Southern Rocky Research Articles

Characterization of Foliar Fungal Endophyte Communities from White Pine Blister Rust Resistant and Susceptible Pinus flexilis in Natural Stands in the Southern Rocky Mountains

Fungal endophytic communities in needles of field-grown Pinus flexilis previously inferred to carry major gene resistance (R) to white pine blister rust (WPBR) or to lack it (S) were surveyed to identify unique microbes that may be recruited by WPBR-resistant genotypes. Resistant and susceptible trees were sampled in each of 11 P. flexilis populations for a total of 50 trees sampled. Through next-generation sequencing, this study showed a diverse needle mycobiota in P. flexilis, of which many remain unknown, regardless of the presence or absence of the WPBR resistance gene, Cr4. Ascomycota dominated the mycobiota (88.9%) followed by Basidiomycota (4.4%) and Chytridiomycota (0.03%), and the remaining 6.7% were unclassified. Shared ( n = 105) and unique ( n = 48 in R and n = 49 in S) fungal taxa, including differentially abundant operational taxonomic units, were identified that could provide insights into core mycobiota and host genotype-specific fungal groups. Marginal variation of the fungal diversity and structure was observed between host genotypes, which indicates that neither Cr4 nor the physiological differences associated with the presence or absence of the gene affects mycobiota recruitment. Instead, other parameters, including host size (diameter at breast height) and site elevation, significantly influenced the variability of the composition and structure of the fungal endophytic community. Further investigations are needed to understand the relationship of unique or differentially abundant taxa with one genotype or the other, and to determine the role of the needle mycobiota in WPBR disease development in natural stands of P. flexilis.

Increasing wildfire impacts on snowpack in the western U.S.

Wildfire area has been increasing in most ecoregions across the western United States, including snow-dominated regions. These fires modify snow accumulation, ablation, and duration, but the sign and magnitude of these impacts can vary substantially between regions. This study compares spatiotemporal patterns of western United States wildfires between ecoregions and snow zones. Results demonstrate significant increases in wildfire area from 1984 to 2020 throughout the West, including the Sierra Nevada, Cascades, Basin and Range, and Northern to Southern Rockies. In the late snow zone, where mean annual snow-free date is in May or later, 70% of ecoregions experienced significant increases in wildfire area since 1984. The distribution of burned area shifted from earlier melt zones to later-melt snow zones in several ecoregions, including the Southern Rockies, where the area burned in the late snow zone during 2020 exceeded the total burned area over the previous 36 y combined. Snow measurements at a large Southern Rockies fire revealed that burning caused lower magnitude and earlier peak snow-water equivalent as well as an 18-24 d estimated advance in snow-free dates. Latitude, a proxy for solar radiation, is a dominant driver of snow-free date, and fire advances snow-free timing through a more-positive net shortwave radiation balance. This loss of snow can reduce both ecosystem water availability and streamflow generation in a region that relies heavily on mountain snowpack for water supply.

Responses of vegetation to changes in terrestrial water storage and temperature in global mountainous regions

As an important component of terrestrial ecosystem, vegetation acts as a sensitive recorder of changes in hydroclimatic conditions. Long-term time series of remote sensing-based vegetation indices and their influencing environmental driving factors, such as human activities and climate change, have been widely discussed in the literature. Globally, however, little is known about the hydroclimatic processes controlling vegetation changes in mountainous regions, which are conceived as more sensitive to climate change than other landscapes. The present study aims to quantify the respective roles of two dominant hydroclimatic factors, namely, TWS (i.e., terrestrial water storage) and Tair (i.e., temperature), in the spatio-temporal changes of mountainous vegetation over global six contrasting climate zones (i.e., tropical, arid, subtropical, temperate, sub-frigid, and frigid zones) during the period 2003–2016 based on EVI (i.e., enhanced vegetation index), TWS, Tair, and elevation data. Results indicate that the mean EVI shows a larger increasing trend (+0.85 %/decade, p-value < 0.01) and a larger decreasing trend in TWS (−85 mm/decade, p-value < 0.01) across the global mountainous regions than other global regions combined together (+0.61 %/decade, p-value < 0.01), particularly over high latitudes. With the increasing latitudes, the positive effect of temperature more dominates mountainous vegetation growth than moisture, as evidenced by the increasing trends of EVI with warming. However, in certain low-latitude mountainous regions (e.g., East Africa, South Asia, the western Tibetan Plateau, Brazil Plateau, and the southern Rocky Mountains), mountainous vegetation may face degradation due to water deficit induced by increased snowmelt, especially among the high-elevation ecosystems. The water availability controls vegetation activities more than Tair in the mid- and low-latitude regions, including the tropical, arid, and subtropical climate zones. These findings indicate that the potential shifts in mountainous vegetation may occur under the notable interactions with hydroclimatic factors, as the high-latitudes are experiencing ongoing warming and the mid- and low-latitudes are getting dryer.

