Mountain Scholar :: Browsing by Author "Rocca, Monique, committee member"

Browsing by Author "Rocca, Monique, committee member"

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Open Access
Advancing prescribed fire science through numerical simulation and improved reporting practices
(Colorado State University. Libraries, 2022) Bonner, Sophie R., author; Hoffman, Chad, advisor; Linn, Rodman, committee member; Tinkham, Wade, committee member; Rocca, Monique, committee member
Planning a prescribed burn that is safe and effective relies on land managers understanding how a complex suite of interactions between the burning environment (e.g., fuels, fire weather, and topography) and ignition factors influence fire behavior and effects. As the field of prescribed fire science has grown, more questions have arisen regarding how the spatial structure of forests and the ignition pattern affect the ecological outcomes of these burns. Advancing our understanding of these factors is crucial to provide managers with quality, evidence-based science that can inform prescribed fire planning. In this two-part thesis, my objectives were: i) to evaluate reporting quality in recent prescribed fire literature and suggest minimum reporting standards for future prescribed fire experiments, and ii) to explore the potential effects of complex forest fuel structures and ignition patterns on fire behavior and the resultant ecological effects during prescribed burns. In Chapter 1, I present results from a literature review of reporting standards from over 200 prescribed fire experiments conducted from 2016 to 2020. My results suggest substantial shortcomings in the reporting of critical data that limit the utility of prescribed fire research. Specifically, I found that specific information on burning conditions such as fuel moisture (22%), quantitative fuel loads (36%), fire weather (53%), and fire behavior (30%) were often not reported by the authors. Further, I found that only 54% of the studies provided descriptions of the ignition characteristics. Given these common deficiencies, suggested minimum reporting standards are proposed for future prescribed fire experiments which can be used to increase the quality, applicability, and reproducibility of prescribed fire science, facilitate future research syntheses, and foster actionable science. In Chapter 2, I evaluate how forest structural complexity and ignition pattern impact crown damage during simulated prescribed fires in longleaf pine (Pinus palustris) dominated forests of the southeastern United States. My results show that - regardless of forest structure – using a strip-head ignition pattern consistently produced more crown damage than spot-head or alternative spot-head ignition patterns. In terms of forest structure, I found forests with greater structural complexity resulted in more crown damage than less complex forests. More specifically, I observed forests with more aggregated horizontal spatial patterns, greater vertical complexity, and moderate to high amounts of canopy cover to produce more severe fire behavior than regularly spaced, single-story forests with sparse canopy cover. These findings suggest that managers need to consider a forest's structure and their choice of ignition pattern when planning prescribed burns to ensure they meet ecological objectives.
Open Access
Assessing forest plan revision under the 2012 planning rule: understanding policy implementation and organizational learning
(Colorado State University. Libraries, 2017) Ricco, Gwendolyn M., author; Schultz, Courtney, advisor; Rocca, Monique, committee member; Williams, Dan, committee member
In 2012, under the National Forest Management Act (NFMA), the U.S. Forest Service promulgated a new planning rule that was a significant change from past planning regulations. For example, the concepts of ecological integrity and climate change adaptation were introduced as important management priorities. This research identified lessons learned, innovations, and best practices under the 2012 planning rule and characterized how organizational learning occurred during times of policy transition and implementation. I used learning frameworks to identify types of learning occurring. In addition, early policy implementation is a critical time for an organization to experience learning, but there has been relatively little literature that looks at how learning occurs during this period. The policy implementation literature discusses both top-down and bottom-up variables impacting implementation, and I considered how these may also affect learning. We collected qualitative data from the 2016 Planners' Meeting in Fort Collins, Colorado held by the Forest Service and conducted 25 semi-structured, follow-up interviews with planning staff to understand what types of learning were occurring during early implementation of a new policy, determine how the factors that affect policy implementation affect learning, and identify how the agency could better support learning throughout the implementation of the 2012 planning rule. This study revealed that although the Forest Service is displaying some characteristics of a learning organization, such as creating social learning networks, the agency needs structural and cultural changes to reach their goals and overcome barriers. Much of the learning that is occurring happens at the individual level, and a critical challenge is how to improve diffusion and consolidation of the knowledge being gained. Therefore, the agency will need to create entirely new structures to capture their knowledge and lessons learned to better encourage continual learning. This could include improving trainings and workshops and offering mentoring opportunities but may also require reorganization and dedication of new staff positions to support more effective organizational learning.
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 member
Increased 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.
