Short- and Long-Term Effects of Fire on Nitrogen Cycling in Oak Savanna Restoration Areas
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Oak savanna habitats are integral parts of Midwestern landscapes that are strongly regulated by fire and nutrient cycling. Due to the recent decline in the total area of undisturbed oak savanna habitats, information on nutrient cycling and the long-term and short-term effects of fire in oak savanna is invaluable for restoration efforts. Fire affects the distribution of oak savanna as well as nutrient cycling and nutrient availability. In this study, N mineralization rates, N availability, pH, and soil temperature in long-term bum sites and in short-term oak savanna restoration sites were examined. Principle component analysis separated study sites on the basis of bum frequency and logging history. Long-term plots with high bum frequency exhibited warm soils, high pH, high initial NH4 values, low NH4 and N03 availability and low N mineralization rates. Plots with low fire frequency exhibited low soil temperatures, low pH, low initial NH4 concentrations, high N03 and NH4 availability, and high N mineralization rates. Oak savanna restoration plots exhibited warm soils, high pH, high initial NH4 concentrations, high levels of NH4 and N03 availability, and high N mineralization. Frequent fire reduces the concentration of nutrients returned to the soil and kills the nitrifying bacteria, which increase N mineralization rates. This explains why study sites with a high frequency of fire had low N availability and N mineralization and sites with a low frequency of fire had high N availability and N mineralization. Sites with bum frequencies, N mineralization and N availability readings in the middle of the spectrum proved to be the most successful at supporting the oak savanna ecosystem in the long run. More information on the effects of fire frequency and N mineralization and N availability in oak savanna habitats and is needed to devise successful techniques for oak savanna restoration.