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At least 289 records · Page 16Linked to original sources
USGS2008

Species traits influence the genetic consequences of river fragmentation on two co-occurring redhorse (Moxostoma) species

We used microsatellite DNA markers to test whether fragmentation of the Trent River (Ontario, Canada) has reduced genetic diversity and increased genetic differentiation among populations of river redhorse (Moxostoma carinatum) and shorthead redhorse (Moxostoma macrolepidotum). Allelic richness of both species was significantly greater along the free-flowing Muskegon River (Michigan, USA) than along the fragmented Trent River. Contrary to expectations, there was no evidence of a fragment length effect on genetic diversity, recent population bottlenecks, or increased relatedness among individuals in fragmented populations. High levels of linkage disequilibrium indicate extinction-recolonization population dynamics along the Trent River. For both species, pairwise FST tests identified weak but statistically significant population differentiation. In the Trent River, differentiation was significantly greater for river redhorse than for shorthead redhorse and, for both species, greater than in the Muskegon River. Moderate fragmentation effects likely reflect the permeability of the dam-lock system to redhorse movement. Differences between species indicate that as a result of smaller effective population sizes, habitat specialists and species at the periphery of their geographic range are more sensitive to river fragmentation. ?? 2008 NRC.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2009

Summary of West Virginia Water-Resource Data through September 2008

The West Virginia Water Science Center of the U.S. Geological Survey, in cooperation with State and Federal agencies, obtains a large amount of data pertaining to the water resources of West Virginia each water year. A water year is the 12-month period beginning October 1 and ending September 30. These data, accumulated during many years, constitute a valuable database for developing an improved understanding of the water resources of the State. These data are maintained in the National Water Information System (NWIS) and are available through its World-Wide Web interface, NWISWeb, at http://waterdata.usgs.gov/wv/nwis. Data can be retrieved in a variety of common formats, and a tutorial is available at http://nwis.waterdata.usgs.gov/tutorial. Location information for all continuous-record gaging stations operated in West Virginia through September 2008 is provided in this report, as well as statistical summaries of the available daily records. This report can serve as an index to the daily records data available on the World-Wide Web. Hydrologic data for nearly all of the gaging stations identified in this report are also available in the annual publication series titled Water-Resources Data - West Virginia. This series of annual reports for West Virginia began with the 1961 water year with a report that contained only data relating to quantities of surface water. For the 1964 water year, a similar report was introduced that contained only data relating to water quality. Beginning with the 1975 water year, the report format was changed to include data on quantities of surface water, quality of surface water and groundwater, and groundwater levels. Prior to the introduction of the Water-Resources Data - West Virginia series and for several water years concurrent with it, water-resources data for West Virginia were published in U.S. Geological Survey Water-Supply Papers. Data on stream discharge and stage and on lake or reservoir contents and stage through September 1960 were published annually under the title Surface-Water Supply of the United States, Parts 6A and 6B. For the 1961 through 1970 water years, the data were published in two 5-year reports. Data on chemical quality, temperature, and suspended sediment for the 1941 through 1970 water years were published annually under the title Quality of Surface Water of the United States, and water levels for the 1935 through 1974 water years were published under the title Ground-Water Levels in the United States. Many of the above mentioned Water-Supply Papers are available at the USGS Publications Warehouse (http://pubs.er.usgs.gov), and most of the others may be found in the collections of large libraries or may be purchased from the U.S. Geological Survey, Books and Open-File Reports, Federal Center, Box 25425, Denver, Colorado 80225. Annual reports on hydrologic data are published by the Geological Survey for all states, and each has an identification number consisting of the two-letter state abbreviation, the last two digits of the water year, and the volume number. For example, the 2005 water year report for West Virginia is identified as U.S. Geological Survey Water-Data Report WV-05-01. Water-Data Reports for West Virginia for 2001-2005 are available online at http://pubs.usgs.gov/wdr/#WV. Water-Data Reports for water years prior to 2006 are for sale in paper copy or microfiche by the National Technical Information Service, U.S. Department of Commerce, Springfield, Virginia 22161. Since the 2006 water year, the report is published online only and is available at http://wdr.water.usgs.gov/. When substantial errors in published records are discovered, the records are revised. Such revisions are routine and are made to records regardless of the age of the original records. Revisions have been made for many stations for which data are published in this report. The USGS National Water Information System always contains the most recent data revisions. For critical a