Open Access
Causes, consequences, and management of tree spatial patterns in fire-frequent forests
(Colorado State University. Libraries, 2022) Ziegler, Justin Paul, author; Hoffman, Chad, advisor; Ocheltree, Troy, committee member; Redmond, Miranda, committee member; Rocca, Monique, committee member
Increasingly, restoration treatments are being implemented to dually meet wildland fire hazard reduction alongside ecological objectives. Restoration treatments however deviate from conventional fuels treatments by emphasizing the re-creation of forest structure present prior to EuroAmerican settlement, notably the retention of single and grouped trees interspersed between canopy openings. As these historical forests persisted over cycles of fire returns, it is assumed that restoring these historical complex tree spatial patterns will, in turn, restore historical ecological processes. This includes more benign fire behavior that results in only partial tree mortality, allowing persistent and partial retention of forest cover over cycles of fire return. The qualitative description of historical forest structure, lacks, however, a clear process-based explanation detailing the interactions of heterogeneous forest structures and fire. While fires were historically frequent, it is unclear what role fire played in the genesis and maintenance of tree spatial patterns. If models of tree spatial dynamics can be improved and the interactions between tree spatial patterns and fire can be elucidated, forest managers will have an improved understanding of the implications of restoration-based fuels hazard reduction treatments both during fire-free periods and during fire events. The aims of this dissertation were to: 1) explore the causes of tree spatial patterns in dry fire-frequent forests; 2) investigate the consequences of tree spatial patterns on potential fire behavior and effects; 3) determine how alternate silvicultural strategies targeted at manipulation of tree spatial patterns can influence fire behavior and effects. In Chapter 2, I explored spatial patterns of tree regeneration over 44 years in absence of fire. In cooler periods, regeneration preferred clustering in openings, including openings following overstory mortality and away from overstory trees. Mortality risk of regeneration was heightened nearer overstory trees. In warmer periods, these trends reversed, likely because of a 'nurse effect' from the overstory. In anticipation of climate change, these results suggest silviculturists may benefit by capturing regeneration mortality in within openings while keeping regeneration near the overstory. In Chapter 3, I found that regenerating trees also form heterogeneous patterns following stand-replacing fires. In these sparse, early seral forests, all species were spatially aggregated, partly attributable to the influence of topography and beneficial interspecific attractions between ponderosa pine and other species. Results from this study suggest that scale-dependent, and often facilitatory, rather than competitive, processes act on regenerating trees. In Chapter 4, I studied the interaction between fire and tree spatial patterns, both historically and in modern forests. Tree mortality in the historical period was clustered and density-dependent because tree mortality was greater among small trees, which tended to be assembled in tightly spaced clusters. Tree mortality in the contemporary period was widespread, except for dispersed large trees, because most trees were a part of large, interconnected tree groups. Postfire tree patterns in the historical period, unlike the contemporary period, were within the historical range of variability found for the western United States. This divergence suggests that decades of forest dynamics without significant disturbances have altered the historical means of pyric pattern maintenance. In Chapter 5, I examined how fuels treatment designs with different manipulations of tree spatial patterns may influence treatment effectiveness. I simulated fires on hypothetical cuttings which manipulated the arrangement of crown fuels horizontally and vertically, either increasing the distance between tree crowns or not, and either removing small trees or not. All cutting methods reduced fire behavior and severity, but the results confirm possible tradeoffs between ecological restoration and hazard reduction; treatments that separated tree crowns reduced severity the most because these treatments reduced crown fire spread. But these can easily be overcome where restoration treatments incorporate small tree removal, because this action limits crown fire initiation. Managers could also incorporate managed fires to reduce surface fuel loads and use more aggressive cuttings to further gains in hazard reduction, regardless of cutting method used.
Open Access
Competition from neighboring trees in eucalyptus monoculture and in mixed species native forest restoration plantations
(Colorado State University. Libraries, 2012) Luu, Trung Canh, author; Binkley, Dan, advisor; Rocca, Monique, committee member; Laituri, Melinda, committee member; Kelly, Eugene F., committee member
Competition has been recognized as a crucial factor in determining stand structure and productivity. However, competition is not a simple pattern. Its intensity and importance vary with structures of neighboring tree size and composition, and nutrient gradients. Our studies examined the influence of neighborhood uniformity on growth of individual trees in Eucalyptus monoculture, and competition between pioneer and non-pioneer species in mixed native species restoration plantations by developing a number of alternative neighborhood growth models. Our analyses showed that neighborhood uniformity of tree sizes had significant effects on growth of individual clonal Eucalyptus trees and these effects increased with increasing age of stand because stand and neighborhood tree size became less uniform with age. For competition from pioneer trees to non-pioneer trees, competition from neighboring trees had strong effects on the growth of individual non-pioneer trees, and the intensity of competition from neighboring trees varied with focal tree species guild and degrees of silviculture interventions. For example, non-pioneer legumes experienced competition as a function of neighboring tree sizes and distances only. Non-pioneer non-legumes experienced competition as a function of neighboring tree sizes and distances, and also by the identity of neighboring species guilds. The non-pioneer non-legumes experienced stronger competition in the intensive silviculture treatment, probably resulting from the neighboring species guild of pioneer non-legumes, unlike the non-pioneer legumes. Although intensive silviculture initially enhanced forest stand productivity (both density and tree size), strong competition from fast-growing lowered the later growth of individual non-pioneer trees. Our analyses suggested implications to: (i) increase and maintain stand uniformity to increase stand stem productivity and quality; and (ii) control strong, even exclusive completion in some cases from pioneer trees to non-pioneer trees through matching species to be mixed and managing their abundance.
