Northwestern Colorado Research Articles

A new Late Cretaceous metatherian from the Williams Fork Formation, Colorado.

Heleocola piceanus, a new, relatively large metatherian from Upper Cretaceous ('Edmontonian') strata of the Williams Fork Formation in northwestern Colorado is described, based on a recently discovered jaw fragment (MWC 9744), in addition to three isolated teeth initially referred by other studies to Aquiladelphis incus and Glasbius piceanus. Although sharing several morphologic characters with the Lancian genus Glasbius, H. piceanus lower molars are considerably larger than those of Glasbius and differ from the latter in lacking a buccal cingulid, possessing carnassiform notches on the cristid obliqua and entocristid, and bearing an entoconulid on m3. To examine the relationship of Heleocola piceanus to other metatherians, H. piceanus was scored into a previously existing taxon-character matrix. Our phylogenetic analysis recovers H. piceanus as the sister taxon to Glasbius, which is consistent with our morphologic comparisons. H. piceanus represents the oldest member of the Glasbiidae. A regression equation for predicting body mass of dentally conservative metatherians that utilizes the length of m1 estimates the mass of H. piceanus at 855-1170 g, which is comparable in mass to today's muskrat (Ondatra zibethicus) and large relative to other Late Cretaceous pediomyoids. Based upon its molar morphology, specifically the low inflated cusps, low height differential between the trigonid and talonid, and near-bunodont morphology, H. piceanus is interpreted as an omnivore with a plant-dominated diet.

Concurrence of Late Triassic lithostratigraphic, radioisotopic, and biostratigraphic data support a Carnian age for the Popo Agie Formation (Chugwater Group), Wyoming, USA

The Upper Triassic Popo Agie Formation of the Chugwater Group of Wyoming, northeastern Utah, and northwestern Colorado has been an enigmatic unit since its definition and is commonly excluded from large-scale studies of continental Upper Triassic strata in the western USA. Lithostratigraphic correlations of Popo Agie Formation outcrops are documented from west-central Wyoming through northeastern Utah and northwestern Colorado, which demonstrates the presence of the Popo Agie Formation throughout this region. Unique detrital zircon age distributions have led previous workers to hypothesize a paleodrainage connecting basal units of the Dockum in west Texas and eastern New Mexico, USA, with the Gartra Grit, a basal unit of the Popo Agie in northeastern Utah. Biostratigraphically informative taxa such as parasuchid phytosaurs in the absence of leptosuchmorph phytosaurs support an assignment of the Gartra Grit and Popo Agie Formation to the Otischalkian estimated holochronozone. We present the first detrital zircon age distributions for the Popo Agie Formation. Multidimensional scaling analysis of zircon populations shows that the Popo Agie samples are similar to other Upper Triassic units surrounding the Ancestral Uncompahgre Highlands, Central Colorado Trough, and the Ancestral Front Range. Additionally, we present the first maximum depositional ages (youngest population) for the Popo Agie Formation at a location where the top of the ochre unit is no older than 225 ± 4 Ma, and the upper purple to ochre transition is no older than 230 ± 5 Ma. By leveraging existing biostratigraphy, regional lithostratigraphy, and new radioisotopic ages we temporally constrain the Popo Agie Formation, enabling us to integrate the upper Chugwater Group, Chinle Formation, and Dockum Group strata into a testable Late Triassic chronostratigraphic framework for the western USA. The consilience of data support a Carnian age for the majority (if not entirety) of the Popo Agie Formation, making this—and equivalent strata in the Dockum Group (i.e., Camp Springs Conglomerate, and strata of the Tecolotito and Los Esteros members of the Santa Rosa Formation)—among the oldest continental Late Triassic stratigraphic units in the western USA.

