fault require two episodes of Neoproterozoic fault movement. Overall, rocks to the west record multiple diffusion domain (MDD) thermal histories, which indicate that cooling was caused by 5–7 km of basement exhumation between 1000 and 800 Ma, whereas rocks to the east were exhumed later, between 750 and 600 Ma. Assuming that the present-day fault geometry was established in the Proterozoic, west-side-up throw late in the Grenville orogeny (ca. 1000 Ma) accommodated east-west shortening. West-side-down extensional movement at ca. 750 Ma is inferred to be associated with the incipient rifting of the supercontinent Rodinia.

On the farm front: the Women's Land Army in World War II

Rosie the Riveter has become an icon for working women's contributions to World War II, but more than three million women also labored on America's agricultural front. The Women's Land Army - consisting largely of urban homemakers, office and industrial workers, and students - put women to work caring for livestock; laboring in dairies and canneries; and planting, cultivating, and harvesting crops. Accounting for the majority of wartime farm labor, these remarkable women helped to ensure both Freedom from Want at home and victory abroad. In 1943 the government formed the Women's Land Army as part of the Emergency Farm Labor Program, placing its workers in areas where American farmers urgently needed assistance. Many farmers in even the most desperate areas, however, initially opposed women working their land. Rural administrators in the Midwest and the South yielded to necessity and employed several hundred thousand women as farm laborers by the end of the war, but those in the Great Plains and eastern Rocky Mountains remained hesitant, suffering serious agricultural and financial losses as a consequence. Placing agricultural work in the larger context of twentieth-century women's labor history, Carpenter shows how the WLA changed the national view of farming. By accepting all available women as agricultural workers, farmers abandoned traditional labor and stereotypical social practices. When the WLA officially disbanded in 1945, many members remained in their agricultural jobs rather than return to a full-time home life or their prewar employment. Shedding new light on women who responded to the call of their country, On the Farm Front for the first time illuminates the Women's Land Army's unique contribution to prosperity and victory, and to changing women's role in American society.