Open Access
Conifer regeneration and fuels treatment longevity in dry mixed-conifer forests of the Colorado Front Range
(Colorado State University. Libraries, 2018) Fialko, Katie, author; Ex, Seth, advisor; Fornwalt, Paula, committee member; Hoffman, Chad, committee member; Rocca, Monique, committee member
Throughout much of the western United States, wildfires have been increasing in size and severity. To prevent negative impacts to communities and ecosystems, costly fuels reduction treatments are being applied to dry, mixed-conifer forests in Colorado and throughout the southern Rockies. The objective of this project was to make inferences about treatment longevity by determining how site, treatment, and vegetation characteristics of treated areas influence the abundance and composition of conifer regeneration, which can serve as fuels to initiate a high severity wildfire. Thinning and mastication treatments ranging in age from 5-14 years old on north and south aspects were examined. Time since treatment and residual overstory density and composition, along with aspect, had the greatest influence on the abundance of Douglas-fir and ponderosa pine regeneration in fuels treatments. Conifer regeneration did not vary by mastication vs thinning treatment type. Although Douglas-fir advance regeneration abundance decreased over time since treatment, it comprised 50% of all regeneration observed. This is a concern because advance regeneration will reduce treatment longevity more than the gradual accumulation of post treatment seedlings, and because it has the potential to release. Post treatment Douglas-fir regeneration was positively related to Douglas-fir residual overstory density but had no relationship with time since treatment. Post treatment ponderosa pine regeneration, however, increased with time since treatment and was negatively related to total residual overstory density. These findings indicate that while Douglas-fir regeneration may belimited by the lack of residual Douglas-fir in the overstory to provide a seed source, treatments are effectively acting as shelterwood regeneration treatments to increase the abundance of ponderosa pine. Lastly, average abundance of all conifer regeneration was five times greater on north aspects than on south aspects. Forest managers implementing future fuels reduction treatments, or planning the re-treatment of existing units, should monitor advance regeneration for potential release, anticipate a greater post treatment regeneration response on north aspects, and possibly expect a shift in future stand composition towards ponderosa pine.
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 member
Forest 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.
Open Access
Engelmann spruce and subalpine fir stand dynamics in north central Colorado
(Colorado State University. Libraries, 2015) Derderian, Drew Phillip, author; Binkley, Daniel, advisor; Paschke, Mark, committee member; Rocca, Monique, committee member
Stemwood biomass and production were measured in a 600-year chronosequence of stands consisting of Engelmann spruce and subalpine fir in the Colorado Front Range. The stands were part of a chronosequence established and measured in 1984. The original chronosequence showed near-constant biomass of spruce after approximately 250 years of development. Spruce production also had remained nearly constant after an initial rise and fall during the first 250 years. Fir biomass decreased more than that of spruce after around 150 years. Fir biomass remained at lower consistent sub-dominate values through the end of the chronosequence. Fir's high production from early stand development decreased and remained constant after approximately 175 years of development. Changes over the most recent 29 years did not follow the patterns in the 1984 chronosequence: spruce biomass dropped by 70% with little change in fir biomass. This resulted in a 47% average decrease in total stand biomass since 1984. Stand biomass showed no relationship with stand age. Spruce beetle-kill appeared to have played a major role in live biomass decline in all stands. Net increment was negative in fir as increases in fir production were more than offset by fir mortality. The stands investigated have developed from post-fire initiation and, although there was no evidence of subsequent major disturbance in 1984, severe beetle infestation since then has altered expected trends in spruce-fir forest structure. Stand age pattern projections will likely continue to be altered by disturbances and changing disturbance regimes.
Open Access
Establishing Carex scopluorum seedlings to restore the vegetation of Tuolumne Meadows, Yosemite National Park, USA
(Colorado State University. Libraries, 2018) Booher, Melissa, author; Cooper, David, advisor; Ocheltree, Troy, committee member; Rocca, Monique, committee member
Wet meadows are critically altered and at-risk ecosystems globally and in the Sierra Nevada of California. The low vegetation cover created by legacy disturbances is a restoration priority due to the importance of organic-rich soils for future plant establishment, carbon storage, and water retention. Wet meadows are characterized by seasonally saturated fine-textured mineral soils with significantly more organic matter than surrounding areas, shallow groundwater (< 1 m), and vegetation dominated by herbaceous plant species. This research focused on the establishment requirements of seedlings of the native sedge Carex scopulorum in Tuolumne Meadows, Yosemite National Park, USA. I provide critical information on biomass contribution of a key wet meadow species that could also be used in other restoration efforts in similarly degraded subalpine meadows. We tested the suitability of this species for use in future restoration work and assessed the growth of C. scopulorum seedlings in a fully factorial experiment with small mammal herbivore exclosures and planting density treatments. Seedlings were planted in June 2016 and survival was high, approximately 98%, living through the summer of 2016 and 71% surviving through the end of the 2017 summer. After two seasons of growth, planted seedlings more than doubled in area (horizontal tiller spread) and nearly doubled their longest leaf lengths. Total C. scopulorum seedling biomass increased more than six-fold from the delivered seedlings in 2016 to end of the 2017 growing season. Carex scopulorum seedlings had greater mean biomass, 703.44 g/m2 ± 246.54, than all other species in our study plots and had more than twice the belowground biomass per unit area of other herbaceous species sampled. In addition, planted C. scopulorum seedlings allocated a greater portion of their biomass below-ground (higher mean ratio) than all herbaceous species (all comparisons p = <0.05) other than Carex subnigricans (p = 0.051). Our results indicate that C. scopulorum is an appropriate species for restoration in Tuolumne Meadows where increasing biomass inputs to the system is a priority and could be a valuable tool for revegetation and restoration of other degraded meadows in the Sierra Nevada.