A new fossil katydid of the genus Arethaea Stål (Orthoptera: Tettigoniidae) with exceptionally preserved internal organs from the Eocene Green River Formation of Colorado

Orthoptera (grasshoppers, crickets, and katydids) are abundant and diverse in the lower–middle Eocene Green River Formation of the Piceance Basin in northwestern Colorado, though remain almost entirely unstudied. Here, we describe a new species of the katydid genus Arethaea Stål (Tettigoniidae: Phaneropterinae: Insarini) from the Parachute Creek Member at a locality near Meeker in Rio Blanco County. Arethaea solterae Heads, Thomas & Hedlund sp. nov. is the first fossil member of the genus and the first tettigoniid described from the Green River Formation. The holotype and only known specimen is remarkable for the exceptional preservation of internal organs including the anterior midgut (ventriculus) and what appear to be a testis, accessory glands, and possible fat body.

Genetic mark–recapture analysis reveals large annual variation in pre‐breeding sex ratio of greater sage‐grouse

Sex ratio, and the extent to which it varies over time, is an important factor in the demography, management, and conservation of wildlife populations. Greater sage‐grouse Centrocercus urophasianus populations in western North America are monitored using counts of males at leks in spring. Population estimates derived from lek‐count data typically assume a constant, female‐biased sex ratio, yet few rigorous, empirically derived estimates of sex ratio are available to test that assumption. We estimated pre‐breeding sex ratio of greater sage‐grouse in a peripheral, geographically isolated population in northwestern Colorado during two consecutive winters using closed‐population, robust‐design, multi‐state, genetic mark–recapture models in program MARK. Sex ratio varied markedly between years, with estimates of 3.29 (95% CI: 2.36–4.59) females per male in winter 2012–2013 and 1.54 (95% CI: 1.22–1.95) females per male in winter 2013–2014. Rather than assuming a constant sex ratio, biologists should consider the potential for large annual variation in sex ratio of greater sage‐grouse populations when estimating population size or trend from male lek‐count data.

Structural control of Cambrian paleotopography and patterns of transgression in western Laurentia

Abstract The Cambrian transgression across the Great Unconformity produced one of the largest expansions of shallow marine habitats and associated diversification of marine invertebrate faunas in Earth history. However, identification of the underlying controls on the pattern of transgression of Cambrian seas has been hampered by imprecise or inaccurate age assignments for many formations. Recovery of an Ehmaniella Zone trilobite fauna from the Lodore Formation in northwestern Colorado (United States) revises the age of this unit to be significantly older, specifically middle Miaolingian (upper Wuliuan). This expands the established distribution of thick Miaolingian deposits of the northern Rocky Mountains to within 90 km of a broad region of central Colorado where Miaolingian strata are missing and Furongian successions rest directly on basement. The boundary between these two regions marks the position of an ~200 km east-west offset within the generally north-south–trending Cambrian paleoshoreline of western North America. The offset is co-located with a Precambrian continental suture zone (Cheyenne belt) at the northern Yavapai terrane margin and is directly east of an offset of similar magnitude and latitude in the early to middle Paleozoic shelf edge in Nevada. We thus posit that Precambrian deep-seated crustal-scale features controlled the Cambrian paleotopography of western Laurentia, strongly influencing the patterns of Cambrian transgression and structure of the shallow marine ecosystem established during continental submergence. These continental-scale structural elements remained a major control on marine paleogeography for >200 m.y. into the late Paleozoic.

Plant and mule deer responses to pinyon‐juniper removal by three mechanical methods

AbstractLand managers in western North America often reverse succession by removing pinyon (Pinus spp.) and juniper (Juniperus spp.) trees to reduce fire risk and increase forage for wildlife and livestock. Because prescribed fire carries inherent risks, mechanical methods such as chaining, roller‐chopping, and mastication are often used. Mechanical methods differ in cost and the size of woody debris produced, and may differentially impact plant and animal responses. We implemented a randomized, complete‐block, split‐plot experiment in December 2011 in the Piceance Basin, northwestern Colorado, USA, to compare mechanical methods and to explore seeding (subplot) interactions. We assessed vegetation 1‐, 2‐, 5‐, and 6‐years post‐treatment, and mule deer (Odocoileus hemionus) response via GPS locations 3–8 years post‐treatment. By 2016, treated plots had 3–5 times higher perennial grass cover and ~10 times higher cheatgrass (Bromus tectorum) cover than untreated control plots. Roller‐chopped plots had both the highest non‐native annual forb cover, and when seeded, the highest density of bitterbrush (Purshia tridentata), a nutritious shrub used by mule deer. Masticated plots had higher bitterbrush use during summer and fall, leaving less forage available for winter. Days of winter mule deer use from GPS point locations in chained and roller‐chopped plots was ~70% higher than in control plots, while winter use in masticated plots was similar to control plots. Mule deer use appears related to a combination of hiding cover, resulting from residual woody debris, and winter forage availability. Roller‐chopped plots provide the best combination of hiding cover and winter forage, but mastication or chaining, applied leaving dispersed security cover, may be better options at large scales or when invasive species concerns exist.

