基于Landsat时间序列数据的火烧迹地识别与恢复效果评价

Evaluation of Recognition and Restoration Effect of Burned Areas Based on Landsat Time Series Data

为研究大兴安岭地区火烧迹地识别和火后植被恢复状况,基于2006—2020年Landsat TM遥感影像,利用Google Earth Engine编写代码,以2006年大兴安岭地区松岭区那源林场森林火灾为研究背景,以差分归一化燃烧指数(dNBR)为基础数据进行火烧迹地识别,并对火烧烈度进行轻度、中度、重度和极重的等级划分;基于火烧迹地的增强型植被指数(EVI)值,采用一元线性回归分析、用于气候诊断与预测的Mann-Kendall突变检验法和用于做趋势分析的Theil-Sen median趋势分析等方法分析火烧迹地2006—2020年的植被恢复特征,探究大兴安岭地区火烧迹地植被恢复进程。结果表明,1)基于dNBR得到研究区过火面积为2488.7 hm^(2),其中轻度、中度、重度和极重火烧迹地面积占比分别为23.5%、9.6%、35.2%和31.7%,重度和极重过火区分布于火烧迹地西部和东部,过火强度从中部向南部和北部逐渐降低,其EVI值与火烧前相比分别下降了约30%、40%、58%和67%;2)不同烈度林地火烧迹地EVI恢复速率由大到小表现为极重、重度、中度、轻度,植被恢复过程中,迹地EVI值逐渐增加,其中,轻度和中度火烧迹地可在火后6~8 a恢复,而重度火烧迹地的恢复则需14 a;3)火烧迹地恢复过程中,林地EVI突变点较灌草地少,说明森林生态系统较灌草地稳定性强。不同烈度林地火烧迹地的突变情况也存在一定差异,且对照区的突变时间点滞后于火烧迹地。

To study the identification of burned areas and post fire vegetation restoration in the Daxing′an Mountains region,based on Landsat TM remote sensing images from 2006 to 2020,Google Earth Engine was used to write code.The research background was the 2006 forest fire in the Nayuan Forest Farm in the Songling District of the Daxing′an Mountains region.The differential normalized burned ratio(dNBR)data was used to identify the burned areas,and the severity was classified into mild,moderate,severe,and extremely severe levels.Based on the Enhanced Vegetation Index(EVI)values of burned areas,methods such as univariate linear regression analysis,Mann-Kendall mutation test for climate diagnosis and Theil-Sen media trend analysis for treud analysis were used to analyze the vegetation restoration characteristics of burned areas from 2006 to 2020,and to explore the process of vegetation restoration in the Daxing′an Mountains region.The results showed that,1)Based on dNBR,the burned areas in the study area was 2488.7 hm^(2),with 23.5%,9.6%,35.2%,and 31.7%of the areas affected by mild,moderate,severe,and extremely severe fires,respectively.Severe and extremely severe areas of excessive fire were distributed in the western and eastern parts of the burned area,and the severity of excessive fire gradually decreased from the central to the southern and northern parts.The EVI values decreased by about 30%,40%,58%,and 67%compared to before the fire,respectively.2)The recovery rate of EVI in forest burned areas with different intensities showed extremely severe,severe,moderate,mild.During the vegetation restoration process,the EVI value of the burned areas gradually increased.Mild and moderate burned areas can recover 6-8 years after the fire,while the recovery of severely burned areas required 14 years.3)During the restoration process of burned areas,there were fewer EVI mutation points in forested areas compared to grasslands,indicating stronger stability of forest ecosystems compared to irrigated grasslands.There were also certain differences in the mutation situation of forest burning sites with different intensities,and the mutation time point in the control area lagged behind the burning sites.