Open Access
Estimating pre-fire forest structure with stereo imagery and post-fire lidar
(Colorado State University. Libraries, 2016) Filippelli, Steven, author; Lefsky, Michael, advisor; Rocca, Monique, committee member; Sibold, Jason, committee member
Lidar has become an established tool for mapping forest structure attributes including those used as inputs for fire behavior and effects modelling. However, lidar is rarely available to document pre-fire conditions due to its sparse availability. In contrast, aerial imagery is regularly collected in many regions, and advances in stereo image matching have enabled the creation of dense photogrammetric point clouds similar to those from lidar. As part of a study of the physical and ecological impacts of the 2012 High Park Fire, we generated a photogrammetric point cloud from pre-fire aerial imagery collected in 2008 and calculated forest height using a digital terrain model generated from a 2013 post-fire lidar collection. A suite of canopy height and density metrics were created from both the pre-fire photogrammetry and the post-fire lidar point clouds. These metrics were compared to each other and to forest structure attributes measured in the field. For unburned areas, we found strong relationships between corresponding lidar and photogrammetry height and density metrics with biases that were consistent with known differences in each sensor’s method of sampling the canopy. Regressions models of field-measured forest structure attributes incorporating both lidar and photo metrics demonstrated that a single equation could estimate some forest structure attributes without significant intercept or slope bias due to the source of the metrics (i.e. photo or lidar). Models of aboveground biomass on unburned plots had similar root mean square errors for lidar (29.3%), photogrammetry (31.0%), and combined data sources (RMSE = 29.1% and source intercept bias = 34.64 Mg ha-1 and slope bias = -0.28). Similar results were obtained for Lorey's height, basal area, and canopy bulk density. Models of structure in burned areas derived from post-fire lidar had lower performance than photogrammetry due to the fire's consumption of canopy materials which generally reduced the explanatory power of lidar density metrics. Pre-fire forest structure information could aid assessments of contributing factors such as canopy fuels and fire effects such as loss of biomass. The wide spatial and temporal coverage of aerial photos and growing coverage of lidar could enable many other applications of combining photogrammetry with lidar, including assessments of changes in forest carbon storage.
Open Access
Facies reconstruction and detrital zircon geochronology of the Ingleside/Casper Formation
(Colorado State University. Libraries, 2018) Nair, Kajal, author; Egenhoff, Sven, advisor; Singleton, John, advisor; Rocca, Monique, committee member
Mixed siliciclastic-carbonate deposits of the Ingleside/Casper Formation in northern Colorado and southeastern Wyoming developed along the flanks of the Ancestral Front Range during the Late Paleozoic. This study establishes a sedimentological model for the Ingleside/Casper Formation along with using detrital zircon data to identify siliciclastic sediment sources for Late Paleozoic deposits in two Ancestral Rocky Mountain basins along the Ancestral Front Range and Uncompahgre Highlands. The stratigraphic successions of the Ingleside/Casper Formation display a diverse suite of carbonate and siliciclastic lithofacies in close lateral and vertical association with each other. The six different siliciclastic facies and their subfacies identified in this study include: (1) cross-bedded sandstone (tabular cross-bedded sandstone and trough cross-bedded sandstone), (2) horizontally-bedded sandstone, (3) massive sandstone, (4) conglomeratic sandstone, (5) ripple-laminated sandstone (asymmetric current ripples, moderately-steeply climbing ripples, and gently climbing ripples), and (6) silt-rich siliciclastic mudstone. The three different carbonate facies and their subfacies identified in this study include: (1) carbonate mudstone-wackestone, (2) carbonate packstone (packstone with non-skeletal grains and packstone with bioclasts), and (3) carbonate grainstone (grainstone with non-skeletal grains and grainstone with bioclasts). Thinning and/or pinching out of carbonate facies accompanied with a gradual increase in siliciclastic sedimentation is observed laterally across the study area from north to south. Eight stratigraphic intervals are recognized from correlations across a north-south transect of 120 km and each interval displays a lithofacies assemblage dominated either by carbonates or siliciclastics. Both carbonate and siliciclastic successions display small-scale fining-upward trends, with coarsening-upwards being partially or wholly absent across the study area. One of the eight intervals (termed Interval 6) is of significant interest in this study because it displays a unique lithofacies assemblage, with it being the only interval where trough cross-beds of facies 1B occur. Overall, carbonate units vary in the extent to which they onlap onto siliciclastic strata throughout the succession: Intervals 1 to 4 record a successive advance of onlap towards the south, whereas intervals 5 to 8 record a retreat of onlap and a successive northwards migration of carbonate strata. The nine different lithofacies and their subfacies identified in this study represent an array of shallow-marine paleoenvironments that include foreshore, shoreface, offshore transition, and offshore, and terrestrial settings comprising coastal eolian dunes and fluvial systems. Stratigraphic distribution of facies suggests that deposition in a shallow-marine environment alternated between dominantly siliciclastic and dominantly carbonate, mainly as a result of fluctuations in the input of siliciclastic sediment and its effect on carbonate deposition. In a distal direction, both siliciclastic and carbonate facies graded into carbonate mudstone that is identified as the most distal setting across all stratigraphic successions studied here. The Ingleside/Casper succession is interpreted to consist of two superimposed scales of sea-level fluctuations with the small-scale cycles represented by deepening-upwards successions across the study area, and a superimposed large-scale sea level curve recorded in the varying onlap of carbonates. The superimposed curve shows an overall transgression in the lower part of the succession succeeded by a regression in the upper part. Independent of this type of sea-level curve, dry eolian dunes dominated the stratigraphic record during Interval 6 and reflect a sharp change in climate to more arid conditions that accompanied the exclusive formation of dunes during this time. The sedimentological study suggests that deposition of the Casper/Ingleside Formation was governed by the two orders of sea-level oscillations and also climate change, both operating on two separate scales. The general fall in sea level and increase in aridity in the upper