Browsing by Author "Fornwalt, Paula, committee member"
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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 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 memberThroughout 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.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.