Effects of fire history on thermal regimes of permafrost in the northern Da Xing’anling Mountains, NE China

Abstract

Forest fires potentially result in the irreversible and rapid degradation of permafrost, soil evolution, successions of boreal forests, and consequent development of hazardous periglacial landforms. Two burned-areas of Mangui and Alongshan at the western flank of the northern Da Xing’anling Mountains in Northeast China were chosen to study the effects of forest fires on thermal regimes of near-surface permafrost and the active layer. The study results show risen post-fire ground temperatures with increasing fire severity, and mainly at depths of 0–1.5 m. Moreover, nine years after a severe burn, the depth of evident temperature changes exceeded 6 m, and a warming of 2.7 °C at 6 m depth was inferred. Presumably due to the influences of forest fires, the active layer thickness at severely burned sites was 3.8 m compared to 1.2 m at the un-burned site. Soil moisture content and organic-layer and snow-cover thicknesses also play important roles in further complicating the fire impacts on the permafrost environment. These impacting mechanisms and thresholds await more systematic, in-depth, and quantitative studies. Numerical models deem necessary for simulating and predicting the spatiotemporal variations in ground hydrothermal regimes under different fire severity and for evaluating the contributions and thresholds of changes in these important environmental factors (e.g., organic layer and snow cover) for the hydrothermal state of near-surface permafrost and active layer.