Trichomycetes from the Columbia Mountains, British Columbia, Canada

Trichomycetes are a group of fungi and protists living in the guts of immature aquatic insects and other arthropods. The nature of this relationship is poorly understood but it is mostly described as obligately commensalistic, with the microbes exploiting a unique microhabitat. Collections of trichomycetes were made from freshwater insects in aquatic habitats near Castlegar in the Columbia Mountains, part of the Rocky Mountain Range in southeastern British Columbia. The collection sites were at altitudes ranging from 435 to 935 m and were made in July 2006. A total of 32 species were recorded including four new species, Harpella filispora sp. nov., Orphella columbiensis sp. nov., Smittium nodiradicatum sp. nov., and Smitium basiangustatum sp. nov. described here. These are the first records from Western Canada and two, Austrosmittium patagonicum and Glotzia distorta are new continental records. These findings are compared to reports from the western edge of the Rocky Mountain range near the Boise Mountains in Idaho and the Southern Rockies in Colorado.

Floristic survey of the Sangre de Cristo Wilderness and environs (Colorado, U.S.A.)

The Sangre de Cristo Wilderness Area with its 226,445 acres is the third largest Wilderness Area in Colorado. It spans areas of the northern Sangre de Cristo Range in the southern Rocky Mountains, with elevations extending from 8,000 to 14,000 feet and vegetation ranging from piñon/juniper woodlands to alpine tundra.&#x0D; Over 7,000 vouchered specimens largely housed at the Rocky Mountain Herbarium in Laramie, Wyoming (RM) [4,322], and the University of Colorado Herbarium in Boulder, Colorado (COLO) [2,133] were consulted for report. Seven hundred twenty (720) taxa are reported from the study area, with 75 families and 310 genera represented. Predominantly a Western North American flora 40.6% with 292 spp., it is followed by 13.1% of the taxa being native to North America with 94 spp. The Southern Rockies contribute an additional 13.1% with 94 spp. (10 of these taxa being restricted to Colorado). Fifteen species fully tracked by the Colorado Natural Heritage Program (CNHP 2011) were documented from the study area with four of these considered globally imperiled (G1 or G2) with the majority of these having an alpine distribution. Non-native species accounted for 4.0% of the flora (29 spp.), a reflection of the high elevation environment and wilderness qualities of the region. There are no species listed as threatened or endangered under the Endangered Species Act in the area.

Revisiting talus and free-air temperatures after 50 years of change at an American pika (Ochotona princeps) study site in the Southern Rockies

Climate change in mountain regions has exposed high-elevation species to rapidly changing temperatures. Although climate exposure can be reduced in certain microclimates, the quality of microclimatic refugia might also degrade with climate change. The American pika (Ochotona princeps) often inhabits high elevations, and is considered climate-sensitive due to its narrow thermal tolerance and recent extirpations in some warmer portions of its range. Pikas behaviorally thermoregulate by taking refuge in the subsurface microclimates found in taluses and other rocky habitats, where daily thermal fluctuations are attenuated and somewhat decoupled from free-air temperatures. Changes in microclimate might reduce the efficacy of this behavioral thermoregulation. This study compares recent (2009–2021) subsurface temperatures at a long-term pika study site with a rare instance of historical (1963–1964) data from the same location. We also place historical and recent microclimates in context using long-term data on free-air temperatures from the same area. Recent free-air temperatures were often warmer than historical records, and subsurface temperatures exhibited even stronger warming between periods. Temperatures measured in the talus were often dramatically warmer in recent records, especially at the deeper of two subsurface sensor placements in this study. Winter months showed the greatest changes in both talus and free-air temperatures. Differences between historical and recent microclimates were not explained by the precise placement of sensors, as recent temperatures were similar across a wide variety of subsurface placements, and temporal changes in free-air temperatures at the historical study site were also reflected in data from nearby weather stations. Together, these results suggest that subsurface microclimates important for pika thermoregulation have changed over the past few decades, perhaps even faster than observed changes in free-air temperatures. The generality of these results and their potential ramifications for ecosystem processes and services should be explored.

