Climate change impacts are driving forest fires worldwide and reducing snowfall in temperate countries. Whether these impacts result in a significant alteration of winter soil respiration (Rs) rates and temperature in the postfire and the undisturbed black pine (Pinus nigra) forests remain poorly understood. A field experiment was conducted in the postfire and the undisturbed black pine forests during a winter period in Türkiye to quantify Rs rates as affected by lack of snow and snow cover. Four treatments were applied: snow-exclusion postfire (SEPF), snow postfire (SPF), snow-exclusion undisturbed forest (SEUF), and snow-undisturbed forest (SUF). The SEPF exhibited the significantly lowest mean Rs 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 Rs also showed significant variations with time (p <.0001). However, treatments and time exhibited no statistically significant interaction effects (p = 0.6801). Total amounts of winter Rs (January to March) ranged from 4.92 to 5.07 Mt CO2 ha-1 in the undisturbed forest and 2.53 to 3.51 Mt CO2 ha-2 in the postfire site. The Rs showed a significantly positive relationship (p <.0001) with the soil (0.59) and air (0.46) temperatures and a significantly negative relationship (p = 0.0017) with the soil moisture (-0.20) at the 5 cm depth. In contrast, the Rs showed a negative, but not statistically significant relationship (p = 0.0932) with the soil moisture (-0.16) at the 10 cm soil depth. The combined effects of lack of snow and forest fire resulted in a significant decrease of Rs. In contrast, a warmer winter significantly increased Rs rates in the undisturbed forest, suggesting that a warmer winter could potentially accelerate soil organic carbon losses in naturally growing undisturbed forest ecosystems, thus, providing positive feed backs to climate change.

Hydrological extremes and wildfires are increasing in magnitude and frequency due to climate change impacts; hence, it is essential to understand the compound effects of these disturbances on the different components of the global carbon cycle, particularly soil respiration (Rs). We conducted an experiment in a randomized complete block design with four replicate blocks to determine the compound effects of soil moisture extremes, types of forest fires, and aspects on Rs in postfire and undisturbed black pine (Pinus nigra Arnold) forest ecosystem. We measured Rs using an automated soil respiration machinery (LI-8100A, LiCor BioSciences), which also measures soil temperature, air temperature, and soil moisture simultaneously. The Rs exhibited significant differences among treatment combinations (p <.0001), time (p <.0001), and moisture regimes (p <0.0001) but not with the interaction effects of treatment x time (p = 0.0058), aspects (p = 0.95410), and types of forest fires (p = 0.0059). The compound effects of soil moisture drought x crown fire x exposed aspect revealed a significantly lowest Rs (1.21 µmol m-2 s-1) among treatment combinations. In contrast, the compound effects of water-saturated soil x types of forest x aspect showed no significant differences compared to the control. The Rs ranged from 1.21 to 1.81 µmol m-2 s-1 for the soil moisture drought x forest fires x aspects, 1.90 to 2.55 µmol m-2 s-1 for the water-saturated soil x forest fires x aspects, and 1.83 to 2.38 µmol m-2 s-1 for the control. The Rs exhibited a positive relationship with the soil temperature (r = 0.59) and the air temperature (r = 0.63) but negatively correlated with the soil moisture (r = -0.33). The soil and air temperatures showed a strongly positive correlation (r = 0.87), suggesting that a near-surface air temperature provides a good approximation of the soil temperature.