Ingleside/Casper Formation is attributed to the onset of a major Gondwanan glaciation phase that culminated during the Pennsylvanian-Permian transition which is likely to be located at the very top of this unit. Based on exclusively sedimentological considerations, this study therefore suggests that the Ingleside Formation, which is typically assigned a Permian age, was most likely deposited during the Late Pennsylvanian. This interpretation is also based on the correlation of the Coloradoan Ingleside Formation to the Casper Formation in Wyoming that contains a known Late Pennsylvanian fussuline assemblage. This study also presents new detrital zircon U-Pb geochronology data from the type section of the Ingleside Formation at Owl Canyon, and the Molas and Hermosa Formations near Molas Lake to understand Late Paleozoic sediment provenance and dispersal patterns across Colorado. U-Pb ages on 120-150 zircons were determined from each sample using LA-ICPMS, and ages with excessive discordance (>20% discordant or <5% reverse discordant) were rejected. All samples contain between 5% and 10% concordant Paleozoic aged zircons ranging from 330-490 Ma. Other significant age distribution peaks identified range between 990-1200 Ma, 1340-1500 Ma, 1600-1800 Ma, and 2500-3500 Ma. The wide spread of zircon age populations record a mixed Laurentian derivation comprising local and distal sediment sources. Paleozoic-age zircons are interpreted to coincide with high magmatic flux during the Taconic and Acadian orogenies in the Appalachian orogen. The diverse components in the U-Pb age data suggest that a widespread sand-dispersal system that transported local and distant sediment sources along the Ancestral Rockies was operational during the Late Paleozoic. Areas of eolian recycling observed in the Ingleside and Molas Formations points towards eolian systems playing an important role in transportation of distally-sourced zircons during Late Paleozoic time. Additionally, the U-Pb detrital zircon data indicate that a shift from non-marine to marine deposition across the Fountain-Ingleside transition was accompanied by a decrease in locally-sourced detrital zircons, most likely marking the cessation of Ancestral Front Range uplift. Conversely, the shift from non-marine to marine deposition across the Molas-Hermosa contact was accompanied by an increase in locally-sourced detrital zircons, most likely marking the initiation of the Uncompahgre uplift.
Open Access
Forest range shifts under climate change: microenvironment impacts to tree recruitment at a climatic ecotone
(Colorado State University. Libraries, 2019) Foster, Alison Connolly, author; Redmond, Miranda, advisor; Martin, Patrick, advisor; Battaglia, Michael, committee member; Rocca, Monique, committee member
Warming across the western United States is projected to cause dramatic shifts in tree species recruitment, with the most pronounced changes in composition at range edges where species are at their thresholds of reproductive tolerance. Yet microenvironments experienced by juvenile trees can be decoupled from regional climate due to variations in canopy cover, microtopography, and organic matter. As a result, tree recruitment may be strongly controlled by microenvironments and not follow species range projections based on regional climate, even at ecotone boundaries in which species at their upper range distributions are predicted to increase in density. This is likely especially pronounced in undisturbed forests with dense canopy cover in which microclimate is more strongly de-coupled from regional climate. To address these hypotheses of tree recruitment at species range margins we conducted a field experiment and observational study at the upper montane – subalpine ecotone on the Colorado Front Range. We characterized site microenvironment and observed germination and survival of six common conifer species, Douglas-fir, ponderosa pine, lodgepole pine, subalpine fir, Engelmann spruce, and limber pine. To quantify water availability and wildlife limitations, we sowed seeds from five study species and applied treatments of simulated precipitation and wildlife exclusion. Strong recruitment limitations were observed for nearly all species in experimental and observational studies, with strong negative effects of low soil moisture and maximum temperature. Notably, only subalpine fir exhibited increased seedling dominance, likely due to the limited light availability and cooler temperatures associated with shaded microenvironments. Recruitment success was unrelated to range position and do not match established migration predictions for these species. This research further illustrates the complexity of recruitment dynamics and the need to study regeneration at multiple scales.
Open Access
Forest soil C and N responses to salvage logging and belowground C inputs in bark beetle infested stands
(Colorado State University. Libraries, 2020) Avera, Bethany N., author; Cotrufo, M. Francesca, advisor; Rhoades, Charles, committee member; Rocca, Monique, committee member; van Diepen, Linda, committee member
Managing forest ecosystems in this era of global change requires a fundamental understanding of forest soil properties and processes. Forest disturbance events are projected to increase in severity and frequency, requiring a better understanding of how post-disturbance management will impact ecological processes such as soil nutrient dynamics and stocks of soil carbon (C). The research in this dissertation focused on areas of widespread mortality in lodgepole pine (Pinus contorta var. latifolia) in northern Colorado due to the most recent outbreak of the endemic mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins). The goal of this research was to examine soil nitrogen (N) stocks, plant N uptake, and changes in forest soil C stocks in soil organic matter (SOM) due to tree mortality and subsequent salvage logging and from different belowground C inputs. To achieve this aim, I compared the three most prevalent management options: 1) uncut beetle-infested lodgepole pine stands and clear-cut salvage logged areas with either 2) post-harvest residue retention or 3) post-harvest residue removal. To determine the impacts of MPB-infestation and salvage logging on ecosystem N stocks and plant N uptake, I implemented an experimental field study by adding 15N-labeled ammonium sulfate to research plots centered over lodgepole pine seedlings. Measuring N stocks and 15N recovery in soil and vegetation pools over two growing seasons highlighted the coupled nature of forest C and N cycling between plant and soil forest ecosystem compartments. The majority of the 15N label was recovered in the soil and was not impacted by the management treatments. In contrast, the N uptake by lodgepole pine seedlings was driven primarily by the amount of C fixation and the patterns of C fixation, in turn, related to other environmental factors modulated by the management treatment, such as available light. An observational field study sought to quantify changes in forest soil C stocks