Fire and ice: Winter flooding in a Southern Rocky Mountain stream after a wildfire

We observed a low-discharge flooding phenomenon on Little Beaver Creek, a tributary to the Cache la Poudre River in the Southern Rocky Mountains of Colorado, USA. Ice ranging in thickness from a few centimeters to 0.5 m occupied a large volume of the channel, forcing flows out of its banks. On two occasions, multiple consecutive days of uncharacteristically warm weather caused a spike in snowmelt, and bankfull stage was surpassed 60 days before peak runoff. The flow events occurred in late winter, six months after a wildfire had burned a large portion of the watershed at medium-to-high severity. Ash and other organic materials were mobilized during the overbank flows, and we observed evidence of recent ash deposition in the floodplain and high ash concentrations in the channel. During the same time period, camera footage captured the formation and collapse of a large accumulation of ice and snow at a log jam. Because climate change projections and recent observations indicate higher variability in weather patterns, wildfire regime, and precipitation events, winter flooding associated with ice, although not widely documented in small mountain streams, may become more common. Flooding and subsequent deposition of ash and other sediment can disrupt fluvial processes, impair the local biotic community, cause property damage, and impact drinking water sources.

Hybrid enrichment of adaptive variation revealed by genotype-environment associations in montane sedges.

The role of hybridization in diversification is complex and may result in many possible outcomes. Not only can hybridization produce new lineages, but those lineages may contain unique combinations of adaptive genetic variation derived from parental taxa that allow hybrid‐origin lineages to occupy unique environmental space relative to one (or both) parent(s). We document such a case of hybridization between two sedge species, Carex nova and Carex nelsonii (Cyperaceae), that occupy partially overlapping environmental space in the southern Rocky Mountains, USA. In the region hypothesized to be the origin of the hybrid lineage, one parental taxon (C. nelsonii) is at the edge of its environmental tolerance. Hybrid‐origin individuals display mixed ancestry between the parental taxa—of nearly 7000 unlinked loci sampled, almost 30% showed evidence of excess ancestry from one parental lineage—approximately half displayed a genomic background skewed towards one parent, and half skewed towards the other. To test whether excess ancestry loci may have conferred an adaptive advantage to the hybrid‐origin lineage, we conducted genotype–environment association analyses on different combinations of loci—with and without excess ancestry—and with multiple contrasts between the hybrids and parental taxa. Loci with skewed ancestry showed significant environmental associations distinguishing the hybrid lineage from one parent (C. nelsonii), whereas loci with relatively equal representation of parental ancestries showed no such environmental associations. Moreover, the overwhelming majority of candidate adaptive loci with respect to environmental gradients also had excess ancestry from a parental lineage, implying these loci have facilitated the persistence of the hybrid lineage in an environment unsuitable to at least one parent.

Expression of the “4.2 ka event” in the southern Rocky Mountains, USA

Abstract. The use of the climatic anomaly known as the “4.2 ka event” as the stratigraphic division between the middle and late Holocene has prompted debate over its impact, geographic pattern, and significance. The anomaly has primarily been described as abrupt drying in the Northern Hemisphere at ca. 4 ka (ka, thousands of years before present), but evidence of the hydroclimate change is inconsistent among sites both globally and within North America. Climate records from the southern Rocky Mountains demonstrate the challenge with diagnosing the extent and severity of the anomaly. Dune-field chronologies and a pollen record in southeastern Wyoming reveal several centuries of low moisture at around 4.2 ka, and prominent low stands in lakes in Colorado suggest the drought was unique amid Holocene variability, but detailed carbonate oxygen isotope (δ18Ocarb) records from Colorado do not record drought at the same time. We find new evidence from δ18Ocarb in a small mountain lake in southeastern Wyoming of an abrupt reduction in effective moisture or snowpack from approximately 4.2–4 ka, which coincides in time with the other evidence of regional drying from the southern Rocky Mountains and the western Great Plains. We find that the δ18Ocarb in our record may reflect cool-season inputs into the lake, which do not appear to track the strong enrichment of heavy oxygen by evaporation during summer months today. The modern relationship differs from some widely applied conceptual models of lake–isotope systems and may indicate reduced winter precipitation rather than enhanced evaporation at ca. 4.2 ka. Inconsistencies among the North American records, particularly in δ18Ocarb trends, thus show that site-specific factors can prevent identification of the patterns of multi-century drought. However, the prominence of the drought at ca. 4 ka among a growing number of sites in the North American interior suggests it was a regionally substantial climate event amid other Holocene variability.

