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Abstract. 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 CO 2 flux (F s ), 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 F s and soil temperature (T s ) measurements in boreal jack pine fire scars aged between 0 and 59 years since fire. To allow comparisons between scars, we adjusted F s for T s (F T s ) using a Q 10 of 2. Mean F T s ranged from 0.56 (± 0.30 sd) to 1.94 (± 0.74 sd) µmol CO 2 m −2 s −1 . Our results indicate a difference in mean F T s between recently burned (4 to 8 days 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) and non-burned young (16 years since fire) forest (P = 0.785). There was a difference in mean F T s between previously young (16 years since fire) and intermediate aged (32 years since fire) scars that were both subject to fire in 2007 (P < 0.001). However, there was no difference in mean F T s between mature (59 years since fire) and intermediate aged (32 years since fire) scars that were both subjected to fire in 2007 (P = 0.226). Furthermore, there was no difference in mean F T s between mature (59 years since fire) and young scars (16 years since fire)Correspondence to: D. R. Smith (daniel.smith@nottingham.edu.my) that were both subjected to fire in 2007 (P = 0.186). There was an increase in F T s with time since fire for the chronosequence 0, 16 and 59 years post fire (P < 0.001). Our results lead us to hypothesise that the autotrophic:heterotrophic 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 F s in boreal jack pine fire scars and will facilitate meta-analyses of F s in fire scar chronosequences.

Abstract. 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 respiration (Rs), which is still subject to large uncertainties. This research investigates Rs in a boreal jack pine fire scar chronosequence at Sharpsand Creek, Ontario, Canada. During two field campaigns in 2006 and 2007, Rs was measured in a chronosequence of fire scars aged between 0 and 59 years since the last fire. Mean Rs per fire scar was adjusted for soil temperature (Ts) and soil moisture (Ms) (denoted RST,M). RST,M ranged from 0.56 μmol CO2/m2/s (32 years post fire) to 8.18 μmol CO2/m2/s (58 years post fire). The coefficient of variation (CV) of RST,M ranged from 20% (16 years post fire) to 56% (58 years post fire). Across the field site, there was a statistically highly significant exponential relationship between Rs adjusted for soil organic carbon (Cs) and Ts (P<0.00001; Q10=2.21) but no effect of Ms on Rs adjusted for Cs and Ts for the range 0.21 to 0.77 volumetric Ms (P=0.702). RST,M decreased significantly (P=0.030) after fire (4 to 8 days post fire) in mature forest, though no significant (P>0.1) difference could be detected between recently burned (4 to 8 days post fire) and unburned young forest. There were significant differences in RST,M between recently burned (4 to 8 days post fire) scar age categories that differed in their burn history, with between-fire intervals of 32 vs. 16 years (P<0.001) and 32 vs 59 years (P=0.044). There was a highly significant exponential increase in RST,M with time since fire (r2=0.999; P=0.006) for the chronosequence 0, 16 and 59 years post fire, and for all these age categories, RST,M was significantly different from one another (P<0.05). The results of this study contribute to a better quantitative understanding of Rs in boreal jack pine fire scars and will facilitate improvements in C cycle modelling. Further work is needed in quantifying autotrophic and heterotrophic contributions to Rs in jack pine systems; in monitoring Rs for extended time periods after fire; and in measuring different fire-prone forest types.