Soil respiration and controls in warmer winter: A snow manipulation study in postfire and undisturbed black pine...

Climate change impacts drive warmer winters, reduced snowfall, and forest fires. In 2020, a wildfire scorched about 1508 hectares of black pine (Pinus nigra Arnold) forests in Türkiye. Whether the combined effects of lack of snow and forest fires significantly alter winter soil respiration (R_s) and soil temperature remains poorly understood. A field experiment was conducted in the postfire and undisturbed black pine forests during the winter to quantify R_s rates as affected by lack of snow and forest fire. We applied four treatments: snow-exclusion postfire (SEPF), snow postfire (SPF), snow-exclusion-undisturbed forest (SEUF), and snow undisturbed forest (SUF). The SEPF exhibited the significantly lowest mean R_s rates (0.71 μmol m^-2 s^-1) compared to the SPF (1.02 μmol m^-2 s^-1), SEUF (1.44 μmol m^-2 s^-1), and SUF (1.48 μmol m^-2 s^-1). The R_s also showed significant variations with time (p < .0001). However, treatments and time revealed no statistically significant interaction effects (p = .6801). Total winter R_s (January-March) ranged from 4.47 to 4.59 Mt CO₂ ha^-1 in the undisturbed forest and 2.20 to 3.16 Mt CO₂ ha^-2 in the postfire site. The R_s showed a significantly positive relationship (p < .0001) with the soil (0.59) and air (0.46) temperatures and a significantly negative relationship (p = .0017) with the soil moisture (-0.20) at the 5 cm depth. In contrast, the R_s indicated a negative but not statistically significant relationship (p = .0932) with the soil moisture (-0.16) at the 10 cm soil depth. The combined effects of lack of snow and forest fire significantly decreased R_s, thus conserving the soil's organic carbon stocks and reducing the CO₂ contribution to the atmosphere. In contrast, a warmer winter significantly increased R_s rates in the undisturbed forest, suggesting an acceleration of soil organic carbon losses and providing positive feedback to climate change.