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Browsing by Author "Stevens-Rumann, Camille, committee member"

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    Community risk due to wildland urban interface fires: a top-down perspective
    (Colorado State University. Libraries, 2021) Chulahwat, Akshat, author; Mahmoud, Hussam, advisor; Ellingwood, Bruce, committee member; van de Lindt, John, committee member; Stevens-Rumann, Camille, committee member
    Recent wildfire events, in the United States and around the world, have resulted in thousands of homes destroyed and many lives lost, leaving communities and policy makers, with the question as to how to manage wildfire risk. Wildland urban interface fires have demonstrated the unrelenting destructive nature of these events and signify the need to address the problem. This is particularly important given the prevalent trend of increased fire frequency and intensity. Current approaches to managing wildfires focus on fire suppression and managing fuel build-up in wildlands. Frequent suppression of small scale fires has led to the absence of a natural reduction mechanism, which in turn, results in low frequency high intensity fires. This phenomena has been termed as the Wildfire paradox and it reinforces the ideology that wildfires are inevitable and are actually beneficial; therefore focus should to be shifted towards minimizing potential losses to communities. However, reliance on these strategies alone has clearly proven inadequate. This requires the development of vulnerability-based frameworks that can be used to provide holistic understanding of risk. Mitigation strategies geared towards complete containment of wildfires within the wildlands are unrealistic. Therefore, the primary goal has to be on making communities resilient, with the purpose of minimizing potential losses. There is a paucity of information regarding the interplay between communities and wildfires. Unlike other hazards, for which there exists significant knowledge base, quantification of WUI fires is still an unanswered question for us. To better understand what factors govern the impact of WUI fires, tools to assess and quantify the risk of wildfires to communities are required. In this study, a probabilistic approach for quantifying community vulnerability to wildfires by applying concepts of graph theory is devised. A directed graph is developed to model wildfire inside a community by incorporating different fire propagation modes. Four modes are considered in this study - Convection, Radiation and Embers, and individual ignition models for each are formulated. Through these modes the graph model accounts for relevant community-specific characteristics including wind conditions, community layout, individual structural features, and the surrounding wildland vegetation. The graph model is then used to evaluate vulnerability of each component of the community using shortest path algorithms. The framework is utilized to study the infamous 1991 Oakland fire in an attempt to unravel the complexity of community fires. Centrality measures from graph theory are used to identify critical behavior patterns and evaluate the effect of fire mitigation strategies. Using the vulnerability framework developed, the risk of communities is further quantified. Risk is generally defined by three components - (1) Hazard intensity (2) Degree of exposure and (3) Exposed elements. In context of wildfires, the risk is formulated by combining the following three components - probability of wildland ignition, probability of fire reaching the community and vulnerability of community. Four different communities across the United States are selected and risk analysis is conducted for the months May-September to understand the correlation between community risk and community characteristics. Unlike current practice, the results are shown to be community-specific with substantial dependency of risk on meteorological conditions, environmental factors, and community characteristics and layout. For the final part of this study, an intervention optimization is formulated and applied to the four communities to observe the effect of different intervention measures on community risk. The findings show the need for exploring unique viable solutions to reduce risk for communities independently, as opposed to embracing a generalized approach, which is currently the case.
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    Disturbance promotes native bee biodiversity in a southwestern ponderosa pine forest
    (Colorado State University. Libraries, 2021) Gelles, Ryleigh Victoria, author; Davis, Seth, advisor; Stevens-Rumann, Camille, committee member; Ode, Paul, committee member