Simulating the source waters for the Wilkins Peak Member evaporite sequence with modern soda spring analogues

Chemical sediments of the lacustrine Wilkins Peak Member of the Eocene Green River Formation potentially preserve detailed paleoclimate information relating to the conditions of their formation and preservation within the lake basin during the Early Eocene Climatic Optimum. The Green River Formation comprises the world's largest sodium-carbonate evaporite deposit in the form of trona (Na2CO3⋅NaHCO3⋅2H2O) in the Bridger Basin and nahcolite (NaHCO3) in the neighboring Piceance Creek Basin. Modern analogues suggest that these minerals necessitate the existence of an alkaline source water. Detrital provenance geochronometers suggest that the most likely source for volcanic waters to the Greater Green River Basin is the Colorado Mineral Belt, connected to the basin via the Aspen paleoriver.Here, we test the hypothesis that magmatic waters from the Colorado Mineral Belt could have supplied the Greater Green River Basin with the alkalinity needed to precipitate sodium-carbonate evaporites that are preserved in the Wilkins Peak Member by numerically simulating the evaporation of modern soda spring waters from northwestern Colorado at various temperature and atmospheric pCO2 conditions. The resulting simulated evaporite sequence is then compared to the mineralogy and textures preserved within the Wilkins Peak Member. Simulated evaporation of Steamboat Springs and Mineral Spring waters produce a close match to core observations and mineralogy. These simulations provide constraints on the salinities at which various minerals precipitated in the Wilkins Peak Member as well as insights into the regional temperature (>15 °C for gaylussite and trona; >27° for pirssonite and trona) and pCO2 conditions (<1200 ppm for gaylussite and trona) during the Early Eocene Climatic Optimum.

A tyrannosaurid pedal ungual from the Williams Fork Formation (Campanian) of Colorado and its implications for the biogeography of Laramidian dinosaurs

A right theropod pedal ungual phalanx II-3 from the Campanian Williams Fork Formation of northwestern Colorado is described, and a combination of features, including the large size, tapering distal tip, robust and stout overall form, triangular cross-section, and a relatively flat ventral surface allows a confident referral to Tyrannosauridae Osborn, 1906. Although this specimen was found in a relatively southern state, the proximal articular surface of this ungual is similar to that of Gorgosaurus libratus Lambe, 1914, a taxon found in the northern state, Alberta. Although based on limited evidence, this may suggest that the range of tyrannosaurids considered endemic to the north of Laramidia extended farther south than previously thought.

Remote mapping of leafy spurge (Euphorbia esula, L.) in Northwestern Colorado

Leafy spurge (Euphorbia esula L.) has been introduced to the Yampa River in Northwestern Colorado for over 40 years and flood and runoff events transport leafy spurge propagules onto adjacent landscapes. The spread of leafy spurge beyond the river channels has yet to be mapped and recorded, and this research was conducted to map leafy spurge occurrence in the Yampa River Valley. Significant stakeholder mapping efforts took place in the summer of 2019–2021, leading to excellent spatial data on leafy spurge presence and absence along the main channel. In summer 2019, multispectral SPOT seven satellite imagery, stakeholder ground mapping efforts, and bright yellow-green leafy spurge bracts were used to interpret imagery, identify dense, unobscured patches of leafy spurge, and digitize them. Spectral signatures from training samples for leafy spurge and other land cover classes (generalized as “not leafy spurge”) were then used to train a Random Forest machine learning classification. In the summer of 2021, generated classification maps were compared to multispectral satellite imagery and stakeholder ground mapped leafy spurge presence. Mismatches were identified, and 271 validation locations were identified, navigated to, and evaluated for leafy spurge presence. Leafy spurge training samples were classified with 96% accuracy. Correctly classified leafy spurge locations had higher leafy spurge coverage and lower overstory canopy than missed leafy spurge locations. Leafy spurge growing beneath shrub canopy or growing as individual plants along the riverbanks were more likely to be missed. A frequency analysis for other plant species found at validation locations determined that smooth brome (Bromus inermis Leyss.), dandelion (Taraxacum officinale L.), and willow (Salix sp.) were most frequently misclassified as leafy spurge. In conclusion, multispectral satellite imagery was useful at remote detection of leafy spurge in open areas with dense leafy spurge coverage, but more work must be done for identification of sparse and diffuse leafy spurge infestations.

