Low intensity prescribed fire and the fate of fire mobilized nutrients

The New Jersey pine barrens provides an excellent system for nutrient cycle investigations. The extensive upland forest plant communities exhibit low species diversity and the soils are primarily unconsolidated quartz sand deposits. To reduce the threat of wildfire, accumulated fuel loads are managed by low severity winter prescription fire. The underlying question of these investigations is: Will nutrients mobilized by burning of the organic layer in the upland forests be retained by physical or biological means or lost from the system due to leaching?; Through field, laboratory and greenhouse experiments I examined aspects of nutrient cycling; physico-chemical and biological mineralization, plant and microbial growth, and leaching loss as affected by prescription fire.; I found that moderate heating of litter, 300 °C, resulted in nitrogen volatilization losses of ca. 50%, whereas temperatures of 550 °C resulted in >99% nitrogen volatilization loss. Soluble phosphate and magnesium concentrations were found to significantly decline upon heating to 300 °C.; In spring, two months after prescription fire treatment, nutrient leaching loss was elevated, and subsequently declined to levels characteristic of an unburned site. One year after the application of a prescription fire treatment no difference was evident compared to an unburned site. Significant growing season leaching losses were seen, only for phosphorus and potassium, in treatment locations repeatedly burned. Field and greenhouse studies show that biological activity is influenced by and influences post fire soil conditions. Enhanced plant growth and reduced microbial activity are a consequence of burning.; Based on Boerner's research, my studies constitute the most comprehensive study of nutrients release from fire in this system. My results indicate that nutrients mineralized by prescription fire are primarily retained within the ecosystem by biological processes. No other study demonstrates that plant uptake of nutrients, following winter prescription fire, is the most important factor for nutrient retention, preventing significant leaching from the soil organic horizon. My results also indicate plant growth may be subject to fire induced limitation of phosphorus availability. Therefore the repeated use of prescription fire may negatively impact the system by reducing the size of the herbaceous layer and by reducing phosphorus availability.