Browsing by Author "Stevens-Rumann, Camille, advisor"
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Item Open Access Assessing post-fire tree regeneration and forest conversion across an elevational gradient in southern Colorado(Colorado State University. Libraries, 2023) Hastings, Amanda K., author; Stevens-Rumann, Camille, advisor; Fornwalt, Paula, committee member; Rocca, Monique, committee memberIncreased wildfire activity, with anticipated novel climate scenarios, raises concerns about forest resilience—particularly in semi-arid regions of the western US. Specifically in southwestern US and Southern Rocky Mountain forests, lack of conifer seed sources and shifts in temperature or precipitation post-wildfire may limit the recruitment of dominant conifer species. Meanwhile, hotter and drier conditions may promote the proliferation of resprouting angiosperm species, resulting in vegetative type conversions. To better understand forest susceptibility to type conversion following wildfire, I assessed early vegetation assembly 3 years post-fire, in sites that burned at low and high severity and spanned a climatic gradient in the Sangre de Cristo range of southern Colorado. Research sites were located in lower montane, upper montane, and subalpine forests, with relative dominances of Pinus ponderosa- Pseudotsuga menziesii; Abies concolor- Pinus contorta- Populus tremuloides; and Abies lasiocarpa- Picea engelmannii- Pinus flexilis- Pinus aristata; respectively. I quantified post-fire tree seedling densities and other site-specific attributes to evaluate a) how do burn severity and forest type influence early post-fire tree regeneration, b) are these forest types undergoing conversions? and c) if so, what factors are driving type-conversion?In this early assessment, I found concerns of forest conversion may be warranted for lower montane forests, with greater abundances of deciduous tree-shrub species, Quercus gambelii and Robinia neomexicana, and high shrub cover. Meanwhile, upper montane forests are likely regenerating to a similar forest composition, with early Populus tremuloides dominance and Pinus contorta regeneration. For both lower and upper montane forest types, conifer regeneration was positively correlated with legacies of low-moderate severity fire, such as overstory cover and litter/woody debris. Meanwhile, subalpine tree regeneration was driven by site-climate and topographic position, regardless of fire severity. In subalpine forests, this study suggests early post-fire conifer regeneration may be dominated by xeric and drought-tolerant species, Pinus flexilis, Pinus aristata, and Pinus contorta, where decades may pass before the establishment of shade-tolerant species characteristic of this forest type. Across all forest types, greater time is required in the post-fire period to predict ultimate recovery trajectories. However, this study serves as one of the first within southern Colorado to evaluate post-fire regeneration across a full elevational gradient and multiple forest types within a single fire footprint.Item Open Access Effects of disturbance on tree level resistance in ponderosa pine trees along the Colorado Front Range(Colorado State University. Libraries, 2024) Woodard, Kelby, author; Stevens-Rumann, Camille, advisor; Negrón, José, committee member; Rocca, Monique, committee memberForest restoration treatments are being implemented across ponderosa pine systems along the Colorado Front Range with goals of reducing risk of catastrophic wildfire, returning forest structure to historical conditions, and increasing ecosystem resilience and resistance in the face of climate change. While there are studies monitoring effects of thinning and wildfires on forest structure across the Front Range, few studies assess the effects of disturbances from wildfires and thinning treatments on tree-level resistance. Here we examined forest stand structure, growth, and defense characteristics in response to treatments and wildfires through the collection of plot level data, tree-level characteristics, and tree cores. We sampled 160 plots in areas that experienced thinning treatments between 2007-2012, were burned by low-severity wildfires (2012 Hewlett Gulch and High Park Fire, 2010 Fourmile Canyon Fire and Dome Fire, 2012 Flagstaff Fire, 2012 Waldo Canyon Fire), or that were untreated and unburned (hereafter "control"). Our findings reveal that tree growth and resin duct size significantly increased following thinning treatments. Relative resin duct area and duct density were significantly higher in trees following wildfire compared to trees that experienced thinning or to those trees within control plots. Control plots exhibited the highest mean basal area and stand density index, coupled with the lowest