Open-File Report↗
USGS1986

Southern hemisphere origin of the Cretaceous Laytonville Limestone of California

New paleomagnetic, paleontologic, and stratigraphic data from outcrops of the Laytonville Limestone (101 to 88 million years old) support a Southern Hemisphere orgin. A paleomagnetic megaconglomerate test is statistically significant and suggests magnetization at 14?? ?? 5?? south, predating Late Cretaceous to Eocene (70 to 50 million years ago) accretion. Rapid Kula plate movement or the existence and demise of a now vanished oceanic plate (or both) are required to accommodate the greater than 50?? of poleward displacement implied by the paleomagnetic data. This rapid motion brings into question the validity of a "speed limit" for absolute plate velocity based on present-day plate motions.

Science↗
USGS2008

Significance of model credibility in estimating climate projection distributions for regional hydroclimatological risk assessments

Ensembles of historical climate simulations and climate projections from the World Climate Research Programme's (WCRP's) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset were investigated to determine how model credibility affects apparent relative scenario likelihoods in regional risk assessments. Methods were developed and applied in a Northern California case study. An ensemble of 59 twentieth century climate simulations from 17 WCRP CMIP3 models was analyzed to evaluate relative model credibility associated with a 75-member projection ensemble from the same 17 models. Credibility was assessed based on how models realistically reproduced selected statistics of historical climate relevant to California climatology. Metrics of this credibility were used to derive relative model weights leading to weight-threshold culling of models contributing to the projection ensemble. Density functions were then estimated for two projected quantities (temperature and precipitation), with and without considering credibility-based ensemble reductions. An analysis for Northern California showed that, while some models seem more capable at recreating limited aspects twentieth century climate, the overall tendency is for comparable model performance when several credibility measures are combined. Use of these metrics to decide which models to include in density function development led to local adjustments to function shapes, but led to limited affect on breadth and central tendency, which were found to be more influenced by 'completeness' of the original ensemble in terms of models and emissions pathways. ?? 2007 Springer Science+Business Media B.V.

Climatic Change↗
USGS2016

A global review of freshwater crayfish temperature tolerance, preference, and optimal growth

Conservation efforts, environmental planning, and management must account for ongoing ecosystem alteration due to a changing climate, introduced species, and shifting land use. This type of management can be facilitated by an understanding of the thermal ecology of aquatic organisms. However, information on thermal ecology for entire taxonomic groups is rarely compiled or summarized, and reviews of the science can facilitate its advancement. Crayfish are one of the most globally threatened taxa, and ongoing declines and extirpation could have serious consequences on aquatic ecosystem function due to their significant biomass and ecosystem roles. Our goal was to review the literature on thermal ecology for freshwater crayfish worldwide, with emphasis on studies that estimated temperature tolerance, temperature preference, or optimal growth. We also explored relationships between temperature metrics and species distributions. We located 56 studies containing information for at least one of those three metrics, which covered approximately 6 % of extant crayfish species worldwide. Information on one or more metrics existed for all 3 genera of Astacidae, 4 of the 12 genera of Cambaridae, and 3 of the 15 genera of Parastacidae. Investigations employed numerous methodological approaches for estimating these parameters, which restricts comparisons among and within species. The only statistically significant relationship we observed between a temperature metric and species range was a negative linear relationship between absolute latitude and optimal growth temperature. We recommend expansion of studies examining the thermal ecology of freshwater crayfish and identify and discuss methodological approaches that can improve standardization and comparability among studies.

