Wednesday, November 15, 2006

Carbon and Nitrogen Dynamics Associated with Post-Wildfire Stand Development for Jack-Pine Dominated Sites in Northwestern Ontario.

Dave M. Morris, Laura Edgington, and Dan R. Duckert. Ontario Ministry of Natural Resources, c/o Lakehead Univ, 955 Oliver Rd, Thunder Bay, ON P7B 5E1, Canada

The objective of the current study was to document changes occurring to C and N stocks in relation to age since natural (wildfire) disturbance. A total of 15 sites, ranging in age since disturbance from 5 to 125 years, were selected from a broader plot array for the determination of C and N pools. As expected, total carbon storage increased substantially with stand age (140 to 300 T ha-1) , largely the result of carbon accumulations in tree biomass (0 to 90 T ha-1) and CWD (70 to 105 T ha-1). Soil carbon reserves also increased with stand age (60 to 100 T ha-1), due primarily to the build up of the forest humus layer (16 to 56 T ha-1). In contrast to C storage, only a small percentage (<10%) of the total N pool was associated with tree biomass during any age sequence. The largest store of N in these systems was in the mineral soil layers. There does appear to be a definite pattern of rapidly decreasing N soil reserves for nearly 20 years after wildfire (2900 kg ha-1 at age 5 to 1460 kg ha-1 by year 20), presumably resulting from increased N turnover, minimal plant uptake, and increased deep leaching. This decrease was, however, followed by an extended period of gradual increase in both the organic and mineral soil layers to a maximum reserve of 3600 kg ha-1 at year 90. In terms of available pool, N mineralization rates immediately after the fire peaked at 30 kg ha-1 yr-1, but dropped as stands approached crown closure (22 kg ha-1 yr-1), followed by a slight increase to a stable level of 25 kg ha-1 yr-1.