Effects of logging on carbon dynamics of a jack pine forest in Saskatchewan, Canada

We calculated carbon budgets for a chronosequence of harvested jack pine (Pinus banksiana Lamb.) stands (0-, 5-, 10-, and similar to29-year-old) and a similar to79-year-old stand that originated after wildfire. We measured total ecosystem C content (TEC), above-, and belowground net primary productivity (NPP) for each stand. All values are reported in order for the 0-, 5-, 10-, 29-, and 79-year-old stands, respectively, for May 1999 through April 2000. Total annual NPP (NPPT) for the stands (Mg C ha(-1) yr(-1)+/-1 SD) was 0.9+/-0.3, 1.3+/-0.1, 2.7+/-0.6, 3.5+/-0.3, and 1.7+/-0.4. We correlated periodic soil surface CO2 fluxes (R-S) with soil temperature to model annual R-S for the stands (Mg C ha(-1) yr(-1)+/-1 SD) as 4.4+/-0.1, 2.4+/-0.0, 3.3+/-0.1, 5.7+/-0.3, and 3.2+/-0.2. We estimated net ecosystem productivity (NEP) as NPPT minus R-H (where R-H was calculated using a Monte Carlo approach as coarse woody debris respiration plus 30-70% of total annual R-S). Excluding C losses during wood processing, NEP (Mg C ha(-1) yr(-1)+/-1 SD) for the stands was estimated to be -1.9+/-0.7, -0.4+/-0.6, 0.4+/-0.9, 0.4+/-1.0, and -0.2+/-0.7 (negative values indicate net sources to the atmosphere.) We also calculated NEP values from the changes in TEC among stands. Only the 0-year-old stand showed significantly different NEP between the two methods, suggesting a possible mismatch for the chronosequence. The spatial and methodological uncertainties allow us to say little for certain except that the stand becomes a source of C to the atmosphere following logging.