Simplified Cross‐Validation in Principal Component Regression (PCR) and PCR‐Like Machine Learning for Water Supply Forecasting

AbstractCross‐validated principal component regression (PCR) is widely used in day‐to‐day operational forecasting systems for seasonal river runoff volume in western North America. Complexities are increasing in both predictor datasets (including climate‐science products) and in predictive models employed instead of linear regression within the PCR framework (including artificial intelligence), potentially complicating cross‐validation for model evaluation. We explored these issues with 300 modeling experiments on two high‐impact and hydroclimatically diverse basins in the western United States, the Truckee River (Sierra Nevada) and Rio Grande headwaters (southern Rockies), using five different PCR and PCR‐like machine learning models. The results suggest out‐of‐sample error is satisfactorily estimated by applying cross‐validation to only the final, supervised learning, step of PCR/PCR‐like procedures. The outcome facilitates streamlined algorithms and potentially reduced computational times for more complex emerging model architectures and datasets; provides reassurance around a possible inability to perform genuinely complete cross‐validation when predictors include certain complex and externally sourced data sources; and may reflect mitigation of overtraining by geophysical process‐informed model development protocols normally used during feature selection in operational water supply forecast (WSF). The results provide practical guidance helping support the design of next‐generation WSF models.

Late Cretaceous time-transgressive onset of Laramide arch exhumation and basin subsidence across northern Arizona–New Mexico, USA, and the role of a dehydrating Farallon flat slab

Abstract Spatiotemporal constraints for Late Cretaceous tectonism across the Colorado Plateau and southern Rocky Mountains (northern Arizona–New Mexico, USA) are interpreted in regards to Laramide orogenic mechanisms. Onset of Laramide arch development is estimated from cooling recorded in representative thermochronologic samples in a three-step process of initial forward models, secondary HeFTy inverse models with informed constraint boxes, and a custom script to statistically estimate timing of rapid cooling from inverse model results. Onset of Laramide basin development is interpreted from increased rates of tectonic subsidence. Onset estimates are compared to published estimates for Laramide timing, and together suggest tectonism commenced ca. 90 Ma in northwestern Arizona and progressed eastward with later onset in northcentral New Mexico by ca. 75–70 Ma. The interpreted sweep of onset progressed at a rate of ∼50 km/m.y. and was approximately half the 100–150 km/m.y. rate estimated for Late Cretaceous Farallon-North America convergence during the same timeframe. Previous suggestions that the Laramide tectonic front progressed at a rate similar to convergence via basal traction are not supported by our results. We thereby suggest that (1) a plate margin end load established far field compression and that (2) sequential Laramide-style strain was facilitated by progressive weakening of North American lithosphere from the dehydrating Farallon flat slab. Results are compared to models of sweeping tectonism and magmatism in other parts of the Laramide foreland. Discussions of the utility of the custom script and the potential for stratigraphic constraints to represent only minimum onset estimates are also presented.

Post-Laramide, Eocene epeirogeny in central Colorado—The result of a mantle drip?