    Native bees are critical components of ecosystems where they provide an estimated 85% of pollination services. In recent decades, reports of global decline in bee populations have drawn concern from conservationists, compelling the need for further research on the drivers and mechanisms influencing the diminishment of native bee populations. In ponderosa pine ecosystems, land management tactics of the late 19th and early 20th century, particularly fire suppression policies, promoted dense stand structures with closed canopies, a suppressed understory, and increased surface fuel loadings. Forest restoration practices including thinning of stands and re-introduction of fire are utilized as a technique to restore historical ecosystem structures, and restoration goals in southwestern ponderosa pine forests may align with conservationists' goals of creating desirable habitat for bees by promoting resource patch connectivity, growth of understory floral species, and landscape heterogeneity. However, despite the widespread implementation of ecological restoration tactics in western forests, the effects of restoration and disturbance in general on native bee communities are not understood but could have important consequences for ecosystem function. To address this knowledge gap, the objectives of this thesis are: (1) describe the response of native bee communities to ecological disturbance, including wildfire, managed fire, and forest density reduction treatments, (2) identify structural components of ponderosa pine forests associated with site occupancy by native bees, and (3) inventory and describe the native bee fauna present in a common forest type of the Colorado Front Range. In two separate studies, native bee communities were sampled within lower-montane ponderosa pine forest systems along the Colorado Front Range over a 2-year period. Sites were representative of various wildfire severities (high and low) and forest management treatments (prescribed fire and mechanical thinning). I quantified bee α- and β-diversity and compared diversity metrics to variation in forest structure, foraging resources (floral abundance and richness), and nesting habitat (woody material). In total, 2,177 bee specimens were collected. Overall γ-diversity consisted of 5 families (Andrenidae, Apidae, Colletidae, Halictidae, and Megachilidae), 25 genera, and at least 57 species. Four main findings emerged: (1) bee species richness and diversity varied across disturbance types and were highest within 1-year post-fire and high-severity wildfire stands, (2) unique bee community compositions were associated with different disturbance types but also varied across the growing season, (3) treatment type (non-treated, thinned, or burned) was associated with differences in bee functional variation, especially nesting behavior, and (4) floral resource abundances and richness were associated with increased bee abundance, richness, and α-diversity, though stand basal area was negatively correlated with bee abundance and species richness. These collective findings have implications for forest management and indicate structural elements of ecosystems that can be managed for enhancing bee biodiversity. The data presented in this thesis provide evidence that fire-disturbed forest stands generally promote bee site occupancy compared to non-burned control stands, but this effect is likely to peak shortly after fires and then decline. In addition, distinct bee assemblages were found in stands that experienced different disturbances (e.g., thinned vs. burned vs. non-disturbed), indicating that a mosaic of disturbance histories is likely to support the greatest bee biodiversity at a landscape-scale. Further, findings here elucidate habitat structural components, specifically stand basal area and floral resource richness, that can be targeted by land managers to facilitate site occupancy by bees. Accordingly, I conclude that forest restoration practices including thinning and prescribed fire use, as well as natural fire disturbances, likely promote pollinator abundance and diversity (and ostensibly pollination services) in semi-arid ponderosa pine forests of the southwestern United States.
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    Measuring social-ecological resilience in fire prone systems of northern Colorado
    (Colorado State University. Libraries, 2023) Cheney, Alyson, author; Jones, Kelly, advisor; Salerno, Jon, committee member; Stevens-Rumann, Camille, committee member
    This thesis fills a gap in temporally and spatially applied knowledge on the perceptions people hold about social-ecological system (SES) resilience. Using a SES framework, we developed a contextualized set of resilience indicators and through stakeholder interviews and surveys we used these indicators to characterize subjective measures of SES resilience in two fire-prone watersheds of northern Colorado. Through stakeholder perceptions, we assessed current and wildfire-driven changes to resilience as well as recommended pre- and post-wildfire management actions and priorities for future systems resilience. Except for watershed processes variability, large scale wildfires did not significantly influence perceived resilience of most ecological indicators. Wildfire events, however, had strong negative influence on perceived resilience of ecosystem service indicators but were perceived to catalyze benefits in social dimensions of resilience. In terms of management actions and future resilience, stakeholders underscored a need for increased pace, scale, and connectivity of fuel treatments with particular interest in prescribed fire. While current stakeholder connectivity was high, continued prioritization of partnerships remains a focus for future resilience. Our findings can be used to improve wildfire management actions for both ecosystems and communities and our resilience indicators can be applied to comparable watershed systems to measure subjective perceptions of SES resilience.
