Soil surface COsub2/sub flux increases with successional time in a fire scar chronosequence of Canadian boreal jack pine forest

摘要

pstrongAbstract./strong To fully understand the carbon (C) cycle impacts of forest fires, both C emissions during the fire and post-disturbance fluxes need to be considered. The latter are dominated by soil surface COsub2/sub flux (iF/isubs/sub), which is still subject to large uncertainties. Fire is generally regarded as the most important factor influencing succession in the boreal forest biome and fire dependant species such as jack pine are widespread. In May 2007, we took concurrent iF/isubs/sub and soil temperature (iT/isubs/sub) measurements in boreal jack pine fire scars aged between 0 and 59 years since fire. To allow comparisons between scars, we adjusted iF/isubs/sub for iT/isubs/sub (iF/isubs/subsupT/sup) using a iQ/isub10/sub of 2. Mean iF/isubs/subsupT/sup ranged from 0.56 (± 0.30 sd) to 1.94 (± 0.74 sd) μmol COsub2/sub msup−2/sup ssup−1/sup. Our results indicate a difference in mean iF/isubs/subsupT/sup between recently burned (4 to 8 days post fire) and non-burned mature (59 years since fire) forest (iP/i & 0.001), though no difference was detected between recently burned (4 to 8 days post fire) and non-burned young (16 years since fire) forest (iP/i = 0.785). There was a difference in mean iF/isubs/subsupT/sup between previously young (16 years since fire) and intermediate aged (32 years since fire) scars that were both subject to fire in 2007 (iP/i & 0.001). However, there was no difference in mean iF/isubs/subsupT/sup between mature (59 years since fire) and intermediate aged (32 years since fire) scars that were both subjected to fire in 2007 (iP/i = 0.226). Furthermore, there was no difference in mean iF/isubs/subsupT/sup between mature (59 years since fire) and young scars (16 years since fire) that were both subjected to fire in 2007 (iP/i = 0.186). There was an increase in iF/isubs/subsupT/sup with time since fire for the chronosequence 0, 16 and 59 years post fire (iP/i & 0.001). Our results lead us to hypothesise that the autotrophicheterotrophic soil respiration ratio increases over post-fire successional time in boreal jack pine systems, though this should be explored in future research. The results of this study contribute to a better quantitative understanding of iF/isubs/sub in boreal jack pine fire scars and will facilitate meta-analyses of iF/isubs/sub in fire scar chronosequences./p.