Abstract The Southern Rocky Mountains first rose during the Laramide Orogeny (ca. 75–45 Ma), but today's mountains and adjacent Great Plains owe their current height to later epeirogenic surface uplift. When and why epeirogeny affected the region are controversial. Sedimentation histories in two central Colorado basins, the South Park–High Park and Denver basins, shifted at 56–54 Ma from an orogenic to an epeirogenic pattern, suggesting central Colorado experienced epeirogeny at that time. To interrogate that hypothesis, we analyzed thermal histories for seven samples from central Colorado's Arkansas Hills and High Park using thermochronometers with closure temperatures below ~180 °C, enabling us to track sample exhumation from ~5–7 km depth. Three samples are from the Cretaceous Whitehorn pluton, and four are Precambrian granitoids. All zircon and titanite (U-Th)/He dates (ZHe and THe) and one apatite fission-track (AFT) date are similar to the 67 Ma pluton emplacement age. Whitehorn dates using the lower-temperature apatite (U-Th)/He (AHe) thermochronometer are 55–41 Ma. These data require two exhumation episodes, one ca. 67–60 Ma, the second beginning at 54–46 Ma. The pluton reached the surface by 37 Ma, based on the age of volcanic tuff filling a pluton-cutting paleovalley. The Precambrian samples do not further refine this thermal history owing to the comparatively higher He closure temperature of their more radiation-damaged apatite. Laramide crustal shortening caused 67–60 Ma exhumation. Arkansas Hills shortening ended before 67 Ma, so shortening could not have caused the exhumation event that began 54–46 Ma; thermochronology supports the Eocene epeirogeny hypothesis. Epeirogeny affected &amp;gt;2.0 × 104 km2, from the Sawatch Range to the Denver Basin. We attribute epeirogeny to an Eocene mantle drip that likely triggered subsequent drips, causing younger exhumation events in adjacent areas.

Early incubation and prolonged maturation of large ignimbrite magma bodies: Evidence from the Southern Rocky Mountain volcanic field, Colorado, USA

Abstract Clusters of early central volcanoes in the mid-Cenozoic Southern Rocky Mountain volcanic field (SRMVF; southwestern Colorado, USA) record sites of initial magmatic focusing that led to assembly of sizable upper-crustal magma bodies capable of generating large ignimbrites. Peak growth at precursor andesitic volcanoes was followed by extended periods (0.5 to &amp;gt;2 m.y.) of reduced eruptive activity during inferred prolonged incubation of the crustal reservoir prior to eruption of ignimbrites at the San Juan magmatic locus, as exemplified by the 5000 km3 Fish Canyon Tuff and associated La Garita caldera. After a magma system became thermally mature and compositionally evolved, additional large ignimbrites could erupt more rapidly from polycyclic calderas. In contrast, incubation times for smaller ignimbrite magmas, as at Crater Lake, Oregon, were briefer than for San Juan systems. Plutonic counterparts to the temporal-compositional assembly of arc-ignimbrite magmas are exemplified by incrementally emplaced granitoid intrusions like the Mesozoic Tuolumne complex in the Sierra Nevada.

The Transience of Channel‐Spanning Logjams in Mountain Streams

AbstractWe use 11 years of annual surveys in streams of the Southern Rockies of Colorado, USA, to examine the persistence and geomorphic effects of logjams. Each year’s survey includes ∼300 logjams along more than 21 km of four mountain streams in primarily old‐growth subalpine forest. Streams alternate longitudinally between laterally confined reaches with a single channel and wider reaches with multithread‐channel planform. We distinguish logjam persistence and site persistence. Logjam persistence is the median timespan over which an individual jam is present. Site persistence describes the tendency for jams to disappear and then re‐form at the same site. We hypothesize that (a) site persistence is greatest in multithread reaches, (b) logjam persistence is greatest in multithread reaches, and (c) average backwater storage at each jam is greater in multithread reaches. We find that spatial and temporal metrics of site persistence differ significantly between single and multithread reaches. Individual logjam persistence does not differ significantly. Backwater storage is significantly greater in multithread reaches. Varying combinations of riparian forest age and average logjams per channel length explain variation in jam and site persistence and backwater storage via multivariate linear regression analyses. Over the 11 years of survey, a total of 429 distinct logjams were observed. Only 2.1% of the population was present for all 11 annual surveys. Median jam persistence is 1–2.5 years; median site persistence is 6–10 years. Despite the transience of most channel‐spanning logjams in the population, these jams create persistent effects in channel planform and backwater storage.

