Forest fire scar detection in the boreal forest with multitemporal SPOT-VEGETATION data

—Disturbance events, such as fire, have a major impact on boreal forest dynamics, succession and the global carbon cycle. Methods using satellite imagery are well established for detecting forest fires in real time and mapping the burned area (fire scars) within one year of the fire. This paper focuses on the detection of older fire disturbance-regeneration patterns in the boreal forests of Canada. Previous work found that shortwave-infrared image segmentation proved particularly good at creating uniform regions that were easy to associate with fire scars. Our findings suggest it is possible to detect fire scars up to 10 years old using SPOT VEGETATION data from a single year and that the use of a vegetation index based on near-and shortwave-infrared reflectance is critical to this success. We demonstrate how the use of short term multi-temporal imagery can enhance segmentation results and present a threshold-based procedure for a-posteriori identification of fire scar segments. The resulting fire scar probability map showed a good correspondence with records of fire scars mapped by the Canadian Forest Service for 1980-1992 and 'hot spots' from the FireM3 Information System for 1994-1998. Boreal forests play an important role in the global carbon budget. The boreal forest contains approximately 49% of the total carbon pool in forested ecosystems [1]; it extends throughout the Northern circumpolar region and covers approximately 10% of the Earth's land surface. The effects of fire disturbance on this ecosystem are potentially catastrophic, because it is very slow growing, with a short active period, typically 120-150 days [2] and subject to nutrient limitation. Further, while the biome contains a high carbon mass, most of this is stored in soil and replacement is limited by temperature and nutrient controls on decomposition [1]. Because forest fires typically release high levels of energy, soil is likely to be combusted.Goulden et al. [3] showed that the carbon losses are not recovered by regrowth, at least in northern boreal forests, where net sequestration into woody biomass is balanced by the release of ancient soil carbon as a direct result of the lowering of the permafrost layer. There are large annual fluctuations in the area affected by fire; in typical years 5-10 million ha may be burnt [4]; [5]. Examination of decadal averages has shown that 95% of the area burned is caused by 3% of fires [6]. Fires also occur in temporal clumps rather than having a consistent average. These …