Reviews in Fish Biology and Fisheries↗
USGS2022

Estimating catch curve mortality based on relative return rates of coded wire tagged lake trout in US waters of Lake Huron

We estimated total mortality using catch curves based on relative return rates (RRs) of coded wire tagged lake trout ( Salvelinus namaycush ) in US waters of Lake Huron. RR was calculated as age-specific CPUE per million of fish stocked. Annual mortality for the late 1990s through early 2000s was estimated as 38% from the 1991–1995 year classes, with an effective age range of 5–10 years, and then was estimated as 24% for the post-2000 period from the 1996–2009 year classes. The two estimates from simple catch curve regressions based on average RR at age values were the same as from a mixed model with individual RR values from all stocking events. These two estimates were also comparable to the findings from statistical catch-at-age assessments with fundamentally different assumptions. Our approach is not constrained by the assumption that the expected recruitment is a constant over time and thus has the advantage to use multiple observations on each age from multiple cohorts. Our approach has broad applicability to aquatic ecosystems in which multiple mark-and-release events of fish stocking have been implemented.

Michigan↗
USGS2020

Good practices for species distribution modeling of deep-sea corals and sponges for resource management: Data collection, analysis, validation, and communication

Resource managers in the United States and worldwide are tasked with identifying and mitigating trade-offs between human activities in the deep sea (e.g., fishing, energy development, and mining) and their impacts on habitat-forming invertebrates, including deep-sea corals and sponges (DSCS). Related management decisions require information about where DSCS occur and in what densities. Species distribution modeling (SDM) provides a cost-effective means of identifying potential DSCS habitat over large areas to inform these management decisions and data collection. Here we describe good practices for DSCS SDM, especially in the context of data collection and management applications. Managers typically need information regarding DSCS encounter probabilities, densities, and sizes, defined at sub-regional to basin-wide scales and validated using subsequent, targeted data collections. To realistically achieve these goals, we suggest analysts: 1) integrate available data sources in SDMs including fine-scale visual sampling and broad-scale resource surveys (e.g., fisheries trawl surveys); and 2) include environmental predictor variables representing multiple spatial scales, model residual spatial autocorrelation, and quantify prediction uncertainty. When possible, models fitted to presence-absence and density data are preferred over models fitted only to presence data, which are difficult to validate and can confound estimated probability of occurrence or density with sampling effort. Ensembles of models can provide robust predictions, while multi-species models leverage information across taxa and facilitate community inference. To facilitate the use of models by managers, predictions should be expressed in units that are widely understood and validated at an appropriate spatial scale using a sampling design that provides strong statistical inference. We present three case studies for the Pacific Ocean that illustrate good practices with respect to data collection, modeling, and validation; these case studies demonstrate it is possible to implement our good practices in real-world settings.

Frontiers in Marine Science↗
USGS2023

Temporal, environmental, and demographic correlates of Ichthyophonus sp. infections in mature Pacific herring populations

Causes of population collapse and failed recovery often remain enigmatic in marine forage fish like Pacific herring ( Clupea pallasii ) that experience dramatic population oscillations. Diseases such as ichthyophoniasis are hypothesized to contribute to these declines, but lack of long-term datasets frequently prevents inference. Analysis of pathogen surveillance and population assessment datasets spanning 2007–2019 indicate that the age-based prevalence estimate of Ichthyophonus infection was, on average, 54% greater among a collapsed population of Pacific herring (Prince William Sound, Alaska, USA) as compared to a nearby population (Sitka Sound, Alaska, USA) that is relatively robust. During the study years, the age-based infection prevalence ranged from 14 to 44% in Prince William Sound and 5 to 33% in Sitka Sound. At both sites, the age-based infection prevalence declined over time, with an average decrease of 7% per year. Statistical analyses indicated that infection prevalence between the two populations was reduced by regional factors affecting both sites, and that these factors were independent of herring density. Infection prevalence in both populations was positively correlated with herring age and negatively correlated with the Pacific Decadal Oscillation. This study demonstrates how synthesis of environmental, stock assessment, and disease assessment data can be leveraged to elucidate epidemiological trends in diseases of wild fish.

