PARENT SESSION
Poster Session #19: Nutrient Cycling.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall

Does clearcutting alter the abundance of soluble organic nitrogen in forest soils?

Hannam, Kirsten¹, Prescott, Cindy¹, ¹

ABSTRACT- The distribution of soluble organic nitrogen (SON) in forest soils and the impact of clearcutting on this nitrogen pool are not well-understood. To address this, soil was collected through the growing season from three clearcuts and three uncut controls in a high-elevation spruce/fir forest and a coastal cedar/hemlock forest in British Columbia, Canada. In the coastal forests, only forest floor was collected; in the high-elevation forests, where forest floor is thin, both humus and underlying mineral soil were sampled. Extracts (1M KCl) were analyzed for nitrate, ammonium and SON (after persulfate oxidation). Water extracts of a subset of the samples were analyzed for amino acid content using HPLC. In the uncut forests at both sites, SON was consistently more abundant than mineral-N in all soil types and on all sampling dates. Treatment differences in the concentration of SON were small in the coastal forest soils. In the high-elevation forests, SON concentrations were lower and mineral-N concentrations higher in soil from the clearcuts. Higher amino acid concentrations were measured in soil from the uncut forests at both sites. These results indicate that timber harvesting alters the chemistry and quantity of SON in some forest soils. Since the mechanisms behind these treatment effects (ex. plant uptake, microbial turnover, abiotic chemical/physical processes) have not been determined, the implications for forest regeneration are unclear.

KEY WORDS: organic nitrogen, amino acids, clearcutting, forest soils