quadratic mean diameter, indicating high inter-tree competition, which both thinning and low-severity wildfire helped alleviate. Overall, our results highlight the beneficial impacts of both thinning and low-severity wildfire on mature ponderosa pine trees by enhancing their resistance to future disturbance, such as bark beetle outbreaks and drought.Item Open Access Fire, fungi, flora, and flow: post-fire fungal community assemblages, vegetation establishment, and soil hydrophobicity in forests of the southern Rocky Mountains(Colorado State University. Libraries, 2023) McNorvell, Michael A., author; Stevens-Rumann, Camille, advisor; Rhoades, Charles, committee member; Remke, Michael, committee member; Wilkins, Michael, committee memberWildfire is an important ecological driver of ecosystem dynamics in the southern Rocky Mountains at multiple landscape scales, guiding establishment of forest biota both aboveground and below. Size, frequency, and severity of wildfires in coniferous forests across the western United States is increasing at an unprecedented rate. Despite wildfire's significant but disparate influences on forest soils, post-fire research has often focused on aboveground vegetation in isolation from study of belowground soil characteristics and the fire ecology of soil biota. Fungi are vital to forest ecosystems for their functional roles, however, the effects of wildfire on forest-specific fungal communities and how those communities subsequently influence post-fire vegetation communities and soil environments has not been extensively researched in the region over the past several decades. This is a prominent knowledge gap, especially as fungi are highly variable across functional groups, space, and time even in unburned systems. Thus, to build on our understanding of contemporary fire ecology in forested ecosystems of the Southern Rockies, we investigate three wildfires that burned in the state of Colorado during the 2020 fire season and address three research objectives: 1) Examine the influence of forest type and fire severity on post-fire fungal community composition across soil depth and temporal gradients; 2) Determine the effects of post-fire fungal community diversity on forest understory plant diversity and abundance; and 3) Explore relationships between fungal assemblages and observed soil hydrophobicity in burned forested environments. We found that though fire severity and soil depth were the primary influences on quantified fungal diversity, the composition of fungal community assemblages was most heavily influenced by forest type: forests developed fungal communities compositionally unique to one another just two years after fire. Diversity of fungi showed significant influence on aboveground plant diversity and abundance, especially mutualistic fungi (ecto- and arbuscular mycorrhizae) and their respective plant hosts. Finally, significant relationships between fungal diversity and soil hydrophobicity were observed mediated by forest type, fire severity, soil depth, and year post-fire, though these patterns were difficult to surmise and the influence of other important variables may be at play. By more fully understanding how soil fungi interact with aboveground vegetation establishment and belowground soil conditions after wildfire, this research may help inform managers of pathways to better achieve desired post-fire outcomes by leveraging fungal relationships in soil remediation, site preparation, and conservation of post-fire forest ecosystems.Item Open Access Forest type and burn severity affect understory response to historic wildfires(Colorado State University. Libraries, 2023) Weimer, Kate, author; Stevens-Rumann, Camille, advisor; Rocca, Monique, committee member; Ocheltree, Troy, committee memberThe fire season of 2020 was unprecedented in the Western US. In one summer, three different fires individually broke the record of Colorado's largest wildfire. Understanding the recovery following these unprecedented events can lend insight into the compounding effects of wildfire and climate change. Reorganization of the understory community after disturbance can indicate changes in conditions not yet reflected in tree communities. Understory dynamics also affect watershed characteristics and wildlife, so knowledge about the influence of wildfire on understory plants is crucial. The purpose of this study is to determine if a trend toward thermophilization is being shown in understory vegetation following 4 different wildfires in 2020 and to compare the relative importance of burn severity, forest type, and other environmental factors on understory community composition. We found a trajectory toward thermophilization in high elevation forests that burned with high severity. We also that