in the bulk soil and SOM fractions and detect any changes in C chemistry as a result of management that may impact C persistence. In the dry, high elevation forests studied, soil C increased with salvage logging likely due to mixing of surface residues and O horizon C into the mineral soil during logging. The distribution of C stocks among the mineral soil fractions and the chemistry of those fractions indicated that root C accumulation in the particulate organic matter (POM, >53 μm) is an important mechanism of soil C accumulation in these forest soils. A mechanistic laboratory incubation evaluated the efficiency of mineral-associated organic matter (MAOM, <53 μm) formation from root and hyphal necromass inputs with different C chemistries. This study showed that rye root necromass with more labile and less structural C than pine roots, was processed most in the 38-day incubation and contributed much more efficiently to the formation of MAOM than did the pine roots. Despite less processing, the arbuscular and ectomycorrhizal fungal necromass both contributed as efficiently as rye roots to MAOM formation. These results indicate that both C chemistry and C/N ratio exert controls on residue processing and MAOM formation. Together, this dissertation work showed that salvage logging stimulated the growth of lodgepole pine seedlings, resulting in increased storage of both C and N in the plant biomass above- and belowground. As this pine root biomass turns over, the root necromass will contribute C to the POM fraction, the largest pool of soil C in this system. The net increase of forest soil C with salvage logging found in this study is notable as it suggests that the MPB-infested lodgepole pine forests of Colorado can be salvage logged with a low risk of significant soil C loss. Additionally, the highest recovery of the N label was in the soil, thus the high soil N recovery with higher soil C supports SOM is a sink of N reducing N losses. Finally, pine seedling colonization by ectomycorrhizal fungi may further aid with nutrient retention and the efficient formation of MAOM during regeneration.
Open Access
Forest structure in unharvested old-growth: understanding the influence of soils on variability of long-term tree dynamics and fire history
(Colorado State University. Libraries, 2013) Hasstedt, Steven C. M., author; Binkley, Dan, advisor; Rocca, Monique, committee member; Sibold, Jason, committee member; Martin, Patrick, committee member
Western North American forests adapted to frequent fires have been fundamentally altered and fragmented as a result of fire exclusion, the transportation infrastructure, development patterns, and other landscape level changes. In order to enhance the resiliency, diversity, and productivity of forest ecosystems it is essential to encourage collaborative, science-based restoration of forest landscapes and to develop a public understanding of the dynamic nature of forests. The USDA's Collaborative Forest Landscape Restoration Program (CFLRP) provides guidelines for community stakeholders and private advocacy groups to engage with federal, state, and local agency stewards to develop monitoring and assessment goals for forest restoration projects. The Uncompahgre Plateau (UP) was identified as one of ten initial CFLRP locations nationwide and has very large, old heritage trees scattered across never-harvested areas within the National Forest boundaries. Understanding how soil depth influences fire behavior and canopy development and determining the nature of historical fire regime on the UP are key elements for the development of local forest restoration prescriptions. Heritage trees appeared to occur more often on rocky soils, and I expected this could result from different fire behavior in landscape patches where soils are too thin to support dense forest cover and fuels. I tested the influence of soil depth on forest composition and the fire history of the study area in three phases. First, I recorded soil depth and site characteristics for 80 randomly selected plots and included targeted site sampling of all heritage trees (≥80 cm diameter) on two unroaded, never-harvested mesas to examine the relationship between soil depth, stand basal area, and the presence of heritage trees. The development of forest canopies (which influence fire regimes and tree survival) appeared to relate to soil characteristics (particularly rock cover). Single factor analysis revealed that soil depth alone only accounts for about 10% of stand basal area variation, but locations with soil > 30 cm deep had almost twice the basal area of locations with < 15 cm of soil depth. Comparing the observed to expected occurrence of heritage trees in four soil depth categories revealed a disproportionately greater presence of old-growth heritage trees on the locations with shallow soils. These results indicate that simple soil depth measurements can be used by restoration planners to develop stand-level spatial patterns. In the second phase, I used standard dendrochronology techniques to age trees from random plots, targeted heritage trees, and aspen transects to determine if historical stand structure patterns revealed forest age caps in concert with known landscape level historical fires. The spatial pattern of pre-1880 trees revealed that landscape level fires in the 1800s were likely not intense enough to kill all conifers over large areas, but were intense enough to kill most aspen stems on two of four sampled mesas. The mixed-severity nature of historical fires indicates that forest managers should have the leeway to plan for a spectrum of low to high severity fire effects within their restoration treatments. The third phase of my research tested the validity of my age-cap sampling methodology. I applied my sampling protocols to results from thirty systematic grid sampling locations composed of mixed conifer and spruce fir forests on the Kaibab Plateau, located on the North Rim of the Grand Canyon. My methodology targeted the largest trees and identified the oldest trees in the mixed conifer plots 97% of the time (in all but one plot). While a complete census of all trees would provide perfect information on the presence of an age cap, the validation of my targeted sampling approach provides a high confidence method to characterize the oldest trees in sampling locations with a substantial savings in the amount of time and resources expended. The subsequent ability to characterize the historical fire regime at the scale of the sampling design provides forest managers with another tool to inform restoration prescriptions. Applying the knowledge gained from the unroaded, never-harvested mesas to similar forest types on the Uncompahgre Plateau will guide landscape-scale treatment planning designed to restore ecosystem structure, composition, and function while reintegrating and managing wildfire as a natural component to reduce the risk of unnaturally severe crown fires.
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 member
The 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.
