Depth of Peat Burning and Carbon Loss during an Underground Forest Fire

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Among forest fires, underground (peat) fires lead in terms of the amount of material burned per unit area and, consequently, the impact on climate change, but they differ in the complexity of assessing the loss of soil carbon and its emissions to the atmosphere. Using the example of the 2010 forest and peat fire in Moscow oblast (an area of 9 ha with a variable original tree-stand composition), the depth of burnout and loss of soil carbon were determined by reconstructing the prefire soil surface along the root collar of stumps, as well as comparing the characteristics of peat on the burned and adjacent areas. The average (median) burnout depth was 15 ± 8 (14) cm, varying in different areas from 13 ± 5 (11) to 20 ± 9 (19) cm. The burnout depth increased with the relative surface height and was maximum in areas with a predominance of aspen. Based on the data of the layer-by-layer determination of the bulk density, ash content, and carbon content in peat, the dependences of the carbon stock on the peat thickness are obtained. Based on them, and according the depth of burning, the carbon losses are estimated, which amount to an average (median) of 9.8 ± 5.57 (9.22) kg m–2 for the burned-out areas, varying in different areas from 8.61 ± 3.75 (7.39) to 12.9 ± 6.18 (12.3) kg m–2, which is equivalent to a one-time emission of almost 400 t СО2 ha—1 and at least 1.5 times higher than the possible release of CO2 into the atmosphere from the loss of carbon biomass of a growing stand with a stem wood stock of more than 280 m3 ha–1. The results correspond to the upper limit of estimates of soil carbon losses obtained by foreign authors and confirm the underestimation of the factor of underground (peat) fires in the boreal zone in comparison with the tropics and in general when considering the influence of forest and peatland ecosystems on the gas composition of the atmosphere and climate.