ICES Journal of Marine Science↗
USGS2024

Individual-based ecological particle tracking model (ECO-PTM) for simulating juvenile chinook salmon migration and survival through the Sacramento – San Joaquin Delta

Recovery of endangered salmon species in the Central Valley of California amidst prolonged drought and climate change necessitates innovative water management actions that balance species recovery and California's water demands. We describe an individual-based ecological particle tracking model (ECO-PTM) that can be used to assess the efficacy of proposed actions. Based on a random walk theory, the model tracks individual particles’ travel time, routing and survival in a flow field simulated by the Delta Simulation Model 2 hydrodynamic module (DSM2 HYDRO). The random walk particles are parameterized to have fish-like swimming behaviors, including upstream/downstream swimming, probabilistic holding behaviors, and stochastic swimming velocities. Particle routing at key junctions is based on well-established statistical models, and route-specific survival is calculated using the XT mean free-path length model. Behavioral parameters were estimated by fitting several competing models to a multiyear dataset of travel times from acoustic tagged juvenile salmon. The model’s baseline simulations under historical flow conditions from 1991 to 2016 successfully replicated essential relationships between salmon outmigration survival and hydrodynamic conditions, consistent with previous studies and the STARS (Survival Travel Time and Routing Simulation) statistical simulation model. Simulation results for management scenarios revealed multifaceted influences on fish survival, including Delta flow, flow at key junctions, route alterations, seasons, and water year characteristics. Importantly, these results highlight ECO-PTM’s potential to predict fish survival outcomes of proposed actions, serving as a foundation for informed future research, decision-making, and effective management strategies to enhance the survival prospects of out-migrating salmonids within the Sacramento-San Joaquin Delta ecosystem.

California↗
USGS2000

Water quality modeling in the systems impact assessment model for the Klamath River basin - Keno, Oregon to Seiad Valley, California

This report describes the water quality model developed for the Klamath River System Impact Assessment Model (SIAM). The Klamath River SIAM is a decision support system developed by the authors and other US Geological Survey (USGS), Midcontinent Ecological Science Center staff to study the effects of basin-wide water management decisions on anadromous fish in the Klamath River. The Army Corps of Engineersa?? HEC5Q water quality modeling software was used to simulate water temperature, dissolved oxygen and conductivity in 100 miles of the Klamath River Basin in Oregon and California. The water quality model simulated three reservoirs and the mainstem Klamath River influenced by the Shasta and Scott River tributaries. Model development, calibration and two validation exercises are described as well as the integration of the water quality model into the SIAM decision support system software. Within SIAM, data are exchanged between the water quantity model (MODSIM), the water quality model (HEC5Q), the salmon population model (SALMOD) and methods for evaluating ecosystem health. The overall predictive ability of the water quality model is described in the context of calibration and validation error statistics. Applications of SIAM and the water quality model are described.

California, Oregon↗
USGS2026

Evaluating the effects of a multi-modal deterrent on upstream passage by invasive carp and native species

Invasive carp, including Silver Carp ( Hypophthalmichthys molitrix ) and Grass Carp ( Ctenopharyngodon idella ), are increasing their range within the Mississippi River Basin, threatening native fishes and ecosystem function. We conducted a 3-year field test of a multi-modal deterrent that uses sound, bubbles, and light to test its ability to impede upstream passage by invasive carp. The test was performed at a lock and dam on the Cumberland River, Kentucky, USA, using acoustic telemetry to track the movements of Silver Carp, Grass Carp, and several native fish species. When the deterrent was operating, the estimated probability of upstream lock passage was 53% lower (95% CI: 41%–63%) for Silver Carp but 74% higher (95% CI: 3%–190%) for Grass Carp compared to times when the deterrent was not operating. Paddlefish ( Polyodon spathula ) passage was reduced by 43% (95% CI: 71% reduction to 9% increase), although this was not statistically significant. We detected no significant effects on Freshwater Drum ( Aplodinotus grunniens ) or Smallmouth Buffalo ( Ictiobus bubalus ). However, sample sizes were small for these native species, limiting our ability to identify effects. Water temperature, tailwater elevation, and vessel lockages affected passage rates, although this varied among species.

