Temporal and spatial changes in soil carbon and nitrogen after clearcutting and burning of an old-growth Douglas-fir forest.

Abstract

We used 135 permanent plots (4 m²) nested within 15 blocks (121 m²) to quantify changes in concentration and spatial variation of carbon (C) and nitrogen (N) in the mineral soil (0- to 10-cm depth) after logging and broadcast burning of an old-growth, Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forest. Before harvest, surface soils averaged total C of 7.2 percent, total N of 0.19 percent, extractable NH₄ +-N of 5.2 µg/g, extractable NO₃ —N of 0.19 µg/g, and pH of 5.3. Samples collected 9 months after burning showed a 26-percent decline in concentration of total C, but a 5-percent increase in concentration of total N. Concentrations of extractable mineral N (NH₄ +-N + NO₃ —N) increased to five time initial levels but returned to preharvest levels 1 year later. The coefficient of variation in extractable mineral N more than doubled after burning. Two and 3 years after burning, extractable N showed a significant and increasingly strong negative relation with plant biomass suggesting that N concentration was measurably reduced by plant uptake. Most variation in soil C and N before harvest occurred at small spatial scales (within and among 2- by 2-m plots); logging and broadcast burning had little effect on this pattern.

Citation

Antos, Joseph A.; Halpern, Charles B.; Miller, Richard E.; Cromack, Kermit, Jr.; Halaj, Melora G. 2003. Temporal and spatial changes in soil carbon and nitrogen after clearcutting and burning of an old-growth Douglas-fir forest. Res. Pap. PNW-RP-552. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 19 p