Seasonal controls on patterns of soil respiration and temperature sensitivity in a northern mixed deciduous forest following partial-harvesting

FCO2 values from TL/BIO treatments exceeded unharvested controls, recurrently peaking in the autumn (average for TL/BIO: 28%/17%, p ⩽ 0.05) and waning in the summer (14%/10%, not significant). A comparison of measured FCO2 vs. modelled respiration values corrected for temperature differences indicated that higher soil temperatures following canopy thinning accounted for 34-41% of these differences in 2010 but <15% by 2012. Initially lower in 2010, Q10 and summer respiration values for harvested treatments exceeded those of controls by 2012, and despite waning temperature differences, average annual effect sizes corrected for temperature differences did not decline. Autumn and basal respiration rates were correlated with post-harvest fine woody debris volumes in 2010 (r2 = 0.58/0.57, p = 0.01), summer rates in all years decreased with harvested tree basal area (r2 = 0.43-0.58, p ⩽ 0.05), and the post-harvest basal area of understorey vegetation predicted increasing Q10 effect sizes from 2010 to 2012 (r2 = 0.81, p ⩽ 0.01). With consideration to studies demonstrating that the contribution of root respiration (RR) to FCO2 is highest in summer, we propose that partial harvesting initially restricts RR and peak summer respiration rates, but compensates for this decline by increasing basal respiration rates and FCO2 through elevated soil temperatures and decomposition rates from canopy thinning and harvest residue substrate inputs (i.e., woody debris and root necromass). During post-harvest recovery, forest understorey regrowth reduces soil temperatures but influences patterns of FCO2 by increasing summer respiration and Q10 values in harvested treatments, likely by increasing RR.