PARENT SESSION
Symposium #5: Sustaining and restoring our soil.
Sponsored by ESA Soil Ecology Section
Organized by: S.M. Adl. and S. Morris.
Monday, August 6, 2001. 1:00 PM to 4:50 PM. Madison Ballroom A

Is prescribed fire effective in restoring eastern forest soils under heavy atmospheric N loading?

Boerner, Ralph¹, ¹

ABSTRACT- The oak-hickory forests of eastern North America have been subjected to effective fire suppression and heavy atmospheric deposition for most of a century. This has resulted in increase in both organic and inorganic N in forest floor and soils, as well as lowered soil pH and Ca:Al ratio. As part of a larger ecosystem restoration experiment we subjected watershed-scale treatment units to spring fires at two frequencies (1996+1999 and annually from 1996 to 1999). Losses of N through direct volatilization from forest floor fuels during fires were small compared to annual atmospheric inputs. Spring/early summer N mineralization and nitrification have increased in burned plots, due both to microclimate alteration and changes in organic matter quality. Semivariance analysis indicates that spatial structure has increased and patch size has decreased with increasing fire frequency. Soil organic C content has changed little, but organic matter quality, as indicated by soil enzyme activity patterns, has decreased. Summer acid phosphatase and -glucosidase activities are lower in soils of burned than control plots, whereas phenol oxidase activity is higher in burned than control plots. Burning has increased soil pH 0.3-0.7 units, depending on landscape position. Our burning treatments were only modestly effective in restoring forest soils to the conditions we believed existed prior to the onset of fire suppression and atmospheric deposition.

KEY WORDS: restoration, deciduous forest, N mineralization, soil enzyme activity