El cambio climático afectará la distribución del búho manchado mexicano (Strix occidentalis lucida Nelson 1903)

Introducción: El búho manchado mexicano (Strix occidentalis lucida Nelson 1903) es una subespecie amenazada por la destrucción del hábitat y sensible al cambio climático. Esta se distribuye en los bosques maduros de Estados Unidos y México. Objetivo: Determinar la distribución potencial histórica (1970-2000) y futura (2021-2040, 2041- 2060 y 2061-2080) del búho manchado mexicano bajo dos escenarios de cambio climático (SSP 245 y SSP 585). Materiales y métodos: La distribución potencial se modeló con el software R, utilizando el algoritmo MaxEnt, 155 registros de presencia geográficamente no correlacionados y cinco capas bioclimáticas. Las áreas de idoneidad ambiental se predijeron para ocho unidades de manejo ambiental de Estados Unidos y México. Resultados y discusión: Tres variables de temperatura contribuyeron en 93.1 % a la predicción del modelo: rango diurno medio (44.8 %), temperatura máxima del mes más cálido (28.8 %) y promedio del trimestre más frío (19.5 %). Los escenarios futuros mostraron pérdidas paulatinas y continuas de espacio bioclimático idóneo para el ave en siete unidades de manejo, especialmente en el escenario de altas emisiones (SSP 585) en la Sierra Madre Oriental de México (-56.1 a -96.4 %). La unidad de manejo ambiental Montañas Rocosas del Sur, en Estados Unidos, fue la única que ganó espacio bioclimático idóneo (51.3 a 167.2 %) en todos los periodos. Conclusión: Aunque los cambios no son significativos, la pérdida de áreas de idoneidad bioclimática inicia en el 2030 e incrementa en el 2041 y, por tanto, el cambio climático representa una amenaza actual para esta ave rapaz.

The Influence of Burn Severity on Post-Fire Spectral Recovery of Three Fires in the Southern Rocky Mountains

Increased wildfire activity and altered post-fire climate in the Southern Rocky Mountains has the potential to influence forest resilience. The Southern Rocky Mountains are a leading edge of climate change and have experienced record-breaking fires in recent years. The change in post-fire regeneration and forest resilience could potentially include future ecological trajectories. In this paper, we examined patterns of post-fire spectral recovery using Landsat time series. Additionally, we utilized random forest models to analyze the impact of climate and burn severity on three fire events in the Southern Rocky Mountains. Fifteen years following the fires, none of the burned stands fully recovered to their pre-fire spectral states. The results suggested that burn severity significantly impacted post-fire spectral recovery, but that influence may decrease as time since fire increases. The biggest difference in forest recovery was among fire events, indicating that post-fire climate may be influential in post-fire recovery. The mean and minimum growing-season temperatures were more significant to post-fire recovery than the variability in precipitation, which is consistent with field-based analysis. The present study indicated that, as warming continues, there may be changes in forest density where forests are not regenerating to their pre-fire spectral states. Additionally, this study emphasizes how high-elevation forests continue to regenerate after fires, but that regeneration is markedly affected by post-fire climate.

Understory plant species and community changes following a mountain pine beetle outbreak in Rocky Mountain National Park, USA

AbstractAimsThe response of understory plants is an important, yet understudied element of forest dynamics associated with mountain pine beetle (MPB) disturbance. Here, we provide a detailed assessment of both the changes in understory species and communities over a 5‐year period following severe MPB‐induced lodgepole pine mortality. Specifically, we examine species turnover, rarity and mobility over time, and evaluate shifts in community composition, including the potential for post‐outbreak community homogenization or differentiation.LocationWestern Rocky Mountain National Park in the southern Rocky Mountains, Colorado.MethodsWe collected species occurrence data across lodgepole pine‐dominated forest understories using repeated sampling of the same study sites (during the peak of MPB activity and 5 years after).ResultsMore species appeared than disappeared 5 years after the peak of the outbreak. New species were comprised of both early‐ and late‐successional species, suggesting the presence of rather high microhabitat heterogeneity. Although most species remained relatively rare, the number of exceedingly rare species decreased, and the number of highly common species increased. Several species were able to take advantage of the new stand conditions and expand throughout the study area. Some species appeared to spread locally over short distances mainly via vegetative reproduction, others expanded primarily upwards in elevation, probably through long‐distance dispersal and some spread over both short and long distances. Non‐native species doubled in occurrence and tended to spread upslope, towards the interior of the park, yet remained a small component of the understory overall. Shifts in community composition were minimal, but a slight convergence of plant community groups suggests a trend towards community homogenization.ConclusionsOur results demonstrate that even relatively sparse and depauperate lodgepole pine forest understories may be altered in diverse ways following MPB‐induced overstory mortality, depending on the unique ability of species to respond to changes in site conditions and resource availability.

