Date of Award
Summer 6-29-2023
Degree Type
Thesis
Degree Name
Master of Science in Integrative Biology (MSIB)
Department
Biology
Committee Chair/First Advisor
Heather D Alexander
Major Professor
Matthew P Weand
Second Committee Member
Mario Bretfeld
Third Committee Member
Nicholas S Green
Abstract
Longleaf pine (LLP) ecosystems have experienced a widespread ecological state shift largely due to fire exclusion which has allowed mesophytes, i.e., shade-tolerant, often fire-sensitive species to encroach, reducing flammability and biodiversity through a process known as “mesophication.” Although prescribed fire is commonly used to reverse mesophication, fire behavior, and thus prescribed fire utility for this purpose, is poorly characterized in mixed pine-hardwood stands with mesophyte encroachment. This study aimed to identify mechanisms by which tree composition, structure, and fuels contribute to fire behavior, focusing on the understudied mountain longleaf pine (MLLP) ecoregion in northwest Georgia. I hypothesized that woody vegetation composition and structure indirectly influence fire behavior through fuel bed traits. Relative decreases in basal area and increases in the relative importance of pine and pyrophytic hardwoods (e.g., Quercus spp.) were expected to increase fuel load and reduce bulk density, thereby increasing fire rate of spread (RoS), fuel consumption, and residence time. To test this, I collected fuel and fire data across a gradient of woody vegetation composition and structure during dormant season prescribed burns and used Bayesian path analysis to estimate the effects of vegetation, fuel traits, and weather on fire. Results showed that the canopy directly influenced fire behavior but lacked significant indirect effects through fuel bed traits. Despite lacking a significant relationship with the canopy, greater fuel bed bulk density significantly reduced RoS and duff consumption. Precise mechanisms remain unresolved, but increased mesophyte importance directly and indirectly reduced fire intensity, in part by reducing available fuel load, and should be targeted for removal in restoration efforts. In contrast, pyrophytic hardwoods significantly increased fire intensity in MLLP.