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

•Forest fire has evident influences on hydrothermal regimes of permafrost.•Fire-induced hydrothermal changes tend to enlarge with increasing fire severity.•Changes in hydrothermal regimes are evident in near-surface permafrost after fires.•The freeze–thaw processes after fire differ evidently from those of unburned sites.