Effects of Fire on Nitrogen in Forest Floor Horizons

Abstract The effects of burning no nitrogen (N) losses and transformations in red pine ( Pinus resinosa Ait.), eastern hemlock [ Tsuga canadensis (L.) Carr.], and Douglas‐fir ( Pseulotsuga menziesii )/western larch ( Larix occidentalis Nutt.) forest floor were investigated. Organic horizon samples were burned at 400°C for 30 min in a top‐heating oven to simulate field conditions. Measurements taken immediately after burning showed total and available N losses from the O 1 horizons but gains in total and available N in underlying layers. After burning, the litter was incubated for 5 weeks and analyzed for ammonium and nitrate concentrations and changes in acidity. Each forest floor type displayed varying patterns of ammonification, nitrification and immobilization of N. The N changes appeared related to the differing initial N contents of the organic material.