Fire ecology

Mixed conifer forests in the Sierra Nevada, California, face threats from frequent highseverity fire associated with climate change and fuel accumulation leading to vegetation shifts at local and landscape scales. Under rapid climate change, a clear understanding of how vegetation responds to single and/or repeated wildfires is still lacking and needs to be investigated. Using field and satellite data, the effects of wildfire on vegetation dynamics were explored at the plot and landscape levels in this dissertation project. Results from the field data suggest that management activities may be required in high-severity burned areas to restore dominance of mixed conifer forests and regain historical species composition in areas where live trees persist. Results from satellite data suggested that large shrub patches, created after mixed severity fire, fragment the homogenous mixed conifer dominated forest of the Sierra Nevada to create a more heterogeneous landscape, however the extent of diversity and fragmentation were dependent on fire severity and scales. Natural wildfires may restore landscape heterogeneity to conditions equivalent to the pre-Columbian era, but effects under the projected climate change scenario for 21st century remain uncertain. Mixed conifer dominated forests are predicted to be the dominant component of the Sierra Nevada landscape under historical fire probabilities and excluding higher probability of high-severity fire over the next 100 years.

Fire is a tool to reduce fuel and restore ecosystems but poses a risk of peat combustion that temporally restricts managers. Studies indicate that fires may be prescribed with a water table lower than the peat surface, but are based on locations with different peat properties or assumed heat inputs. The goal of this research is to quantify peat surface heating during a passing fire and the heat required to ignite peat under lowered water tables. This study used temperature probes at two heights to quantify peat surface heating during a prescribed fire and a manipulative experiment to quantify the effects of water table recession on peat properties important for predicting ignition. The soil surface experienced 87% of the flaming heat in sawgrass dominated areas. The heat required to ignite the peat surface was significantly correlated with the water table depth. This provides managers greater opportunity for prescribing fire.

Fire occurrences in the Everglades have increased since hydrologic alterations began, yet the vulnerability of Everglades peat to combustion during wildfires has yet to be determined. Natural fire regimes help maintain ecosystem functions and services and disruptions of natural disturbance regimes can have detrimental impacts, jeopardizing ecosystem health. Severe peat combustion can destroy native vegetation, alter microtopography, and release large amounts of stored carbon into the atmosphere. To create a better understanding of the mechanistic controls on Everglades ground fires, the soil's physical properties within several sites of Water Conservation Area 3 and how changes in water table affect these physical characteristics were determined. Areas disturbed by hydrologic alterations contain higher mineral content and therefore require lower water content to combust when compared to preserved regions. Changes in water tables have a significant effect on soil moisture and lower water tables drastically increase the vulnerability of a region.