大兴安岭北部森林大火导致多年冻土快速退化的水热机制

在气候变暖背景下，森林火灾不断增多。林火烧毁植被和有机层，改变下垫面性质，诱发多年冻土的快速退化及不可逆生态环境演替。多年冻土快速退化体现在浅表层地温快速升高、热融湖塘、热融滑塌、地表沉陷等热喀斯特现象发生和增强。林火造成冻土退化的原因已有一些分析，但冻土快速退化的水热过程机制研究亟待开展。大兴安岭地区位于北方森林和欧亚大陆多年冻土南缘，也是华北和东北地区重要的生态屏障和水源涵养区，其独特的兴安型多年冻土对气候变暖和林火十分敏感。因此，本项目选取大兴安岭北部林区为代表性研究区，拟通过野外调查、遥感反演、物探、室内试验和数值模型模拟相结合，定量研究不同火烧程度下活动层和浅层多年冻土水热变化特征和原因，以及北方森林植被和冻土景观的更新和演替。从而揭示林火导致的兴安型多年冻土快速退化的水热机制。本研究可为欧亚北方森林生态系统和兴安-贝加尔型多年冻土区生态环境的管护提供重要科学依据和数据支撑。

Under a warming climate, occurrences of forest fires have been increasingly more frequent and at larger scales and losses in northern ecosystems over the last few decades. Forest fire destroys vegetation and organic layer and changes the characteristics of terrestrial processes, which leads to a rapid degradation of the underlying permafrost and an irreversible succession of northern forest ecosystem. The rapid degradation of permafrost is reflected in the rapidly rising near-surface soil temperatures, the occurrences and enhancement of thermokarst phenomena such as thermokarst lakes and ponds, thaw slumping and surface subsidence. There have been some causal analyses on fire-induced gradual degradation of permafrost in northern forests, however, the mechanisms for hydrothermal impacts of forest fire on its induced rapid permafrost degradation, such as thermokarsting, landslides, sinkholes, retrogressive slumps, and enhanced hillslope thermal erosion, urgently needs systematic and in-depth research. The northern Da Xing’anling (Hinggan) Mountains in Northeast China is on the southern margin of the Eurasia permafrost zone and boreal forest belt, which serves as an important ecological preserve/barrier and water supply area for North and Northeast China. Its unique Xing’an permafrost is very sensitive to climate warming and environmental changes, such as forest fires. Therefore, representative sites in the northern Da Xing’anling Mountains are selected as the project research area, through the combination of field investigations, remote-sensing and geophysical inversions, numerical model simulations, the proposed program aims at quantitative research of the rapidly changing characteristics and influencing factors of soil temperature and moisture content in the active layer and near-surface permafrost under different fire severity and scales, successions of the northern forest ecosystem and permafrost landscapes. Thus, the program aims at revealing hydrothermal mechanisms of fire-induced rapid degradation of the Xing’an permafrost on the southeastern margin of the Eurasia boreal forests. This study will provide important scientific basis and data support for the management of northern ecological environment and the sustainable development of forestry in Xing’an-Baikal permafrost regions.