火灾区域林地植被变化分析——以大兴安岭和黄石公园地区为例

Vegetation changes in conflagration area:Case study of Da Hinggan Mountains and Yellowstone National Park burned area

为了评估1987年大兴安岭和1988年黄石公园森林大火后植被的变化情况,以时间序列的Landsat地表反射率数据为基础,采用燃烧归一化指数(NBR)提取出火灾区域的范围,根据火灾前后归一化植被指数(NDVI)的差值对林地受灾情况进行分级以评价过火区林地受灾程度,根据不同年份NDVI的增长情况评价过火区林地的恢复情况.结果表明:①1987年大兴安岭火灾区域范围为6 695.53 km^2,重度烧毁区域的面积为4 738.55 km^2,受灾地区当年NDVI平均下降了66.32%;1988年黄石公园火灾区域范围为2 187.95 km^2,重度烧毁区域的面积为772.72 km^2,受灾地区当年NDVI平均下降了64.68%;②大兴安岭火灾区域灾后NDVI恢复速度较快,1988年NDVI恢复到1986年的65.65%,1999年NDVI值较1986年增长了12.90%;黄石公园火灾区域灾后NDVI恢复速度较为缓慢,1990年NDVI恢复到1988年的46.42%,1998年达到过火前NDVI的84.75%,直到2000年NDVI才恢复到火灾前的水平;人工促进更新辅助自然更新对火烧区林地植被恢复起到一定的促进作用.

In order to estimate the changes of vegetation in the burned area of the Da Hinggan Mountains after forest fire of1987 and the Yellowstone National Park after forest fire of 1988,normalized burn ratio(NBR)was used to extract the range of fire area,using the difference of normalization vegetation index(NDVI)before the fire and after the fire to classify the difference of the scale of the forest and the degree of forest disaster of fire area based on the time series data of Landsat albedos data.Then,using it to assess the recovery of forest in burned areas.The results showed that:①In 1987,the fire affected area reached 6 695.53 km^2,of which 4 738.55 km^2 were severely burned area.The NDVI dropped by 66.32%compared with the previous year in the burned area of the Da Hinggan Mountains;the fire affected area reached 2 187.95 km^2 in 1988,of which 772.72 km^2 were severely burned area.The NDVI dropped by 64.68%compared with the previous year in the burned area of the Yellowstone National Park.②NDVI recovered quickly after the fire in the Da Hinggan Mountains.NDVI recovered to 65.65%of that in 1986 in 1988.NDVI of 1999 increased by 12.90%compared with that of 1986.After the fire in the Yellowstone National Park,the recovery rate of NDVI was relatively slow,from 46.42%in 1990 to 84.75%in1998,the level of NDVI return to the vegetation coverage of the forest before the fire until 2000.Artificial regeneration plays an important role in forest vegetation restoration in burned area.