Outbreaks of Douglas-Fir Beetle Follow Western Spruce Budworm Defoliation in the Southern Rocky Mountains, USA

Changes in climate are altering disturbance regimes in forests of western North America, leading to increases in the potential for disturbance events to overlap in time and space. Though interactions between abiotic and biotic disturbance (e.g., the effect of bark beetle outbreak on subsequent wildfire) have been widely studied, interactions between multiple biotic disturbances are poorly understood. Defoliating insects, such as the western spruce budworm (WSB; Choristoneura freemanni), have been widely suggested to predispose trees to secondary colonization by bark beetles, such as the Douglas-fir beetle (DFB; Dendroctonus pseudotsugae). However, there is little quantitative research that supports this observation. Here, we asked: Does previous WSB damage increase the likelihood of subsequent DFB outbreak in Douglas-fir (Pseudotsuga menziesii) forests of the Southern Rocky Mountains, USA? To quantify areas affected by WSB and then DFB, we analyzed Aerial Detection Survey data from 1999–2019. We found that a DFB presence followed WSB defoliation more often than expected under a null model (i.e., random distribution). With climate change expected to intensify some biotic disturbances, an understanding of the interactions between insect outbreaks is important for forest management planning, as well as for improving our understanding of forest change.

Phylogenomics of paleoendemic lampshade spiders (Araneae, Hypochilidae, Hypochilus), with the description of a new species from montane California.

Hypochilus is a relictual lineage of Nearctic spiders distributed disjunctly across the United States in three montane regions (California, southern Rocky Mountains, southern Appalachia). Phylogenetic resolution of species relationships in Hypochilus has been challenging, and conserved morphology coupled with extreme genetic divergence has led to uncertain species limits in some complexes. Here, Hypochilus interspecies relationships have been reconstructed and cryptic speciation more critically evaluated using a combination of ultraconserved elements, mitochondrial CO1 by-catch, and morphology. Phylogenomic data strongly support the monophyly of regional clades and support a ((California, Appalachia), southern Rocky Mountains) topology. In Appalachia, five species are resolved as four lineages (H.thorelli Marx, 1888 and H.coylei Platnick, 1987 are clearly sister taxa), but the interrelationships of these four lineages remain unresolved. The Appalachian species H.pococki Platnick, 1987 is recovered as monophyletic but is highly genetically structured at the nuclear level. While algorithmic analyses of nuclear data indicate many species (e.g., all H.pococki populations as species), male morphology instead reveals striking stasis. Within the California clade, nuclear and mitochondrial lineages of H.petrunkevitchi Gertsch, 1958 correspond directly to drainage basins of the southern Sierra Nevada, with H.bernardino Catley, 1994 nested within H.petrunkevitchi and sister to the southernmost basin populations. Combining nuclear, mitochondrial, geographical, and morphological evidence a new species from the Tule River and Cedar Creek drainages is described, Hypochilusxomotesp. nov. We also emphasize the conservation issues that face several microendemic, habitat-specialized species in this remarkable genus.

Logjam fluctuations during the decade after a major blowdown along a mountain stream in the US Southern Rockies

AbstractA blowdown in 2011 along a 1200‐m length of Glacier Creek in the Southern Rockies of Colorado, USA substantially increased the number of channel‐spanning logjams and initiated formation of a 100‐m‐long multithread channel segment. Annual logjam surveys during 2012–2020 indicate that these effects have persisted for a decade, with the number of logjams remaining high despite inter‐annual variations in the location of individual jams. No single logjam has remained in place continuously since the blowdown, but logjams tend to persist longest and to re‐form at sites with large ramp pieces from one or both sides of the channel and a lateral constriction created by bedrock or large boulders that can buttress the ramped piece(s) downstream. The most persistent logjams also form in secondary channels in the multithread section and logjams in the multithread reach tend to have larger backwater storage than logjams in the single‐thread reaches. The results presented here are unique in detailing changes in logjams during the decade following abrupt recruitment of a substantial volume of large wood to a mountain stream.