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

摘要

To fully understand the carbon (C) cycle impacts of forest fires, both Cemissions during the fire and post-disturbance fluxes need to be considered.The latter are dominated by soil surface CO₂ flux (F_s), which isstill subject to large uncertainties. Fire is generally regarded as the mostimportant factor influencing succession in the boreal forest biome and firedependant species such as jack pine are widespread. In May 2007, we tookconcurrent F_s and soil temperature (T_s) measurements in borealjack pine fire scars aged between 0 and 59 years since fire. To allowcomparisons between scars, we adjusted F_s for T_s (F_sT)using a Q₁₀ of 2. Mean F_sT ranged from 0.56 (± 0.30 sd)to 1.94 (± 0.74 sd) μmol CO₂ m−2 s−1. Our resultsindicate a difference in mean F_sT between recently burned (4 to 8days post fire) and non-burned mature (59 years since fire) forest (P < 0.001), though no difference was detected between recently burned(4 to 8 days post fire) andnon-burned young (16 years since fire) forest (P = 0.785). There was adifference in mean F_sT between previously young (16 years sincefire) and intermediate aged (32 years since fire) scars that were bothsubject to fire in 2007 (P < 0.001). However, there was no difference in meanF_sT between mature (59 years since fire) and intermediate aged (32 years sincefire) scars that were both subjected to fire in 2007 (P = 0.226).Furthermore, there was no difference in mean F_sT between mature (59 years sincefire) and young scars (16 years since fire) that were both subjected to firein 2007 (P = 0.186). There was an increase in F_sT with time sincefire for the chronosequence 0, 16 and 59 years post fire (P < 0.001). Ourresults lead us to hypothesise that the autotrophic:heterotrophic soilrespiration ratio increases over post-fire successional time in borealjack pine systems, though this should be explored in future research. Theresults of this study contribute to a better quantitative understanding ofF_s in boreal jack pine fire scars and will facilitate meta-analyses ofF_s in fire scar chronosequences.