drivers of community composition varied by forest type. These findings help assess how wildfire is affecting plant communities in the 21st Century and highlight where future management concerns may be.Item Open Access Post-fire vegetation and bird habitat use in piñon-juniper woodlands(Colorado State University. Libraries, 2022) Woolet, Jamie, author; Stevens-Rumann, Camille, advisor; Coop, Jonathan, committee member; Pejchar, Liba, committee memberGlobal climate change has caused fire activity and behavior to shift from historical norms due to hotter and drier conditions. Although the ecological effects of changing fire regimes have been explored in many systems, the resilience of some forest types, such as piñon-juniper, are often overlooked. Piñon-juniper is a dominant forest type in the western US and provides breeding habitat for many obligate or semi-obligate bird species. Similarly, this system is supported by a critical mutualism, where the regeneration and infilling of these trees is reliant on several bird species that disperse piñon pine and juniper seeds. This study aimed to assess woodland resilience by evaluating post-fire forest structure and the associated avian communities one-year and 20+ years post-fire. More specifically, seedling regeneration and the habitat use of piñon-juniper obligate bird species, semi-obligates, piñon seed dispersers, and juniper seed dispersers were compared across burned, refugia, and unburned patches. Replicate patches of each habitat type were selected within three fire locations, and 3-4 bird point count stations and 1 forest inventory plot were established in each patch. No tree regeneration was observed 1-year post-fire, and after 25 years, there were few juniper seedlings and no piñon seedlings observed in burned plots. Seedling regeneration and forest structure in refugia and unburned plots were not different, regardless of fire age. Results from occupancy models indicated that Woodhouse's Scrub-jay, a piñon seed disperser, used all habitats equally. American Robin had the highest habitat use in the recent burned patches. Obligate and semi-obligate bird species had differing responses to habitat types, with the habitat use of Ash-throated Flycatcher and Spotted Towhee not differing across habitat types, Virginia's Warbler having the highest habitat use in old burn and refugia patches, the Gray Vireo, Black-throated Gray Warbler, and Gray Flycatcher having highest habitat use in unburned, refugia, and recent burn patches, and the Blue-grey Gnatcatcher having the highest habitat use in the old burn. While there is a need for longer term studies, our work highlights that even 25 years post-fire, little tree recovery is observed and the associated bird species continue to differ, emphasizing the potential transition or long recovery time in these sensitive areas.Item Open Access The ecological effects of multiple disturbances on subalpine forest structure and recovery in a changing climate(Colorado State University. Libraries, 2020) Schapira, Zoe, author; Stevens-Rumann, Camille, advisor; Hoffman, Chad, committee member; Rocca, Monique, committee memberDue to the shifting global climate, the severity, size, and frequency of climate-driven disturbances are increasing, inevitably causing disturbances to interact in time and space. Bark beetle epidemics and wildfires have historically shaped the disturbance regimes of western North American forests. Their interactive effects on stand dynamics and recovery are inadequately studied in Engelmann spruce (Picea engelmannii)- subalpine fir (Abies lasiocarpa) dominant forests; understanding these interactions is imperative to the management and health of forested ecosystems. Tree seedling densities and species composition, surface fuel loading, and stand structure characteristics were compared across 80 sites that experienced either high tree mortality from epidemic spruce beetle outbreaks (>50% affected basal area), high-severity wildfire (>90% tree mortality), post-outbreak high-severity wildfire (1-3 years post-outbreak), or no disturbance (control) in northern Colorado and southern Wyoming. The beetle-affected sites span multiple years post-outbreak from 1996-2017, ultimately comprising a chronosequence of beetle-affected stands. Structural changes in subalpine stands following spruce beetle outbreaks include species compositional shifts in overstory trees, and significant increases in fuel loading over time-since-outbreak. Tree seedling densities among outbreak and control sites differ significantly from burned areas, indicating that wildfires override the effects of repeated disturbances on regeneration. While a cursory assessment of post-outbreak regeneration based on height resulted in the appearance of consistent and