Western Academic Research
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Divergence between historical and contemporary fire regimes at tree-ring fire history sites in dry conifer forests of the southwestern United States
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Changing fire regimes raise concerns about increasing vulnerability of dry conifer forests in the southwestern United States. However, the extent to which contemporary fire regimes may have diverged from historical patterns and processes remains the subject of considerable uncertainty, and consequently, active scientific debate. At issue is the historical role and extent of high severity fire. Here, we contrast the frequency and severity of historical (1700-1880) and contemporary (1985-2020) fires across a network of 408 tree-ring fire-scar sites in Arizona and New Mexico. We combine dendroecological records, satellite-derived metrics of burn severity, and field measures of tree mortality. Historically, low- to moderate-severity fires burned at these sites with a mean fire return interval (MFI) of 16.9 (± 10.7) years. These fire regimes ended by 1880 at most sites, initiating a long fire-free period. Over the satellite record (1985-2020) nearly half of the sites did not experience fire, underscoring a still-growing fire deficit in large portions of these landscapes. Of the sites analyzed, 26.7% burned once while 24.3% burned two or more times. In first-entry contemporary fires, 42.4% of sites burned at severity more likely than not to kill trees (CBI>1.61), anomalous for sites where trees historically survived fire for centuries. Contemporary burn severity was linked to climatic variables including maximum temperature and vapor pressure deficit, but not to historical MFI or the length of time between historical and contemporary fire events. We did not directly evaluate pre-fire fuel conditions as a driver of burn severity, but suspect variability therein was overcome by long fire-free intervals across the region. These results underscore the consequences of climate change on the severity of forest fires, but also suggest that management interventions can achieve promising outcomes given the right climatic opportunities.
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Effects of outdoor recreation on ungulate behavior in the Gunnison Basin, Colorado
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Maintaining opportunities for outdoor recreation while balancing sustainable use of natural resources presents a challenge for natural resources managers in the face of rapidly increasing recreational use. Outdoor recreation provides health and well-being benefits to humans and is often perceived as having neutral ecological impacts on wildlife and the environment. Human recreation, however, disrupts many aspects of wildlife ecology by triggering trade-offs between avoidance of perceived risk and spending time in other fitness-enhancing activities such as foraging. In the presence of human recreation, ungulates could spend more time in vigilant behavior, which could lead to lowered fitness in the long term. We deployed wildlife cameras to explore how recreation volume, the type of recreation, and the distance from trails influenced the probability of vigilance in ungulates. Mule deer (Odocoileus hemionus) and Rocky Mountain elk (Cervus canadensis) vigilance was highly dependent on recreation volume, distance to the trail, and environmental variables. Ungulate species increased vigilance as recreational volume increased. Environmental factors potentially alleviated recreation impacts in certain circumstances however the level of recreation use facilitated higher levels of vigilance in ungulates. The use of wildlife cameras to collect human recreation and wildlife behavior data should be further explored for use in wildlife studies. Additional study in compounding direct and indirect factors of recreation is needed to more fully understand recreational influences on ungulate vigilance.
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Effects of road presence and habitat covariates on sagebrush obligate bird densities
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Within the sagebrush steppe ecosystem in the intermountain west, sagebrush obligate birds occupy a variety of specialized niches. The purpose of our research was to identify the effect of road presence and habitat covariates on the density of sagebrush obligate birds during their breeding season. Roads through sagebrush threaten local bird abundance through anthropogenic disturbance and habitat fragmentation (Knick et al. 2012). However, research in the sagebrush steppe has historically focused on Sage-grouse; in our study area specifically, Gunnison Sage-grouse (Centrocerus minimus) (Young et al. 2020). Sagebrush obligate and near-obligate songbirds include the Brewer’s sparrow (Spizella breweri), sage thrasher (Oreoscoptes montanus), green-tailed towhee (Pipilo chlorusus), and vesper sparrow (Pooecetes gramineus). We assessed avian density in response to road presence and four habitat covariates at an approximate individual bird territory scale (3.14 ha or the area of a 100 m buffer around a survey point). We found that the effect of road presence varied between our study species but overall it was not a significant relationship. Additionally, we found that increased vegetation heights over 2 m were consistently associated with declines in our study species’ densities and that increased shrub cover consistently increases study species densities. These findings indicate the importance of species specific monitoring in relation to habitat fragmentation and territory patch scale habitat conditions in sagebrush steppe ecosystems.
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Evaluating differences in bee visitation in small, urban gardens and nearby areas in West Virginia
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Bee species richness has declined globally in recent decades due to several intertwined factors. Urbanization has both positive and negative effects on bees, with species responses being highly trait- and scale-specific. Urban environments differ from natural environments in the types of habitat and food resources they provide, but they still have the potential to provide valuable habitat to increase bee abundance and diversity. Although research on bee diversity has been conducted in cities, there has been little conducted in small towns, despite their habitat and conservation potential due to their proximity to natural areas and lack of highly developed impervious surface areas. The objective of this study was to evaluate differences in bee floral visitation in backyard gardens and nearby natural areas. In a small town, I surveyed eight sites weekly using a variable transect walk method to capture and identify bees and the flowers they landed on. There were significantly more bees and flowers at the garden sites, and floral abundance was the strongest indicator of bee visitation. The gardens also had slightly later peaks in bee visitation than the natural areas, and there were differences in floral visitation preferences for bees at the two site types. This work will help inform research and conservation practices about the potential of small towns as bee conservation areas.
