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 � 29-year-old) and a � 79-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 (MgCha � 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 (RS) with soil temperature to model annual RS for the stands (MgCha � 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 RH (where RH was calculated using a Monte Carlo approach as coarse woody debris respiration plus 30‐70% of total annual RS). Excluding C losses during wood processing, NEP (MgCha � 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.

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