Columbian sharp‐tailed grouse female and nest survival in northwestern Colorado

AbstractWildlife management and conservation can be challenging when the demography of a focal species is unknown or limited given that fecundity and adult survival influence population growth. The Columbian sharp‐tailed grouse (Tympanuchus phasianellus columbianus) have been reduced to ≤10% of their former range since the early 1900s. We conducted a 3‐year study (2015–2017) across 4 study sites in northwestern Colorado, USA, to evaluate female hazard and nest survival. We trapped and marked 270 female sharp‐tailed grouse and identified 275 nests for our hazard and survival analyses. Females during the breeding stage of the reproductive season experienced more hazard compared to the nesting and the early and late post‐nesting stages for females without broods. Females experienced a higher degree of hazard during the breeding stage and mortality risk was &gt;3 times higher than the nesting stage, &gt;7 times higher than early post‐nesting (EPN)‐no brood stage, and &gt;5 times higher than the late post‐nesting (LPN)‐unsuccessful stage. Two reproductive season stages (LPN‐successful and EPN‐brood) provided marginal inference. Nest incubation initiation date and nest age best described nest daily survival. Females that initiated incubation of initial nests earlier in the season experienced lower nest daily survival than later in the incubation season. Because female Columbian sharp‐tailed grouse hazard varied among different reproductive season stages, we recommend that wildlife managers develop management actions that reduce hazard during the specific reproductive season stages (i.e., the breeding season). For Columbian sharp‐tailed grouse in Colorado, we recommend that Colorado Parks and Wildlife collaborate with federal farm program agencies to implement a no‐tillage restriction from 1 May through 30 June for active agricultural fields within 2 km of active Columbian sharp‐tailed grouse leks to enhance nest survival.

Survival of Columbian sharp‐tailed grouse chicks and juveniles in northwestern Colorado

AbstractChick and juvenile survival are important vital rates for population monitoring and making sound management decisions. These demographics are poorly understood in Columbian sharp‐tailed grouse (Tympanuchus phasianellus columbianus) and survival estimation in the first 2 weeks is particularly challenging to assess. In 2015–2017, we captured 1,219 chicks (1–7 days old) from 156 broods. We marked 625 chicks with radio‐transmitters to monitor their survival and recaptured them to replace the radio‐transmitter from 18–30 days old. Overall survival of chicks and juveniles for the brood‐rearing season (initial capture–31 Aug) was 0.30 ± 0.02 (SE; 95% CI = 0.26, 0.35, n = 746) using the Kaplan‐Meier product‐limit estimator. We used Cox proportional hazards regression to model survival and for chicks entering the study at 2–4 days old, survival to 21 days old was 0.59 ± 0.03 (95% CI = 0.53, 0.65, n = 529) and increasing chick mass had a positive effect on chick survival probability, with a 6.0% decrease in mortality risk for each additional gram of mass at initial capture. Juvenile survival was 0.51 ± 0.04 (95% CI = 0.43, 0.60, n = 294) and differed by study site. Of our 4 study sites, the 2 western sites (West Axial, Iles Dome) had 65–80% greater hazard compared to the 2 more eastern sites (Routt, Trapper). Juvenile survival was also influenced by hatch date, with a 3.0% greater hazard for each day later in the nesting season that a nest hatched. Because chick survival is positively influenced by greater mass at capture and juvenile survival was positively affected by earlier hatching dates of broods, management actions should focus on improving the habitat surrounding lek sites to increase the success of initial nests and to provide high quality (increased levels of calcium, phosphorus, and protein) and quantity forage to nesting females and chicks to increase survival and population stability. Additionally, given that lower mass increases the hazard for chick survival, researchers planning to mark chicks should not mark individuals &lt;11 g when using a 0.55‐g radio‐transmitter. Radio‐transmitters for chicks should not exceed 5.0% of the chicks' body mass at the time of marking.