Open Access
How do ecological restoration treatments affect understory plant communities in dry conifer forests of the Colorado Front Range?
(Colorado State University. Libraries, 2022) Demarest, Arièl, author; Redmond, Miranda, advisor; Fornwalt, Paula, advisor; Rocca, Monique, committee member
Ecological restoration efforts are progressing in dry conifer forests across the western United States to increase resilience to fire and other disturbances. While such treatments primarily aim to create overstory change, impacts beyond the canopy should also be considered – such as effects on understory plants. Several studies have investigated outcomes of ecological restoration thinning treatments for understory plants, but few of these have examined effects across a landscape and at a time interval long enough for plants to potentially adjust to the disturbance. Additionally, none have investigated how specific aspects of treatment and local climate might interact to modify understory responses. In this study, we investigated the effects of ecological restoration thinning treatments on understory plant communities in dry conifer forests of the Colorado Front Range using a Before/After/Control/Impact study design. We collected data at 1-2 years pre-treatment, 1-2 years post-treatment, and 4-6 years post-treatment in 156 plots distributed across 8 sites, encompassing 15 treatment units and 15 nearby untreated areas. We found 1.6 times higher native understory plant cover and 1.1 times higher richness in treated compared untreated plots at 4-6 years after treatment. Heightened cover and richness values in treated plots were not driven by a single native plant functional group, but by a large portion of the community. Short- and long-lived, forb and graminoid, and vegetatively spreading and non-vegetatively spreading native plants all grew in cover. Both lifespans, forb, and non-vegetatively spreading native plants had heightened richness. Introduced plants showed 2.3 times higher cover and 3.9 times higher richness in treated plots compared to untreated, but were still present at very low levels. Greater native plant cover and richness were associated with lower basal areas that more closely resemble historical norms for the landscape. Thirty year average climatic water deficit (CWD) was not as strong of a predictor of native cover or richness as was a short-term relative measure, final spring CWD z-score, which describes how different the spring climatic conditions of the sampling year were from average conditions. Overall, the broad longer-term benefits to the native understory plant community that were found for numerous sites across the Colorado Front Range suggest that these results may generalizable to elsewhere on this and similar landscapes.
Open Access
Improving assessments of fuel treatment effects on surface fuels in ponderosa pine forests of the southern Rocky Mountains
(Colorado State University. Libraries, 2015) Vakili, Emma, author; Hoffman, Chad, advisor; Dickinson, Yvette, committee member; Keane, Robert, committee member; Rocca, Monique, committee member
Fuel hazard reduction treatments have been widely employed in dry forests of the western United States in recent decades in response to the increasing extent and severity of wildfires. In order to design and accurately assess the effects of these fuel hazard reduction treatments, accurate fuel inventories are required. However, obtaining accurate assessments of fuelbeds is complicated by a lack of knowledge about the effects of treatments on surface fuels and their spatial distribution. This thesis focuses on enhancing knowledge of treatment effects on surface fuels in ponderosa pine sites across Colorado and New Mexico, USA. The primary emphasis is on Chapter 1, which focuses on the spatial distribution of surface fuels and how it is changed by fuel hazard reduction treatments. I found that total surface fuel loads were reduced by ~10% in thinned sites and ~50% in thinned and burned sites. Semivariance following thin and burn treatments was similar to untreated sites and lower than thin-only sites for all fuel components except 1,000-hr fuels, with fuel component semivariance being highly predictable (R2=0.99) from fuel component mean fuel loading. The scale of spatial independence for all fuel components and sites ranged from <1-50 m with the shortest spatial scales occurring for the finest fuel components (i.e. duff, litter, etc.). Mean fuel particle diameter strongly predicted (R2=0.88) the distance needed to achieve sample independence. Incorporating such knowledge of spatial variability into fuel sampling protocols will enhance assessment of wildlife habitat and fire behavior and effects modeling over singular stand-level means. Chapter 2 focuses on the physical characteristics of fuel particles present before and after fuel hazard reduction treatments. I report mean squared diameter (d2) values for downed dead woody surface fuels that can be used to improve fuel loading assessments using the widely applied planar intersect sampling protocol. The planar intersect method requires an approximation of the mean squared diameter (d2) of 1, 10, and 100-hr timelag size classes to create loading estimates for downed dead woody surface fuels. I analyzed woody surface fuels collected throughout the southern Rocky Mountains to create local d2 estimates for untreated, mechanically treated, and mechanically treated and broadcast burned sites. Resulting estimates were up to 38% higher in the 1- and 10-hr classes and 28% lower in the 100-hr classes when compared to previously published values from other regions. The new burned partially harvested values for 1- and 100- hour classes were also roughly 20% lower than in the other stand conditions.
