Browsing by Author "Rocca, Monique, advisor"

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Open Access
Lodgepole pine regeneration after mountain pine beetle and wildfire: a case study in the High Park Fire, CO
(Colorado State University. Libraries, 2016) Wright, Micah, author; Rocca, Monique, advisor; Rhoades, Charles, committee member; Hoffman, Chad, committee member
The 2012 High Park Fire burned over 35,000 hectares, including 5,000 hectares of lodgepole pine (Pinus contorta) forest that had recently been attacked by mountain pine beetle (MPB, Dendroctonus ponderosae). This sequence of events provided an excellent opportunity to investigate the effects of combined disturbance on lodgepole pine regeneration trajectories. I examined the influence of MPB mortality, high canopy fire severity, site characteristics, and post fire mulching treatments on lodgepole pine recovery at both landscape (∼hectare) and fine (∼cm) spatial scales. At the landscape scale, lodgepole pine seedling densities varied from 240 to 470,000 stems/ha. Seedling densities decreased as MPB mortality and high canopy fire severity increased. At the fine scale, lodgepole pine seedling establishment was positively related to local cone abundance and negatively related to high canopy fire severity. Topographic variables such as aspect and elevation did not have a strong influence on seedling density or establishment at either scale, nor did competition from recovering vegetation have an influence at the fine scale where it was considered. In areas with high canopy fire severity, post-fire straw mulching treatments were positively related to seedling establishment, indicating that mulching treatments may have additional benefits beyond erosion control. My research demonstrates that combinations of pre-fire mountain pine beetle mortality and high canopy fire severity can affect lodgepole pine regeneration, and may drive heterogeneity in the post-fire landscape.
Open Access
Spatial and temporal controls on pinyon and juniper seedling establishment in the Uncompahgre Plateau, western Colorado
(Colorado State University. Libraries, 2012) Graeve, Phillip Jay, author; Rocca, Monique, advisor; Brown, Peter, committee member; Sibold, Jason, committee member
Moderate and extreme climate events have the potential to cause sudden shifts with long-lasting relictual effects in ecological communities. In this study I investigated the direct and indirect effects of climate on Colorado pinyon (Pinus edulis) and Utah juniper (Juniperus osteosperma) on the Uncompahgre Plateau in western Colorado. I determined age structure of pinyon seedlings and tested for the effects of current year and antecedent year climate on seedling establishment. Finally, I described microhabitat preferences (substrate microhabitat and overstory canopy) for pinyon and juniper seedlings and assessed whether suitable microhabitats may have changed as a consequence of overstory die-off. No relationships between climate and pinyon establishment were detected, and pinyon establishment appears to have been relatively constant over the past 30 years. I found that both pinyon and juniper exhibited distinct preferences for certain substrate microhabitats, especially different types of litter. Pinyon seedlings avoided bare soil microhabitats. While both pinyon and juniper seedlings avoided open overstory microhabitat, pinyon preferred juniper overstory microhabitat. Microhabitat preferences of pinyon seedlings may buffer seedlings from climate-induced stress. Pinyon overstory declined rapidly due to a severe drought from 2000-2004, but juniper overstory was not affected. My results indicate that episodic overstory mortality events and continuous pinyon establishment characterize pinyon dynamics on the Uncompahgre Plateau, at least within the 30 year time frame investigated here. In contrast, juniper seedlings are less abundant but likely more resilient to climate-induced changes in microhabitat structure. Future pinyon establishment and overstory survival may be reduced due to direct and indirect effects of climate, especially if predictions for increased drought frequency and severity for this area are realized.
Embargo
Subalpine seed dispersal capacity: understanding the role of disturbance adjacency in the context of post-fire recovery
(Colorado State University. Libraries, 2024) Crosby, Brynn, author; Rocca, Monique, advisor; Aplet, Gregory, committee member; Knapp, Alan, committee member; Fornwalt, Paula, committee member
There is a growing concern about the ability of forest systems to recover following recent large, high-severity wildfires. While such fires are a natural part of subalpine forests in the Southern Rockies, a warming climate and the interaction between wildfires and recent bark beetle outbreaks may be challenging forest resilience (the ability to return to pre-fire conditions). Seed production and dispersal – a critical process that mediates landscape recovery – is not yet well understood for systems having been impacted by beetle-kill, but is expected to decline. Therefore, the purpose of this research is to identify how a bark beetle outbreak in adjacent, unburned subalpine forest surrounding a high-severity burn patch shapes seed dispersal following a wildfire. Specifically, this study aims to understand how spruce beetle-kill and forest characteristics may influence seed production of Picea engelmannii (Engelmann spruce) in the unburned edge of wildfire and subsequent seed dispersal into a burned patch. In the summer of 2022, I installed 275 seed traps and quantified seed dispersal into high severity burn patches of the 2020 Cameron Peak Fire. I fit a series of Bayesian statistical models to estimate the role that spruce beetle severity and other characteristics of the unburned forest edge explained Engelmann spruce seed production and dispersal distance. Site beetle severity ranged from 6% beetle related mortality to 92% beetle related mortality. However, I found no evidence that this mortality had any significant influence on the quantity of seed collected or the distance seeds dispersed. Seeds were collected at all trap installation distances of every site burn patch, with roughly 3.3 Engelmann spruce seed per trap. There was no statistical difference between the average seed collected at each trap installation distance, meaning that the average quantity of seed collected at 15m from the unburned edge was not statistically different than the average seed collected at 100m from the unburned edge across sites. These findings suggest that spruce beetle kill does not necessarily have a limiting effect on seed production and seed dispersal as would be expected. In years of high seed production for Englemann spruce, forest characteristics which may commonly limit seed dispersal (e.g. tree height, slope, tree age, etc.) may have less of a limiting effect.