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Extent of recent fire-induced losses of ponderosa pine forests of the southwestern US
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Fire has shaped western ponderosa pine (Pinus ponderosa) forest landscapes for millennia. Yet, contemporary land management coupled with warming and drought has led to shifts in forest structure and severe wildfires. A growing body of evidence suggests that under altered fire regimes and climate change, ponderosa pine forests may be vulnerable to fire-driven conversion to a different forest type or non-forest vegetation. However, the extent and direction of recent fire-induced changes in southwestern US ponderosa pine forests have not been subject to region-wide evaluation. Here, our objective was to assess recent fire effects in ponderosa pine forests using long-term repeated samples of stand composition and structure from the US Forest Service’s Forest Inventory and Analysis (FIA) program and satellite-derived burn severity (predicted Composite Burn Index; CBI and difference normalized burn ratio; dNBR). We compiled and analyzed FIA plots dominated by ponderosa pine and associated species within the southwestern states of Arizona and New Mexico to quantify regional trends for ponderosa pine (e.g., forest losses or gains), link changes to wildfire severity, and characterize vegetation changes. Among our 685 plots, we found 26% of plots burned at least once from 1996-2017. Plots that burned within the study period exhibited a 46% loss of ponderosa pine trees and plots that did not burn decreased by 11%. Small ponderosa pine trees (12.7-24.5 cm diameter) exhibited the greatest declines in the number of trees and basal area compared to trees greater than 24.5 cm. Overall regeneration rates decreased over time, and approximately 11% of plots lost all ponderosa pine. Satellite-derived burn severity (predicted CBI) was a strong predictor of tree mortality and more than half of burned plots burned at moderate-high severity levels. Post-fire vegetation was influenced by fire severity and we observed transitions in species composition, with resprouting species (Quercus gambelii) establishing post-fire more than any other new species. This study contributes to an emerging ecological understanding of forest vulnerability to changing disturbance regimes. Methods employed herein offer scalable opportunities to quantify changes across forest biomes using long-term monitoring data. As importantly, our findings inform regional and local land management efforts to sustain these valued forest types in an era of change. Our results point toward two key themes for land management: restoring low-severity fire regimes and retaining large trees to ensure the long-term persistence of ponderosa pine forests in the southwest US.
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Reducing human-bear conflicts : researching and analyzing factors influencing conflicts in the Gunnison Valley
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Human-wildlife conflicts are increasing as population growth, habitat conversion, and climate change accelerate challenges for species that interface with urban and rural communities. In the Gunnison Valley, like many areas throughout the west, such conflicts are increasing between black bears and city residents. Black bears are adaptable mammals and exhibit different behaviors in response to selective pressures (e.g., temperature and precipitation changes, food availability, access to water, etc.). For example, warmer temperatures in early spring cause black bears to emerge from hibernation sooner when their traditional sources of food may be scarce. To help the City of Gunnison coexist with black bears, I did three things for my master’s project: 1) I gathered existing Colorado Parks and Wildlife (CPW) black bear conflict data looking for conflicts within the City of Gunnison and gathered regional harvest data and compiled, mapped, and analyzed these data to determine conflict hotspots and possible correlation of conflict with temperature and precipitation, and human use of the landscape; 2) I reviewed existing climate models for the Gunnison region and identified predicted changes of abiotic and biotic factors associated with black bear foraging needs and hibernation behaviors; 3) Using the information that I gathered and analyzed, I consulted with individuals from the City of Gunnison, the citizens of the region, and CPW to create a human-black bear conflict management plan designed to reduce local human-black bear conflict with varying levels of implementation strategies.
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Ruckus on the river: how river recreation affects breeding great blue herons in a mountain valley in Colorado
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Anthropogenic impacts to wildlife populations represent a reoccurring theme in wildlife management as the human population expands into wild landscapes. Our study focused on a great blue heron (Ardea herodias) colony of approximately 20 nests uniquely located along the Slate River near Crested Butte, Colorado. This high mountain stream increasingly draws river recreationists, especially stand-up paddle boarders. Our study assessed how human activities around the Slate River influenced heron behavior. We quantified human activities through one hour observations and heron responses through behavioral sampling. High hourly rates of human activities near the heronry coincided with brood rearing and fledging. Road traffic dominated all the types of human activity during all times of day and heron seasons; however, it only accounted for 0.004% of heron disturbances. In contrast, river recreation comprised less than 1% of all the activities in the valley, but accounted for 80-100% of heron disturbances. Our research showed that watercrafts floating directly under nesting great blue herons caused hunkering, alert, and flushing behaviors in over 80% of the herons at the colony. Of the 58 observed river recreation events, individual herons exhibited disturbance behaviors 388 times, and 57 herons flushed from the nest or surrounding wetland. During floating events, herons significantly decreased time spent in self-maintenance behaviors, their predominant undisturbed behavior. Foraging, nest maintenance, brooding, and agonistic behaviors ceased altogether during river recreation events. Floating event characteristics influenced the intensity of the heron response. Events that elicited more disturbance included larger groups (greater than three watercrafts), clustered groups floating through the colony with little separation between
watercrafts, groups with floaters standing upright on their boards, groups that produced noise, and groups that stopped underneath the colony. Our study demonstrates that river recreation can negatively impact great blue heron breeding and that spatial segregation between the birds and recreationists is required during the nesting season for effective species conservation.