Kentucky↗
USGS2026

Guidelines for producing integrated 210Pb and 14C age-models

Accurate reconstructions of past environmental changes are crucial in paleoecological research and require reliable chronologies of sedimentary archives. Establishing robust age-models and obtaining the most appropriate proxies for analysis is a complex scientific endeavor, requiring extensive resources and collaboration among specialists, including radiochronologists. Radiometric dating methods, such as 210 Pb and radiocarbon ( 14 C), are frequently employed to establish chronologies in aquatic sedimentary deposits and peat bogs. In this study, we review key aspects of sampling, analysis, and the principles underlying 210 Pb and 14 C age-models, focusing on methods for developing robust joint chronologies for paleoenvironmental research. Drawing largely from the authors' experiences and group discussions during and after a scientific workshop in 2022, we discuss important considerations for site selection, sampling strategies, and radiometric dating to construct integrated 210 Pb and 14 C age-models. Using expert consensus, this group – called Paleostats – aims to provide a set of best practices for other geochronologists with this methods paper. Among our conclusions, we emphasize the importance of accounting for site-specific factors such as prior information on sedimentation rates to establish appropriate sampling and analytical strategies. The use of appropriate coring devices can minimize disturbance to sediments and ensure the core surface remains intact and preserved until sectioning. Where excess 210 Pb is expected, sectioning at intervals of ≤1 cm provides an adequate sampling resolution for 210 Pb dating. Exceptions are possible, allowing for ~2–3 cm sections in areas with confirmed high sedimentation rates (e.g., > 1 cm yr −1 ). Recovering deeper core sections for 14 C dating with sufficient overlap allows for accounting errors in depth estimates made in the field. Special attention is advised during time intervals where validation proxies, such as the human-made radionuclides 137 Cs or post-bomb 14 C, are expected, and to determine the depth of secular equilibrium between 210 Pb and 226 Ra. Radiocarbon analyses are commonly performed by accelerator mass spectrometry, and age models are constructed mainly using Bayesian statistics with Markov Chain Monte Carlo techniques (e.g., Bacon ). A Bayesian approach ( Plum ) is now available for producing 210 Pb age-models, which infers the 210 Pb ex flux, eliminates the need for selecting an equilibrium depth, and allows dating cores with incomplete 210 Pb ex inventory. Plum offers improved chronologies by integrating raw 210 Pb and 14 C data, and these age-models can be enriched with other dating methodologies, such as identifying tephras and other well-recorded historical events. Harmonized reporting would contribute to making radiometric age-models reproducible, which would benefit from an international effort. Using 210 Pb and 14 C to produce integrated age-models may yield better insights into the interplay between natural and recent anthropogenic forcings on ecosystems. This can enhance our understanding of environmental processes and their impacts on climate change, ultimately supporting science-based assessments and decisions.

