Browsing by Author "Stevens-Rumann, Camille S., committee member"
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Item Open Access Laboratory evaluation of a post-fire ground treatment to mitigate soil erosion and runoff(Colorado State University. Libraries, 2018) Moden, Kayla Nicole, author; Bareither, Christopher A., advisor; Scalia, Joseph, IV, committee member; Stevens-Rumann, Camille S., committee memberThe objective of this study was to assess the efficacy of using agricultural straw mulch as a post-fire ground treatment to mitigate soil erosion and runoff. A laboratory research program was carried out to measure soil erosion and runoff in a physical slope-model experiment (surface dimensions = 76 cm long x 30 cm wide). Intact block samples were collected that represented conditions in Colorado wildfire prone areas. The vegetation on select block samples was burned to simulate a high-intensity wildfire. Unburned block samples with varying amounts of vegetation and burned block samples with varying amounts of straw mulch (0, 0.06, 0.11, and 0.22 kg/m2) were tested in the slope-model experiment at a slope of 28o under a simulated rainfall of 48 mm/h for 40 min. Burned block samples were exposed to two rainfall simulations conducted three days apart to explore changes in soil hydraulic properties due to potential soil crust formation. Runoff, and eroded sediment were collected during simulated rainfall, and intact subsamples were collected from unburned and burned block samples after the rainfall simulations to evaluate the effects of high severity burning on physical characteristics and hydraulic and mechanical properties (i.e., dry density, total organic carbon, hydraulic conductivity, water repellency, and shear strength). Burning exponentially increased erosion compared to unburned conditions and all rates of straw mulch reduced soil erosion to levels consistent with unburned samples. Runoff and erosion increased with a decrease in natural surface vegetation on unburned samples and increased with a decrease in straw mulch applied to burned samples. Notable changes in geotechnical properties with high severity burning were not found in this study, which suggested that the observed increase in erosion on bare burned samples during rainfall simulations was attributed to destruction of surface cover with burning.Item Open Access Seeing the forest for the seeds: masting and mortality in dry forest and woodland ecosystems of the Rocky Mountains and Colorado Plateau(Colorado State University. Libraries, 2022) Wion, Andreas P., author; Redmond, Miranda D., advisor; Pearse, Ian S., committee member; Stevens-Rumann, Camille S., committee member; Rocca, Monique E., committee memberFor forests to persist on the landscape, tree recruitment must keep pace with tree mortality. Larger, more frequent, and more severe disturbances have raised concerns about the capacity for water-limited forests and woodlands to recover under increasingly hotter climates. For most conifer species, seed availability is the fundamental prerequisite to new tree recruitment. In addition, most conifer species are also masting species, meaning seed production is highly variable among years and synchronous within a population. Masting creates boom and bust patterns of seed availability that shape forest dynamics. In many species, it remains unknown what drives masting or how the mosaic of climate and competition shape patterns of seed production across species ranges. This limits our ability to forecast forest demography across large spatial areas and under uncertain climate futures. This dissertation is an exploration into two key processes driving forest persistence and loss, mast seeding and tree mortality, in two pine species native to dry forests and woodlands of the Rocky Mountains and Colorado Plateau: piñon pine and ponderosa pine. In chapter one, I examine the spatiotemporal drivers of masting in piñon pine across its latitudinal distribution in Colorado and New Mexico. I demonstrate that masting was driven by favorable weather conditions acting during key phenological periods of cone development: initiation and pollination. Cone production was sensitive to the spatial variability in long-term climate - cooler and wetter sites produced more cones, more frequently than hotter and drier sites. In chapter two, I examined cone production in ponderosa pine across a large portion of this species' distribution between Arizona and Wyoming. In contrast to piñon pine, I found that individual-level factors like tree size, age, and stand density, were better predictors of cone production than long-term climate or annual weather. In chapter three, I examined patterns of cone production between these two species jointly and related them to large scale modes of climate variability, like the North American monsoon and the El Niño Southern Oscillation. I found similar patterns, where piñon pine cone production was strongly associated with climate while ponderosa pine was not. Range wide synchrony in masting was associated with the North American monsoon, and regional north-south anti-synchrony was associated with the phase of the El Niño Southern Oscillation. Collectively, these chapters highlight contrasting masting patterns among these two, co-occurring pine species of dry forests and woodlands of the Rocky Mountains and Colorado Plateau. I explore the consequences of these contrasting life history strategies for forest management in this region, as well as the potential impacts of a changing climate and disturbance regime on seed production. In the final chapter of this dissertation, I evaluated four drought metrics on their ability to correctly predict piñon pine die-off following a severe drought in 2018. The results highlight how some of these simple climate metrics can be used as an indicator of piñon pine die-off in future, hotter drought events, and I provide a simple framework for evaluating mortality risk at regional scales.Item Open Access The role of disturbance and local adaptation in altering tree regeneration responses to climate change(Colorado State University. Libraries, 2023) Nigro, Katherine M., author; Redmond, Miranda D., advisor; Battaglia, Michael A., committee member; Stevens-Rumann, Camille S., committee member; Rocca, Monique E., committee memberAnthropogenic climate warming is predicted to reorganize the communities seen on the landscape today as species migrate to stay within their preferred climate niche. However, for long-lived trees, it is uncertain whether migrations will be able to keep pace with the rapidly changing climate. In addition, adaptations to local climate that have evolved within subpopulations of a species may become obsolete or maladaptive under climate change. Natural disturbances such as wildfire and insect outbreaks in forests may help to accelerate range shifts by reducing competition from other plant species and creating favorable microsites for establishment of novel species. For landscapes that are not recovering after disturbance events, human-assisted movement of populations within species (assisted gene flow) has been proposed to pre-adapt the forest to future climate conditions. In the first part of my dissertation, I analyze large-scale USDA Forest Service Forest Inventory and Analysis data from the interior western US and conduct a field study of trembling aspen in southern Colorado to understand how disturbances are interacting with climate change to alter species range shifts at broad and local scales. The first chapter of my dissertation shows that disturbances are catalyzing range shifts on a large-scale for the dominant tree species of the interior western US under both disturbed and undisturbed conditions, but mostly through reduced regeneration in hot and dry portions of species ranges rather than expansions into cooler and wetter areas. However, chapter 2 reveals that expansions are happening on more local scales for trembling aspen after wildfire, but not after beetle-kill mortality events. Therefore, this research shows that disturbance-facilitated species range expansions are limited to certain species and locations, which may not be enough to keep pace with climate warming. The second part of my dissertation investigates the potential for assisted gene flow in ponderosa pine by examining differences between seedlings from different populations and mother trees in both the greenhouse under drought and the field under a variety of microsite conditions. This research reveals that population climate and watering regime are important determinants of seedling growth in the greenhouse, but that ponderosa pine seedlings from hotter and drier populations do not possess adaptations typically associated with drought-tolerance and do not perform well when planted at the cooler range margin. In addition, mother tree sensitivity to climate was influential in seedling water use efficiency in the greenhouse and in the sensitivity of seedlings to microclimate conditions in the field, making the case that targeting seed collections from specific mother trees may be warranted. Overall, my dissertation research provides insight into how future disturbance events are likely to influence regeneration at species range margins and provides valuable information for land managers seeking to implement assisted gene flow at the upper elevational margin of ponderosa pine forests.