stable forest recovery, subsequent aging techniques shed additional light on the drivers of subalpine tree establishment. Subalpine tree regeneration may remain suppressed in the understory for over a century; post-outbreak recovery dynamics cannot be fully understood through the use of height as a proxy for seedling age. Given the strong correlation between Engelmann spruce and subalpine fir establishment with cool and moist growing conditions, there remains significant uncertainty about post-disturbance recovery and the persistence of spruce-fir forests in a warming and drying world. It is critical to understand post-disturbance fuel dynamics and stand recovery to identify hazards for subsequent fire suppression, implement treatments to enhance forest resilience, and to understand the potential consequences of climate-induced shifts in disturbance regimes on forest health.Item Open Access The effects of post-fire logging on microclimate and surface fuels(Colorado State University. Libraries, 2021) Wooten, Jesse, author; Stevens-Rumann, Camille, advisor; Redmond, Miranda, committee member; Rocca, Monique, committee memberWildfire is increasing in size and severity in forests of the western US, driven by climate change and land management practices during the 20th century. Altered fire regimes have resulted in a greater need for knowledge on best practices for managing burned landscapes, especially in instances where a return to a previous forested ecosystem is desired. Our study location was the Spring Creek Fire in the Rockies of Colorado, where we examined soil moisture, soil temperature, and soil disturbance as well as surface fuel loading and understory vegetation recovery in areas that burned at low and high severity, a subset of which received post-fire logging treatments. Two years post-fire, we found no difference in understory vegetation response; however, logged sites demonstrated lower daily average and minimum soil moisture and higher fuel loading across most fuel size classes, and were more likely to show evidence of compaction, erosion, and rutting. This suggests that post-fire logging may create unfavorable conditions for tree regeneration while increase short term site susceptibility to reburns. Careful consideration should be taken when conducting post-fire logging to prevent detrimental ecological effects.Item Open Access The impact of wildfire on avian communities: exploring habitat associations two decades after fire(Colorado State University. Libraries, 2023) Vicini, Maria, author; Stevens-Rumann, Camille, advisor; Vogeler, Jody, committee member; Fornwalt, Paula, committee memberLarge high-severity wildfires have been affecting ponderosa pine dominated systems for decades, yet minimal long-term research has been conducted to address how avian species are responding to vegetation recovery and wildfire-driven conversion multiple decades after wildfire in ponderosa pine ecosystems of the southwestern United States. Understanding how community dynamics differ between low- and high-severity portions of burned footprints, and how vegetation structure relates to species presence is crucial for species conservation efforts, especially as wildfires in the western U.S. continue to have larger proportions of high-severity fire compared to historical fires. To address this in the Southwest, our study sought to quantify vegetation recovery, avian community dynamics across low- and high-severity sites, and quantify species-specific relationships with current vegetation structure in two post-fire footprints two decades after fire. This study focused on the Ponil Complex Fire in northern New Mexico and the Hayman Fire in southern Colorado, both of which burned in 2002. We found continued divergence between vegetation recovery at low- and high-severity sites, though this divergence was more pronounced at the Hayman Fire. We found also significant dissimilarities in avian community composition between low- and high-severity sites, and significantly lower species richness at high-severity sites across both wildfires. Forest-associated bird species presence was associated with more canopy cover and lower severity. Alternatively, lower canopy cover and higher severity were associated with the presence of a variety of grassland-, shrubland-, and desert-associated species. Our findings point to the importance of preserving pyrodiversity on the landscape to maximize suitable habitat for the greatest number of species, especially as it pertains to preserving adequate proportions of low-severity patches for forest-associated species who require intact canopy cover. However, large high-severity patches as the dominant component of the landscape will not support the most diverse array of bird communities 20+ years post fire.