Earth-Science Reviews↗
USGS2020

Well predictive performance of play-wide and Subarea Random Forest models for Bakken productivity

In recent years, geologists and petroleum engineers have struggled to clearly identify the mechanisms that drive productivity in horizontal, hydraulically-fractured oil wells producing from the middle member of the Bakken formation. This paper fills a gap in the literature by showing how this play’s heterogeneity affects factors that drive well productivity. It is important because understanding the relative strength of productivity drivers and how predictors vary spatially facilitates best-practices for well site selection and well completion design. The paper describes an application of the Random Forest (RF) machine learning technique to identify these mechanisms and to evaluate their importance across 9 subareas of the North Dakota portion of the Bakken play. The study examined productivity of 7311 wells initiating production from 2010 through 2017. Well productivity varied considerably across the 9 subareas within the play, so it was not surprising that the dominant predictors, the initial 180-day water cut and the 30-day initial gas production, vary spatially to mirror local conditions that strongly affect well productivity. The relative importance of well completion predictor variables, that is, the numbers of fractures stages per well, volume of injected proppant per stage, volume of injected fluids per stage, and lateral length, varied considerably across the subareas. Statistical permutation tests are presented that generally confirm the importance rankings. Subarea Random Forest models explained from 50 percent to 82 percent of the variation in productivity test samples while the play-wide model explained 73 percent of the test sample well productivity. Weakness in the predictive ability of the Random Forest models are traced to the limited variability in the training data. Implications of the empirical findings regarding the Bakken play for operators and for research and government institutions are discussed in the concluding section.

Montana, North Dakota, South Dakota↗
USGS2026

Patterns and drivers of cliff erosion in Big Sur, California, USA using repeat photogrammetry, 2017–2023

Seacliff erosion in steep terrain poses major risks to transportation and critical infrastructure. In Big Sur, California, USA, seacliff erosion threatens the sustainability of the central coast stretch of California State Route 1, a transportation corridor that is critical to the region's economy. Published cliff retreat rates for the region range from 1 to 40 cm yr −1 , highlighting that high-resolution, process-based studies could enhance understanding of the causes of spatial and temporal variability. We quantified cliff erosion and investigated its drivers along ∼13 km of the Big Sur coastline at week–month timescales during the late fall to early spring wet seasons between January 2017 and June 2023 by analyzing 3D point clouds developed from aerial imagery using four-dimensional structure-from-motion (4D SfM) photogrammetry techniques. We calculated cliff face retreat rates of 2.23 ± 3.06 cm yr −1 (mean ±1 σ ), an order of magnitude lower than long-term estimated rates for the region (which included large deep-seated landslides), but in line with short-term rates reported across California. Change detection imagery comparison, cliff profiles through time, and statistical analysis reveal a cyclical cliff evolution process in which erosion by wave action at the cliff base destabilizes the cliff and primes it for subsequent failure during precipitation events. Although more erosion by volume could be attributed to precipitation-induced increases in soil moisture (784 m 3 km −1 yr −1 ) compared with erosion attributed to wave power (282 m 3 km −1 yr −1 ), our observations underscore the coupled nature of these processes in driving cliff evolution, consistent with established theory and observations.

California↗
USGS2019

Drift and beaching patterns of sea otter carcasses and car tire dummies

Enumerating and examining marine animal carcasses is important for quantifying mortality rates and determining causes of mortality. Drifter experiments are one tool for estimating at‐sea mortality and determining factors affecting carcass drift, but they require validation to confirm drifters accurately replicate the drift characteristics of the species of interest. The goal of this study was to determine whether dummies constructed from car tires were appropriate substitutes for sea otter ( Enhydra lutris ) carcasses. We released 33 sets of targets (carcasses and dummies) in a one‐to‐one ratio on 15 randomly chosen dates between January 1995 and December 1996. They were telemetrically tracked until they beached or were no longer detected. Beaching rates were similar between carcasses (69.7%) and dummies (66.7%). Our results indicated that there was no statistical difference in the drifting pattern, as measured by distance traveled and location, between carcasses and dummies, and that cumulative wind speed, days since release, and release month were predictors of drift patterns. We concluded that dummies constructed from car tires do imitate sea otter carcasses and could be used to estimate at‐sea mortality of sea otters, or, if released during or after an oil spill, could be used to direct search efforts for carcasses.

