Effects of fire at two frequencies on nitrogen transformations and soil chemistry in a nitrogen-enriched forest landscape

This study reports results of the application of dormant-season prescribed fire at two frequencies (periodic (two fires in 4 years) and annual) at four southern Ohio mixed-oak (Quercus spp.) forest sites to restore the ecosystem functional properties these sites had before the onset of fire suppression and chronic atmospheric deposition. Each forest site comprised three contiguous watershed-scale treatment units: one burned in 1996 and 1999, one burned annually from 1996 through 1999, and an unburned control. Soil organic matter, available P, net N mineralization, and nitrification were not significantly changed by fire at either frequency, though values for the latter two properties increased 4- to 10-fold from the period 1995–1997 to the period 1999–2000. Fire at both frequencies resulted in increased soil pH and exchangeable Ca2+. Exchangeable Al3+ was reduced by fire at two of four sites, and the molar ratio of Ca/Al was increased by fire at three of four sites. In contrast to results in most studies ...