The Clean Water Act and biosolids: A 45‐year chronological review of biosolids land application research in Colorado

The 1972 U.S. Clean Water Act set forth the generation of biosolids. In Colorado, biosolids land application research began in 1976 and continues today. Pastureland research suggested that sewage effluent could effectively be land applied to benefit aboveground plant growth and to polish water prior to reaching receiving waters. Forest wildfire-affected ecosystems can also benefit from biosolids applications; application rates of up to 80 Mg ha-1 can lead to greater plant establishment, soil microbial activity, and nutrient turnover and reduced nutrient and heavy metal concentrations in runoff below livestock and USEPA drinking water standards. Long-term (24-yr) observations in oil shale-mined lands showed that biosolids (up to 224 Mg ha-1 ) can have a positive effect on microbial-mediated nutrient cycling and, in turn, on aboveground plant community structure. Biosolids applications of up to 40 Mg ha-1 in high-elevation shrubland ecosystems, dominated by Mo-containing shale deposits, can aid in reducing imbalances between Mo and Cu in soils and plants; excessive plant Mo, when consumed by ruminants, can lead to molybdenosis. Biosolids and lime applications (both at 224 Mg ha-1 ) have been shown to improve long-term reclamation success on acid-generating, heavy metal-containing fluvial mine tailings. Thirty years of grazing land research, focused on soil and aboveground plant benefits, illustrate that soil health and plant productivity can be improved to the greatest extent at biosolids application rates close to 10 Mg ha-1 . Finally, 40 yr of dryland agroecosystem research (a) have helped identify biosolids N fertilizer equivalency (∼8kg N Mg-1 ) and thus dryland winter wheat application rates (e.g., 4.5-6.7 dry Mg ha-1 ); (b) have identified first-year mineralization rates of 25-32%; (c) dispute the "time bomb" theory by showing that plant metal uptake follows an exponential rise to a maximum; (d) showcase economic return to producers via increased wheat grain protein content; (e) suggest that biosolids-borne proteins and their degradation products are labile C and N sources; (f) have led to long-term tracking of micronutrients and heavy metals in soils and revealed that plants-soil concentrations will not lead to groundwater degradation and that plants are safe for human consumption; and (g) have shown that biosolids provide Zn, helping to overcome soil deficiencies and enhancing Zn biofortification in wheat grain. This latter point is important because ∼2 billion people globally suffer from Zn deficiencies. Forty-five years of research in Colorado have proven that biosolids can enhance environmental quality, improve soil health, and produce healthy food products.

Insights into the Devonian–Carboniferous transition and Hangenberg Event from δ13Ccarb and 87Sr/86Sr chemostratigraphy of shallow platform carbonate strata of northwestern Colorado

ABSTRACTPaired chemostratigraphic and biostratigraphic data suggest that the Devonian–Carboniferous boundary and the Hangenberg extinction event are recorded in the Coffee Pot Member of the Dyer Formation of the White River uplift region of northwestern Colorado. The Hangenberg isotopic excursion interval occurs in biostratigraphically depauperate shallow platform micritic dolostone and limestone representing the aculeatus–?ultimus–kockeli? Zone. The Hangenberg interval strata have δ13Ccarb values up to 7.69‰, and locally contain ooids, stromatolites, and other microbial structures. In three sections, there is a short-lived &amp;gt; 4‰ “pre-Hangenberg” positive excursion that is associated with the presence of detrital dolomite siltstone. The main Hangenberg isotopic signature exists in overlying strata, and is replicated in four different sections of the Dyer Formation across an area ~300 km2. In each section, the excursion interval is preceded by, and in one location is interrupted by, evidence of meteoric diagenesis and/or emergence characterized by macroscopic dissolution features and pronounced negative δ13Ccarb values (to ca. -6‰). Conodont 87Sr/86Sr ratios through the Dyer Formation dip to nearly 0.708 during the onset of the Hangenberg Event, consistent with the brachiopod based 87Sr/86Sr nadir from the same interval in Missouri, France, and Germany. The least-radiogenic trendline through the Dyer 87Sr/86Sr record matches the global minimum 87Sr/86Sr trendline through the Famennian–Tournaisian transition and infills several gaps in the global record.