California↗
USGS2006

Predicting water-surface fluctuation of continental lakes: A RS and GIS based approach in Central Mexico

Changes in the water-surface area occupied by the Cuitzeo Lake, Mexico, during the 1974-2001 period are analysed in this study. The research is based on remote sensing and geographic information techniques, as well as statistical analysis. High-resolution satellite image data were used to analyse the 1974-2000 period, and very low-resolution satellite image data were used for the 1997-2001 period. The long-term analysis (1974-2000) indicated that there were temporal changes in the surface area of the Cuitzeo Lake and that these changes were related to precipitation and temperatures that occurred in the previous year. Short-term monitoring (1997-2001) showed that the Cuitzeo Lake surface is lowering. Field observations demonstrated also that yearly desiccation is recurrent, particularly, in the western section of the lake. Results suggested that this behaviour was probably due to a drought period in the basin that began in the mid 1990s. Regression models constructed from long-term data showed that fluctuations of lake level can be estimated by monthly mean precipitation and temperatures of the previous year. ?? Springer Science + Business Media, Inc. 2006.

Water Resources Management↗
USGS2003

Using multiple logistic regression and GIS technology to predict landslide hazard in northeast Kansas, USA

Landslides in the hilly terrain along the Kansas and Missouri rivers in northeastern Kansas have caused millions of dollars in property damage during the last decade. To address this problem, a statistical method called multiple logistic regression has been used to create a landslide-hazard map for Atchison, Kansas, and surrounding areas. Data included digitized geology, slopes, and landslides, manipulated using ArcView GIS. Logistic regression relates predictor variables to the occurrence or nonoccurrence of landslides within geographic cells and uses the relationship to produce a map showing the probability of future landslides, given local slopes and geologic units. Results indicated that slope is the most important variable for estimating landslide hazard in the study area. Geologic units consisting mostly of shale, siltstone, and sandstone were most susceptible to landslides. Soil type and aspect ratio were considered but excluded from the final analysis because these variables did not significantly add to the predictive power of the logistic regression. Soil types were highly correlated with the geologic units, and no significant relationships existed between landslides and slope aspect. ?? 2003 Elsevier Science B.V. All rights reserved.

Engineering Geology↗
USGS2017

Distributional changes and range predictions of downy brome (Bromus tectorum) in Rocky Mountain National Park

Downy brome (Bromus tectorum L.), an invasive winter annual grass, may be increasing in extent and abundance at high elevations in the western United States. This would pose a great threat to high-elevation plant communities and resources. However, data to track this species in high-elevation environments are limited. To address changes in the distribution and abundance of downy brome and the factors most associated with its occurrence, we used field sampling and statistical methods, and niche modeling. In 2007, we resampled plots from two vegetation surveys in Rocky Mountain National Park for presence and cover of downy brome. One survey was established in 1993 and had been resampled in 1999. The other survey was established in 1996 and had not been resampled until our study. Although not all comparisons between years demonstrated significant changes in downy brome abundance, its mean cover increased nearly fivefold from 1993 (0.7%) to 2007 (3.6%) in one of the two vegetation surveys (P = 0.06). Although the average cover of downy brome within the second survey appeared to be increasing from 1996 to 2007, this slight change from 0.5% to 1.2% was not statistically significant (P = 0.24). Downy brome was present in 50% more plots in 1999 than in 1993 (P = 0.02) in the first survey. In the second survey, downy brome was present in 30% more plots in 2007 than in 1996 (P = 0.08). Maxent, a species-environmental matching model, was generally able to predict occurrences of downy brome, as new locations were in the ranges predicted by earlier generated models. The model found that distance to roads, elevation, and vegetation community influenced the predictions most. The strong response of downy brome to interannual environmental variability makes detecting change challenging, especially with small sample sizes. However, our results suggest that the area in which downy brome occurs is likely increasing in Rocky Mountain National Park through increased frequency and cover. Field surveys along with predictive modeling will be vital in directing efforts to manage this highly invasive species. ?? Weed Science Society of America 2011.

Invasive Plant Science and Management↗