The Impact Of Forest Fire Disturbance On Permafrost And Vegetation In The Northern Great Xing’an Mountains Of Inner Mongolia

Habitat and vegetation changes in ecotone areas under the background of climate change have been a hot topic in the global ecological field in recent years.However,previous studies have mostly focused on macroscopic or microscopic perspectives to investigate the response and adaptation of vegetation to climate change,with limited exploration of the impact of natural disasters and habitat changes on vegetation at the regional scale.Taking the northern part of the Daxing’an Mountains,Inner Mongolia,as our study region,based on remote sensing,unmanned aerial vehicles(UAVs),and field measurements data,combined cloud processing and local analyzing,used Statistical Analysis,Landtrendr model and Geodector,investigated the dynamic changes of permafrost degradation(habitat change)and vegetation in response to forest fire disturbances(natural disasters).The study analyzed the effects of forest fire disturbances on permafrost and vegetation at different spatial and temporal scales,providing important scientific insights into understanding and predicting the future changes in forests in the Daxing’an Mountains.It also offered important theoretical foundations for forest fire prevention and ecological construction.The main conclusions of this study are as follows:(1)Regional forest fires are mainly caused by lightning strikes,accounting for97.99% of all forest fires,and they mainly occur from June to July,showing an increasing trend over the years.Spatially,forest fires exhibit a northward increasing trend from south to north.Lightning activity is a factor influencing the frequency of lightning fires,while climatic conditions such as water deficit,slope direction,maximum surface temperature,wind direction,and surface air pressure are the dominant factors affecting the burned area.(2)The regional permafrost shows a degradation trend from southeast to north.The zonality of regional permafrost differentiation is ranked as latitude(R~2=0.32)> altitude(R~2=-0.23)> longitude(R~2=0.17).Fire disturbances accelerate permafrost degradation,manifested by an increase in the surface temperature of the permafrost and the thickness of the active layer,as well as a decrease in the depth of permafrost freezing,with an increase in burned area or fire disturbance frequency.Significant permafrost degradation is observed in the burned areas,with the surface temperature of the permafrost increasing by approximately 0.05 ℃ and the thickness of the active layer decreasing by approximately 0.18-0.32 m during the 17 years after the fire.The depth of permafrost freezing also decreased by approximately 0.2-0.28 m.(3)Burned areas have lower annual vegetation coverage and a lower annual growth rate compared to the overall regional vegetation,with a decrease of approximately 1.3-2%.The hydrothermal changes caused by permafrost degradation advance the onset of greening,while the surface water changes resulting from permafrost degradation may delay the peak growing season and senescence.A certain degree of lightning fires has a promoting effect on regional vegetation growth,but when the burned area ≥10 hm~2 or the frequency of lightning fires ≥50 events/km~2,the accelerated permafrost degradation caused by lightning fire disturbances will have irreversible impacts on vegetation.Vegetation recovery in burned areas can be divided into three stages: rapid recovery in the short term(2-5 years)after forest fires,sustained recovery in the medium term(5-10years),and slow recovery of vegetation in the long term.The long-term effects of post-fire permafrost degradation will have a lasting impact on vegetation growth in burned areas.In the short term,vegetation recovery is mainly limited by evapotranspiration and soil moisture,while in the long term,climate,especially the hydrothermal cycle,is the main influencing factor for vegetation recovery.The vegetation recovery rate can reflect the surface growth changes of vegetation(R~2>0.3,P<0.05).Vegetation with higher recovery rates has better growth within the recovery trajectory,and the proportion of shrubs,such as Rhododendron dauricum,is larger.In conclusion,under the background of climate change,the intensification of forest fire disturbances and the continued permafrost degradation in the northern part of the Daxing’an Mountains in Inner Mongolia will have long-term effects on regional vegetation growth.The accelerating effect of fire disturbances on permafrost degradation will have long-term impacts on vegetation growth in the region.The hydrothermal changes resulting from short-term permafrost degradation after fires promote the increase of fast-growing vegetation in the region,while long-term habitat changes may lead to certain changes in the species composition of regional vegetation.