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    Wildfire impacts on western United States snowpack
    (Colorado State University. Libraries, 2022) Giovando, Jeremy, author; Niemann, Jeffrey, advisor; Arabi, Mazdak, committee member; Fassnacht, Steven, committee member; Stevens-Rumann, Camille, committee member
    Snowpack in the western U.S. is critical for water supply and is threatened by wildfires, which are becoming larger and more common. Numerous studies have examined impacts of wildfire on snow water equivalent (SWE), but many of these studies are limited in the number of observation locations, and they have sometimes produced conflicting results. The objective of this study is to distinguish the net effects of wildfires on snowpack from those of climate. Data from 45 burned sites from the SNOTEL network are used to perform an empirical analysis to determine SWE impacts from wildfire. For each burned site, unburned control sites are identified from the same level III ecoregion. Impacts of climate changes on snowpack are analyzed first by comparing pre-wildfire and post-wildfire snow water equivalent at the unburned sites. Combined climate and wildfire effects are considered by comparing pre-wildfire and post-wildfire SWE at the burned sites. Wildfire impacts are then isolated by taking the difference between the burned and unburned sites. Four separate snow measures are considered in this analysis and include annual maximum SWE, normalized annual maximum SWE, peak SWE date, and melt-out date. Wildfires have on average advanced melt-out (9 days) and maximum SWE dates (6 days) and reduced annual maximum SWE (10%) across all the sites considered in the analysis. The combined effects of climate and wildfire have advanced melt-out and maximum SWE dates approximately 14 days and 10 days, respectively, while decreasing maximum SWE for the combined effects was approximately 10%. The wildfire-induced changes in SWE were compared to several possible controlling variables including burn severity, leaf-area index change, dominant pre-wildfire tree genus, years since the fire, and site elevation. Due to increasing wildfire magnitude, the potential vulnerability of snowpack is an important consideration for water managers. An analysis to quantify the spatial variability of wildfire impacts on snowpack within the western U.S. ecoregions and vulnerabilities of annual maximum SWE was performed. Random forest models were developed for each measure using topographic, climatic, and land cover predictor variables along with snowpack data from wildfire impacted SNOTEL sites. The results indicate terrain slope is an important variable for maximum SWE, while incoming shortwave radiation and aridity are important for peak SWE date and melt-out date changes, respectively. The largest spatial variability amongst all snow measures is maximum SWE with a range of 5% increase to over 10% decrease due to wildfire impacts. Spatial variability for peak SWE and melt-out dates varied between ecoregions with the largest range in the northern and mid-latitude ecoregions. Peak SWE and melt-out dates are expected to be earlier with the exception of the Arizona-New Mexico Mountains where later melt-out dates are possible. South-facing gentle slopes were identified as the most vulnerable for maximum SWE changes. The total snow water volume difference due to wildfires occurring between 2015 through 2020 ranged from a 1% increase in the North Cascades to a 6% reduction in the Arizona-New Mexico Mountains. A consequence of increased wildfire activity in the western U.S. has resulted in increasing post-wildfire risk assessments by federal, state, and local governments. Locations of these assessments include watersheds which have snowmelt as part of the hydrologic regime. The current gap in generalized recommendations for water managers related to parameter adjustments in snow models presents challenges for water managers performing these risk assessments. Data from wildfire impacted SNOTEL sites were again used to estimate changes in two key parameters (the melt-rate function and the snowfall threshold temperature). The observed changes from pre- and post-wildfire periods at each SNOTEL site were used to develop a suite of general linear models to adjust the melt-rate function and threshold temperature. The model inputs include readily available topographic, climatic, and land cover information. The results indicate melt-rates typically increase after a wildfire, especially for periods later in ablation season. The snowfall threshold temperatures were more variable and site dependent, although the statistically significant changes suggest increases in the threshold temperature will occur post-wildfire. The coefficients from the models suggest that changes to the vegetation canopy are most important for estimating melt-rate and threshold temperature differences beginning immediately after the fire event though approximately 10 years post-wildfire. After vegetation canopy, other important input variables include the air temperature and topographic characteristics (i.e., elevation, northness, and eastness).
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    Wildfires and precipitation in the lowlands of Guatemala: an analysis of precipitation and vegetation indices as potential wildfire drivers
    (Colorado State University. Libraries, 2023) Malaker, Tanmoy, author; Leisz, Stephen J., advisor; Pons, Diego, committee member; Stevens-Rumann, Camille, committee member
    Wildfire is an inevitable natural disaster that is considered exclusive to dry and temperate regions. However, the increasing wildfire occurrences in tropical and humid forest regions urge us to investigate the drivers of this natural phenomenon for a humid forest region. Although wildfire is inevitable, it can be managed with proper strategies; thus, identifying the drivers of wildfire in humid and tropical regions is imperative. This thesis focuses on identifying the role of precipitation as a driver for wildfire occurrences and fuel generation for fires in a humid forest ecological system in the lowlands of Guatemala (Petén). Using the data library and cloud computation system of the International Research Institute for Climate and Society (IRI), INAB (Instituto Nacional de Bosques/Guatemala's Forest Authority) fire records for Guatemala, and geospatial tools like GIS and Google Earth Engine, the thesis identifies the influence of precipitation on vegetation and wildfires in Petén. The findings suggest that precipitation's influence on Petén's wildfires is two-dimensional. Precipitation influences vegetation or total fuel generation and fire occurrences by influencing fuel availability by influencing green-up and the dry down of fuels in a humid forest ecosystem. This two-dimensional influence makes precipitation one of the most critical drivers of wildfire for tropical-humid forest ecology. Besides the seasonal accumulative precipitation, the precipitation pattern and amount at different times within a preceding season of the fire months highly influence vegetation conditions and fire frequencies. The findings also suggest that seasonal precipitation forecasting could potentially be a tool for wildfire management and forecasting.