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Soil respiration in a fire scar chronosequence of Canadian boreal jack pine forest

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journal contribution
posted on 27.10.2009, 14:53 by D.R. Smith, Jörg Kaduk, Heiko Balzter, M.J. Wooster, G.N. Mottram, T.J. Lynham, J. Studens, J. Curry, G. Hartley, B.J. Stocks
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.



Biogeosciences Discussions, 2009, 6 (5), pp. 8725-8773.

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