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The Influence of Compost on Rangeland Soil Microbial Community Composition and Soil Organic Carbon Sequestration
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Atmospheric concentrations of CO2 have reached unprecedented levels, posing a threat to the health of the biosphere. Soils store the largest amount of terrestrial carbon (C) and can be used as a method for sequestering atmospheric C. The cycling of C between the atmosphere and terrestrial ecosystems is directly influenced by soil microbial activity and respiration. Compost amendments to soil systems have the potential to shift the composition of the microbial community and to increase C sequestration potential. Rangeland ecosystems represent a valuable opportunity for implementing climate mitigation practices with compost amendments. This study aims to answer the following questions: (1) Does a one-time compost addition to rangeland soils induce a shift in the microbial community one year post application? (2) Does compost addition increase or decrease the rate of CO2 efflux over the growing season? and (3) Does MRT of SOC differ between soils treated with compost and soils not treated with compost?
Three rangeland sites located in Gunnison, Colorado were manipulated with compost additions in June of 2019: Coldharbour (CH), Parker Pastures (PP) and Wiley Lane (WL). Soil moisture, temperature and respiration rates were measured throughout the 2020 growing season. Soil samples were collected and analyzed for bulk density, SOC pool, nitrogen (N) pool and microbial phospholipid fatty acids. A one-time compost application had no effect on the microbial community composition of rangeland soils one year post application. Daily CO2 efflux rates were not influenced by compost application, however, the cumulative release of C-CO2 2 over the growing season was higher in the non-composted soils. The largest difference of cumulative efflux between treatments was seen at the CH site where control soils had an average C-CO2 efflux of 811.1 g C m2-1d-1 and treatment soils had an average C-CO2 efflux of 652.8 g C m2-1d-1. Mean Residence Time (MRT) of SOC across sites ranged from 0.64 – 3.21 years and was significantly higher in the treatment soils than in the control soils. On average, compost application treatment increased MRT of SOC by 0.35 years across sites. As the C pools were not significantly different between treatments, the significantly lower efflux observed in the treatment soils was responsible for the increase in MRT of SOC found. These findings present a valuable representation of how improved land management practices on rangeland soils can positively contribute to soil C sequestration.
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The reproductive ecology of Astragalus microcymbus
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Astragalus microcymbus Barneby (Fabaceae) is a rare endemic to Gunnison and Saguache counties in western Colorado, ranked as critically imperiled by the Colorado Natural Heritage Program. The purpose of this study was to further investigate this plant’s reproductive ecology including reproductive success, pollination ecology and post-primary dispersal seed ecology. To investigate these components of A. microcymbus reproduction, this study was guided by the following questions: 1.) What is the reproductive success of A. microcymbus as measured by fruit to flower and seed to ovule ratios? Does reproduction vary across sites and what factors influence its reproductive success? 2.) Does A. microcymbus require pollinators for successful seed set? If so, what are its primary pollinators? 3.) Does A. microcymbus have a viable soil seed bank and how does it vary across the landscape? Can insight into the secondary dispersal mechanisms and occurrence patterns of A. microcymbus be gained by the spatial distribution of the seed bank and individuals? Our methods included flower, fruit, seed, and ovule counts, monitoring herbivory interactions, conducting pollinator exclusion experiments, pollinator visitation observations and identification, collecting soil seed bank samples, and describing microhabitat characteristics of individuals. In 2019, we found mean fruit set per plant ranging from 0.25 to 0.30, and seed set per fruit averaging 0.29. In 2020, low reproduction was observed due to the impacts of small mammal herbivory and drought, which limited the reproductive success study and the pollinator exclusion experiment. The genera Ashmeadiella (Megachilidae) and Anthidium (Megachilidae) were observed visiting and eliciting the pollination mechanism of flowers. Astragalus microcymbus exhibited a soil seed bank that decreased in density with increasing distance from parent plant. At the intermediate distance from the parent plant (0.5 m), fewer seeds were found in microsites with higher bare ground exposure, suggesting the process of overland flow or wind influence seed dispersal. Finally, established plants occurred in areas closer to vegetation and with higher vegetation cover, suggesting vegetation patches may serve as seed catches and/or nurse plants facilitating seedling establishment and survival. This information broadens our understanding of the life-history and ecology of this rare endemic and informs conservation efforts.
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