森林过火区植被遥感参数的变化与恢复特征分析

遥感技术可以快速、准确地监测森林火灾火烧迹地的植被遥感参数变化,分析植被对火灾的响应与恢复特征,为防灾减灾决策提供科学依据。本文首先基于森林火灾前后的Landsat5 TM数据,利用差分归一化燃烧指数（the Differential Normalized Burn Ratio,dNBR）来提取2009年澳大利亚维多利亚州火烧迹地的范围,计算过火区面积及火烧强度;其次基于时间序列的全球地表特征参量（Global Land Surface Satellite,GLASS）产品中的叶面积指数（Leaf Area Index,LAI）、吸收光合有效辐射比例（Fraction of Absorbed Photosynthetically Active Radiation,FAPAR）数据,利用距平分析法对比不同火烧强度过火区植被与未过火区植被受森林火灾的影响状况与植被恢复特征。结果表明,森林火灾发生后,LAI、FAPAR值迅速降低,火烧强度越大,LAI、FAPAR下降程度越大,高火烧强度过火区的LAI、FAPAR最大降幅分别为中火烧强度、低火烧强度过火区的1.2、1.3倍;随时间推移,LAI、FAPAR值逐渐上升,在2-3年内恢复至未过火区水平。LAI、FAPAR恢复至未过火区平均水平的时间与森林火灾规模、火烧强度密切相关：维多利亚州森林火灾过火区域中大过火斑块、高火烧强度林地的植被遥感参数恢复时间相比小过火斑块、低火烧强度林地滞后1-2年。植被遥感参数LAI、FAPAR能很好地反映过火区植被的受损状况及恢复过程。

Analysis on the Characteristics of Change and Recovery of Vegetation Indices for Forests in Burned Area

The application of remote sensing technology to study the response and recovery of forest vegetation in burned area can provide scientific basis for quick and accurate disaster prevention and mitigation. We focus on the forest fire occurred in Victoria, Australia from February 7, 2009 to March 14, 2009, which was the most serious forest fire in Victoria. In order to analyze the characteristics of change and recovery of forest vegetation indices in response to forest fire, we first used Landsat5 TM data of pre-fire and post-fire to extract the burned area of Victoria in Australia in 2009 and calculate the burn severity based on the Differential Normalized Burn Ratio (dNBR). We analyzed the effects of forest fire with different burn severity on vegetation using the anomaly value of Leaf Area Index (LAI) and the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) of Global Land Surface Satellite product(GLASS). Based on the time series data of LAI and FAPAR, we analyzed the vegetation recovery characteristics affected by forest fire with different burn severity. The results showed that LAI, FAPAR can reflect the damage effects of forest fire on vegetation and tract the recovery process of vegetation well. The LAI and FAPAR values decreased rapidly after the forest fire. The greater the burn severity, the higher the decreasing amplitude. The maximum decreasing amplitude of LAI and FAPAR of high burn severity area were 1.2, 1.3 times higher than that of low burn severity area and medium burn severity area, respectively. The LAI and FAPAR values increased over a period of time after the forest fire and restored to normal levels in 2-3 years. The recovery time of LAI and FAPAR is related to fire scale, burn severity, the natural conditions of the burned area, the growth of the original vegetation and other factors. For example, one year after the forest fire in Victoria, the decreasing amplitude of LAI and FAPAR in small burned area was 4.8% of the big burned area. The recovery time of LAI and FAPAR in high burn severity area and big burned area was 1 year or 2 years later than that of low burn severity area and small burned area. This study analyzed the characteristics of the change of the vegetation indices (LAI and FAPAR) of vegetation affected by the forest fire and summarized the recovery characteristics of damaged vegetation in Victoria, which can provide scientific basis for formulation of the measures of forest fire recovery.