Net ecosystem production of two contrasting boreal black spruce forest communities

The objective of this study was to compare the carbon (C) budgets of two similar-aged boreal black spruce (Picea mariana [Mill.] BSP) forest communities: closed-canopy black spruce with feathermoss ground cover (BSFM) on moderately drained soils and open-canopy black spruce with Sphagnum ground cover (BSSP) on poorly drained soils. C content, soil surface carbon dioxide (CO2) flux (R-S), heterotrophic respiration (R-H), net primary production (NPP), and net ecosystem production (NEP) were measured or estimated. The total C content for the two communities (BSFM, 113 Mg C ha(-1); BSSP, 107 Mg C ha-1) did not differ significantly (P = 0.95). However, annual R-S was significantly greater (P < 0.0001) for the BSFM (564 g C m(-2) y(-1)) than the BSSP (319 g C m(-2) y(-1)) community. The greater R, in the BSFM (440 g C m(-2) y(-1)) than the BSSP community (264 g C m(-2) y-1) and the higher peat C content for the BSSP (84 Mg C ha(-1)) than the BSFM (34 Mg C ha(-1)) community provided evidence that the BSSP community had a lower decomposition rate than the BSFM community. NEP was significantly (P = 0.04) more negative for the BSFM community (-222 +/- 35 g C m(-2) y(-1)) than the BSSP community (-128 +/- 14 g C m(-2) y(-1)), but both communities were C sources to the atmosphere. The results from this study illustrate the influence of small differences in edaphic conditions on ecosystem C accumulation.