| Forest fire is an important disturbance factor in forest ecosystems,driving changes in soil structure and function,and profoundly affecting the physical and chemical properties,hydrological features,and erosion resistance of soil,which may lead to soil erosion,water and soil loss,and soil structural degradation.The impact of forest fire disturbance on soil is persistent over time.By studying the changes in soil hydrological characteristics and erosion resistance after forest fires in different years,slope directions,and soil depths,and extracting key indicators for comprehensive evaluation of soil erosion resistance in burned areas,scientific evidence can be provided for the systematic evaluation of the impact of forest fire disturbance on soil,which is of guiding significance for scientific fire prevention and post-fire restoration work.Therefore,in this study,the heavily burned areas and adjacent non-burned areas at different recovery years,slope directions,and soil depths were selected using the spatiotemporal match method as the research object in the Anning River Basin.The soil was investigated,sampled and analyzed to study the effects of forest fire disturbance on soil hydrological characteristics and erosion resistance,as well as the performance of various indicators at different slope directions and soil depths.The relationship between soil hydrological indicators and erosion resistance indicators in burned areas was explored by means of correlation analysis,principal component analysis,and membership function analysis,and the key indicators for evaluating soil erosion resistance in burned areas were extracted.A comprehensive evaluation of soil erosion resistance in burned areas in the Anning River Basin was conducted.The following main conclusions were drawn:（1）Forest fires had a significant impact on the hydro-physical properties of soil（P<0.05）,with a recovery period ranging from 5 to 13 years.Soil bulk density increased by11.7%due to forest fire disturbance,with a recovery period of 13 years.During the recovery period,soil bulk density initially decreased and then increased again.The increase in soil bulk density was greater on the sunny slope than on the shady slope,and the increase became greater as the soil depth increased.Soil moisture content,saturation moisture content,and porosity significantly decreased by 14%,9%,and 18%,respectively,due to forest fire disturbance,with recovery periods of 5,9,and 7 years,respectively.The decrease was greater on the shady slope than on the sunny slope,and the recovery period was longer for the sunny slope.The decrease in soil moisture content was more significant in shallower soil layers,with shorter recovery periods.Forest fires also caused a decrease in soil water-holding capacity.After a forest fire,the decline in soil moisture content corresponding to different soil water suction ranged from 9%to 15%,with a recovery period of 9 years.The decrease in soil water-holding capacity was less significant on the sunny slope than on the shady slope,but the recovery period was longer.The decrease in soil water-holding capacity was greater in shallower soil layers,with longer recovery periods.（2）Forest fires have altered the structure and stability of soil aggregates,as well as the organic matter content.Due to the disturbance caused by forest fires,the<0.25 mm micro-aggregates in the soil are transferred to larger aggregates,and the recovery period for each soil aggregate size ranges from 5 to 18 years.At the same time,forest fires have caused a decrease in mean weight diameter（MWD）,water-stable aggregates(WR0.25),aggregate stability index（ASI）,and geometric mean diameter（GMD）of soil aggregates,leading to an increase in the percentage of aggregate destruction（PAD）and organic matter content（SOM）.The recovery period for WR0.25,MWD,GMD,and ASI is 13 years,while that for PAD and SOM is 7 and 22 years,respectively.The impact of forest fires on soil anti-erosion properties is more significant and has a longer recovery period on the sunny slope than on the shady slope.The recovery period for WR0.25,MWD,GMD,and ASI on the sunny slope is up to 13 years,while the recovery period for PAD and SOM is 7 and18 years,respectively.In contrast,the recovery time for the corresponding indicators on the shady slope is 9 years,5 years,and 26 years,respectively.At different soil depths,the changes in various soil anti-erosion indicators show that the shallower the soil layer,the greater the variation and the longer the recovery period.The recovery periods for different anti-erosion indicators in the 0-10 cm,10-20 cm,and 20-30 cm soil layers are 26 years,18 years,and 13 years,respectively.（3）Using principal component analysis and soil anti-erodibility index（SAI）to comprehensively evaluate the soil anti-erosion of burned areas,it is demonstrated that forest fires significantly weaken soil anti-erosion properties,with impacts lasting up to18 years.Post-fire,SAI decreased by 44%and exhibited a slow-to-fast recovery rate,eventually stabilizing at 1.22 after 18 years,approaching control levels.The reduction in soil anti-erosion on south-facing slopes outstripped that of north-facing slopes,decreasing by 50.4%and 46.7%,respectively.Recovery rates were faster during the first seven years,gradually slowing down thereafter,with recovery times of 18 and 13 years for south-facing and north-facing slopes,respectively.Forest fires led to reduced soil anti-erosion at different depths,particularly within the 0-10 cm layer,where SAI decreased by 50.2%.As the depth of soil increased,the recovery period for soil anti-erosion shortened;in the0-10 cm,10-20 cm,and 20-30 cm layers,the recovery periods to control levels were 22,18,and 13 years,respectively.Soil anti-erosion was observed to decrease with increasing soil depth.（4）Results obtained from the soil anti-erosion index model are consistent with those derived from principal component analysis.Thus,based on the four optimized indicators established via principal component analysis,soil anti-erosion can be comprehensively evaluated,which include aggregate destruction rate,aggregate stability index,>0.25 mm water-stable aggregate content,and saturation moisture content.This study focused on heavily burned areas with different recovery periods to explore the impact of forest fires on soil hydrological characteristics and anti-erosion properties.The spatiotemporal method was used to investigate the dynamic changes in soil hydrological characteristics and anti-erosion properties after severe forest fires,and to analyze their performance on different slopes and soil depths.Furthermore,key indicators for comprehensively evaluating the soil anti-erosion properties of burned areas were optimized.This provides a scientific basis for the systematic evaluation of the impact of forest fires on soil,and has guided implications for scientific fire prevention and post-fire restoration work. |
