| dc.description.abstract | Decades of fire exclusion in historically fire-dependent forests across the southeastern U.S. have caused various ecological consequences, including the transition of open-structured forests to closed-canopy forests. This process involves the encroachment of often shade-tolerant, fire-sensitive, and/or opportunistic species, which leads to a decline in flammability, light availability, and subsequent replacement of shade-intolerant and/or fire-tolerant species. This phenomenon, known as mesophication, establishes a self-reinforcing feedback cycle in which the accumulation of encroaching vegetation further suppresses fire by creating cooler, moister understory conditions. Prescribed fire and mechanical thinning are often used to halt or reverse mesophication, though their effectiveness may vary. This dissertation comprises a series of studies examining the effects of mesophication on flammability, tree regeneration, functional mechanisms of persistence in competing hardwood species, and the effects of natural canopy disturbance on fuel characteristics and fire behavior. In the first study, we conducted experimental burns to evaluate how the progressive replacement of longleaf pine (Pinus palustris) by sweetgum (Liquidambar styraciflua) across a gradient of canopy cover affected fuelbed flammability, and survival and growth of species with different fire and shade tolerances. We found a significant reduction in flammability as the pine fuel component decreased below 30%, an effect that was further pronounced with increasing in canopy cover. Additionally, seedling survival was high regardless of species fire tolerance, with sweetgum exhibiting the highest survival across treatments and species. In the second study, we examined how above- and belowground traits of three hardwood species—red maple (Acer rubrum), sweetgum, and southern red oak (Quercus falcata)—responded to varying fire-return intervals and canopy structure. Our findings revealed higher trait plasticity in sweetgum, shown by shifts in non-structural carbohydrates and SLA, and a generalist strategy in red maple compared to southern red oak, regardless of fire frequency or canopy structure. In the third study, we assessed the influence of natural canopy disturbances such as hurricanes and natural tree mortality on fuelbed characteristics and fire behavior in two contrasting fire-dependent forest types: an upland hardwood forest and a longleaf pine woodland. Our results revealed significant effects of canopy loss on fuelbed characteristics in both forest types. Although canopy disturbances had no significant impact on fire behavior in the longleaf pine woodland, fire behavior in canopy gaps within the hardwood forest was more intense than non-disturbed areas. This dissertation contributes to a deeper understanding of the consequences of mesophication on forest flammability, explores functional mechanisms of encroaching species’ persistence, and informs our understanding of the effects of canopy disturbances on fuelbed characteristics and fire behavior across different fire-dependent forests. | en_US |
