This Is AuburnElectronic Theses and Dissertations

Prescribed Fire Effects on Soil Properties and Nutrient Dynamics in a Longleaf Pine Forested Wetland Watershed




Molina Serpas, Lidia

Type of Degree

Master's Thesis




In a geographically isolated wetland (GIW) area, located in Georgia, longleaf pine forests have been experiencing frequent rotational prescribed burning for more than 10 years. In general, because wetlands provide ecosystem services, such as sediment retention and nutrient storage, it is important to understand how fire can alter biogeochemical processes. Previous research has shown that prescribed fires can release nutrients, alter soil properties, and modify soil moisture dynamics. Prescribed fire effects to Longleaf pine forests have been documented in the Southeast, but few have investigated effects to forested GIWs. These studies generally focus on prescribed fire impacts to water quality. In comparison, this research studies the effects of prescribed fire on hydrological properties, soil properties, nutrient movement, as well as carbon and nitrogen isotopic ratios to further understand immediate (short-term) changes in surface and subsurface horizons as well as chronic (long-term) impacts along a low-relief hillslope where there is a transition from forest to wetland. The main objectives of this research were to: (1) document soil moisture alterations immediately after prescribe fire, in the surface horizon, (2) determine whether or not prescribed fire can increase vertical nutrient movement with depth in a soil profile over short time scales, and (3) identify the immediate and chronic effects prescribed fire will have on nutrient concentrations and carbon and nitrogen isotopic ratios in surface and subsurface soil horizons. Two forested GIW watersheds at the Jones Center at Ichauway, GA were selected for study. Both are managed with prescribed burns bi-annually, one burned during the study (immediate site) and one burned the year prior (chronic site). Sampling was conducted before the prescribed fire, after the prescribed fire, and after a large rain event. Two-way ANOVA analysis and unpaired t-tests show no significant short-term changes to hydrological properties, but shortly after the fire, hydrophobicity increased promptly after the fire in all sampling points but only remained high on the hillslope after the rain event contrary to the expected decrease in hydrophobicity with increasing soil moisture. There were no prominent effects to soil texture and bulk density immediately after the prescribed fire or after the rain event. There were observable temporal changes to nutrient concentrations in surface and subsurface horizons and we found a positive correlation existing post-fire. The expressed significant differences in the horizons and the higher nutrient levels found in the chronic site is potentially caused by the addition of ash into the system overtime. In our immediate site, there were nutrient (total C, P, Mg, K, Ca, and Mn) increases found along the wetland edge. Also after the large rain event, total Al and Fe concentrations increased in subsurface horizons at the immediate site suggesting a fire signature. There were no significant temporal changes to carbon and nitrogen isotopic signatures despite finding some enrichment. Overall, a prescribed fire may cause immediate effects to hydrological properties, but it can also lead to chronic impacts due to the observed alterations to soil properties and nutrient dynamics. This work shows that short-term and long-term effects are difficult to resolve and specific impacts to soil nutrient cycling requires more study.