The December 2021 Marshall Fire: Predictability and Gust Forecasts from Operational Models

We analyzed meteorological conditions that occurred during the December 2021 Boulder, Colorado, downslope windstorm. This event is of particular interest due to the ignition and spread of the Marshall Fire, which quickly became the most destructive wildfire in Colorado history. Observations indicated a rapid onset of fast winds with gusts as high as 51 m/s that generally remained confined to the east-facing slopes and foothills of the Rockies, similar to previous Boulder windstorms. After about 12 h, the windstorm shifted into a second, less intense phase. Midtropospheric winds above northwestern Colorado weakened prior to the onset of strong surface winds and the event strength started waning as stronger winds moved back into the area. Forecasts from NOAA high-resolution operational models initialized more than a few hours prior to windstorm onset did not simulate the start time, development rate and/or maximum strength of the windstorm correctly, and day-ahead runs even failed to develop strong downslope windstorms at all. Idealized modeling confirmed that predictability was limited by errors on the synoptic scale affecting the midtropospheric wind conditions representing the Boulder windstorm’s inflow environment. Gust forecasts for this event were critically evaluated.

The Upper Cretaceous Rock Springs Formation of northwest Colorado

The Upper Cretaceous Rock Springs Formation of the Mesaverde Group in northwestern Colorado, southwestern Wyoming, and northeastern Utah is composed of fluvial, deltaic, and marine sediments that record the regression of the Western Interior Seaway during the Early to Middle Campanian. Contemporaneous deposits are present along the eastern and southeastern margins of the Greater Green River Basin in Wyoming, but correlation across the basin is challenging. Analysis of a small (1-km-long), understudied outcrop in northwestern Colorado assists in bridging that gap. The outcrop consists of distal and proximal deltaic deposits, overlain by distributary-channel complexes within delta-plain deposits. Correlation panels based on subsurface wireline logs and outcrop gamma-ray profiles show that the deposits are younger than lithostratigraphically equivalent strata of the Rock Springs Formation in Utah and Wyoming. Regional nomenclature is introduced for the area, and it is shown that these deposits differ from better-documented, older Rock Springs Formation deposits in Utah and Wyoming by having a higher net sandstone percentage due to the presence of substantial distributary-channel complexes. This study benefits subsurface exploration efforts in the Greater Green River Basin by providing outcrop analogs of reservoir distribution and quality.

New Upper Cretaceous Microvertebrate Assemblage from the Williams Fork Formation, northwestern Colorado, U.S.A., and its Paleoenvironmental Implications

New Upper Cretaceous Microvertebrate Assemblage from the Williams Fork Formation, northwestern Colorado, U.S.A., and its Paleoenvironmental Implications

Conodonts and the Devonian–Carboniferous transition in the Dyer Formation, Colorado

ABSTRACT Conodont assemblages from shallow platform carbonate strata of the Dyer Formation in northwestern Colorado indicate that the unit spans the Devonian–Carboniferous transition, and include four new taxa, described herein. The underlying Parting Formation and most of the Broken Rib Member of the Dyer Formation are in the Palmatolepis expansa Zone. The upper portion of the Broken Rib Member and the lower part of the Coffee Pot Member of the Dyer Formation are in the Bispathodus aculeatus Zone to the Bispathodus ultimus Zone, and associated with an ~6‰ positive δ13C shift identified as the end-Devonian Hangenberg excursion. Upper Coffee Pot Member conodonts are equivocally Tournaisian, and cap the δ13C excursion. Collectively, these observations suggest that the Devonian–Carboniferous boundary is in the upper Coffee Pot Member of the Dyer Formation, and thus the overlying Gilman Sandstone is Carboniferous.