Open Access
Interactions and impacts of multiple bark beetle outbreaks in the southern Rocky Mountains
(Colorado State University. Libraries, 2022) Tutland, Niko Joseph, author; Hart, Sarah, advisor; Redmond, Miranda, committee member; Rocca, Monique, committee member
In conifer forests of western North America, outbreaks of native bark beetles are important biotic disturbances that influence forest structure and function. Subalpine forests in the southern Rocky Mountains (SRM) are home to multiple species of host-specific bark beetles that can affect the same stand concurrently or successively, potentially interacting to affect landscape patterns of tree mortality and subsequent disturbance dynamics. Despite their importance, the causes and consequences of interactions among bark beetle disturbances are poorly understood. To examine how outbreaks of different bark beetle species interact, we conducted two studies in the SRM. First, using broad-scale geospatial data, we explored the extent and severity of overlapping outbreaks of multiple bark beetle species across the SRM. We found that forest stand susceptibility to outbreaks of multiple bark beetle species is limited by host tree distributions, and that overlap of outbreaks was relatively uncommon. Furthermore, cumulative tree mortality was rarely higher in stands that experienced overlapping outbreaks compared to stands that experienced single-species outbreaks. These results suggest that forest trajectories in mixed-species stands will not be altered when multiple bark beetle outbreaks co-occur, compared to single-species outbreaks. Second, in a multi-scale study including both field and geospatial data, we explored how history of stand-replacing fires and a severe spruce beetle (Dendroctonus rufipennis) outbreak affected future susceptibility to subalpine fir (Abies lasiocarpa) decline (SFD) from outbreaks of the western balsam bark beetle (Dryocoetes confusus) and associated fungal pathogens. At the landscape scale, we found that disturbance history had limited effects on the susceptibility to future SFD, with a weak trend towards higher susceptibility in younger forests. At the stand scale, however, we found no effect of disturbance history on stand structure or composition traits that have been shown to influence susceptibility to SFD. Individual tree-scale analyses revealed that tree and local neighborhood traits were most important for determining likelihood of SFD. Weak connections between disturbance history, stand structure and composition, and SFD underscore the variability in forest recovery after disturbance, and highlight the need for future research. Together, these results from these studies indicate that, while climate change may be amplifying tree mortality events, subalpine forests in the SRM may be broadly resilient to co-occurring and successive disturbances.
Open Access
Magnificence in motion: climate and forest composition in Glacier National Park
(Colorado State University. Libraries, 2012) Urza, Alexandra, author; Sibold, Jason, advisor; Rocca, Monique, committee member; Binkley, Daniel, committee member
Worldwide climate is changing, resulting in inevitable shifts in ecosystems. Climate directly influences forest composition through effects on mortality, recruitment, and growth. Furthermore, disturbance can short-circuit the process of gradual species overturn in response to climate change. After a disturbance, current climate conditions may favor the establishment of species that were not historically dominant, accelerating ecosystem shifts. Whereas mature trees are generally resistant to minor environmental fluctuations, regeneration niches are often extremely sensitive to climate. While several studies have modeled climate envelopes associated with current species distributions, the climate conditions required for seedling establishment and growth may be more valuable indicators of potential species range shifts in response to climate change in disturbance-prone ecosystems. In this study, I examine the influence of post-fire climate on competition between two tree species in Glacier National Park (GNP). Western larch (Larix occidentalis) and lodgepole pine (Pinus contorta var. latifolia) are fire-adapted species that cohabit the subalpine zone of western GNP. Both species are shade intolerant, and extensive density-dependent mortality during canopy recruitment means that the seedlings that grow the fastest will be most likely to survive to the forest canopy. In Chapter One, I evaluate the use of terminal bud-scar counts for aging seedlings and measuring annual growth increments for four conifer species in GNP, including western larch and lodgepole pine. This analysis shows that terminal bud scars are reliably identifiable indicators of the location on the stem at which one year of growth ends and the next begins. Chapter Two examines the role of differential responses to site and climate in the coexistence of lodgepole pine and western larch in GNP. I used vertical growth measurements (distance between successive terminal bud scars) to develop Bayesian hierarchical models of seedling growth for each species. The results show that differential responses to environmental variability have historically promoted coexistence between these species. However, climate changes that increase disturbance frequency and move outside of the regeneration niches for these species may lead to a destabilization of their coexistence.
Open Access
Mapping burn severity, pine beetle infestation, and their interaction at the High Park Fire
(Colorado State University. Libraries, 2015) Stone, Brandon, author; Lefsky, Michael, advisor; Rocca, Monique, committee member; Leisz, Stephen, committee member
North America's western forests are experiencing wildfire and mountain pine beetle (MPB) disturbances that are unprecedented in the historic record, but it remains unclear whether and how MPB infestation influences post-infestation fire behavior. The 2012 High Park Fire burned in an area that’s estimated to have begun a MPB outbreak cycle within five years before the wildfire, resulting in a landscape in which disturbance interactions can be studied. A first step in studying these interactions is mapping regions of beetle infestation and post-fire disturbance. We implemented an approach for mapping beetle infestation and burn severity using as source data three 5 m resolution RapidEye satellite images (two pre-fire, one post-fire). A two-tiered methodology was developed to overcome the spatial limitations of many classification approaches through explicit analyses at both pixel and plot level. Major land cover classes were photo-interpreted at the plot-level and their spectral signature used to classify 5 m images. A new image was generated at 25 m resolution by tabulating the fraction of coincident 5 m pixels in each cover class. The original photo interpretation was then used to train a second classification using as its source image the new 25 m image. Maps were validated using k-fold analysis of the original photo interpretation, field data collected immediately post-fire, and publicly available classifications. To investigate the influence of pre-fire beetle infestation on burn severity within the High Park Fire, we fit a log-linear model of conditional independence to our thematic maps after controlling for forest cover class and slope aspect. Our analysis revealed a high co-occurrence of severe burning and beetle infestation within high elevation lodgepole pine stands, but did not find statistically significant evidence that infected stands were more likely to burn severely than similar uninfected stands. Through an inspection of the year-to-year changes in the class fraction signatures of pixels classified as MPB infestation, we were able to observe increases in infection extent and intensity in the year before the fire. The resulting maps will help to increase our understanding of the process that contributed to the High Park Fire, and we believe that the novel classification approach will allow for improved characterization of forest disturbances.