A near-range plant invasion homogenizes riparian vegetation but leads to more productive bird communities

AbstractBiological invasions are a leading driver of biodiversity loss and population declines worldwide. While much research has focused on understanding the effects of long-distance (e.g., cross-continental) invasion, the potential impacts of species that invade close to or within their native ranges are relatively understudied. We investigated the effects of the near-range introduction of a non-native plant, New Mexico locust (Robinia neomexicana), on riparian plant and bird communities in northwestern Colorado, USA. By surveying plant and bird communities and examining nest success and productivity in riparian forest with and without locust, we evaluated the following ecological responses to invasion: (1) tree and shrub richness and density; (2) bird species richness, occupancy, and abundance; and (3) avian reproductive success. Our results demonstrate biotic homogenization of the plant community with increasing intensity of locust invasion, yet we found little evidence for negative effects on avian habitat use or reproductive success. Instead, locust invasion showed a positive effect on nest productivity, with significantly higher brood sizes and numbers of young fledged for nests in invaded habitats compared to those where locust was absent. Because climate change is already leading to shifts in species distribution patterns, we suggest that understanding the ecological consequences of plant invasions that occur within or near historic ranges will advance the science and practice of invasive species biology in a changing world. Our findings of mostly neutral to positive effects of locust suggest that near-range plant invasions may not always negatively impact community structure.

Business as usual: macrolichen community response to the resilience of spruce–fir forests to beetle disturbance in northwestern Colorado

Over the past few decades, spruce beetles (Dendroctonus rufipennis Kirby) have drastically altered spruce–fir forests in western North America. Past research has shown that forest conditions (i.e., canopy openings, amounts of coarse woody material) change after spruce beetle disturbance, but little work has studied the impacts of these changes on the resident biotic communities. Even less research has investigated how spruce beetle disturbance affects lichen communities, which we anticipated as benefiting them due to canopy opening and increased woody material availability. We studied macrolichen community structure, including abundance and community composition, and habitat characteristics in areas with significant spruce beetle damage, as first detected between 1996 and 2017 in northwestern Colorado. We found few habitat differences among beetle disturbance classes that reflected varying time since infestation, and only the most recently affected plots (2012–2017) had significantly different lichen community structure relative to other sampled areas. We observed that the spruce–fir forests within our study exhibited ecological resilience to beetle outbreaks, and we did not measure differences in the amount of canopy openings or amounts of coarse woody material. Subsequently, the lack of differential lichen community response was not surprising.

Evaluation of the integrated riparian ecosystem response to future flow regimes on semiarid rivers in Colorado, USA

Riparian ecosystems are shaped by interactions among streamflow, plants, and physical processes. Sustaining functioning riparian ecosystems in the face of climate change, growing human demands for water, and increasing water scarcity requires improved understanding of the sensitivity of riparian ecosystems to shifts in flow regimes and associated adaptive management strategies. We applied projected future flow regimes to an ecogeomorphic model of riparian and channel response to evaluate these interactions. We tested the hypothesis that components of the riparian ecosystem vary in their vulnerabilities to shifts in flow attributes and that changes in the representation of functional groups of plants result from interactions between ecological and physical drivers. Using the Yampa and Green Rivers in northwestern Colorado as our test system, we investigated ecogeomorphic response to (1) synthetic flow regimes representing continuous changes from baseline flows; and (2) future flow scenarios that incorporate changing climate, demand, and water-resource projects. For this region, we showed that riparian plant presence, composition, and cover are highly sensitive to the high flows that occur early in the growing season, but that shifts to low flows are also important, especially for determining the functional diversity of a riparian community. Future flow regimes are likely to induce vegetation encroachment on lower channel surfaces and to increase plant cover, which will be dominated by fewer functional groups. In particular, we predict a decrease in some mesic plants (shrubs and tall herbs) and an increase in presence and cover of late-seral, xeric shrubs, most of which are non-native species. Managing for high flows that occur early in the growing season must complement maintenance of adequate baseflows to maintain ecosystem functioning in the face of hydrologic alterations induced by climate change and human water demand.