Burnt area mapping across Canada ' s boreal forest zone using SPOT VEGETATION calibrated with Landsat TM imageR ) fJ

Wildfires are a major source of disturbance to the boreal forest ecosystem as they have been documented to bum as much as 1.5 percent (22 million ha) of its global area in a single year (Cofer et a!., 1996). Fires in this ecosystem typically kill the standing trees and thus exert a dominant control on landscape level patterns of forest succession and stand age distribution (Johnson, 1992). Fire is an important factor modifying the carbon budget with in the boreal zone, which covers less than 17% of the Earth's surface area, yet accounts for more than 30% of its carbon storage (Kasischke, 2000). Carbon storage is directly modified by fire owing to the combustion of forest and ground layer biomass into atmospheric carbon (C02, CH4, CO). It is also indirectly modified due to shifts in stand age distribution and increased ground layer decomposition rates following fire (Kasischke, 2000). To assess these ecological and carbon budget impacts, a fundamental parameter that must be measured is the affected burnt area. This requires a method to map the spatial distribution of burnt forest over vast, remote areas in an accurate, consistent, and timely manner. Coarse resolution ("") km) satellite sensors, notably the AVHRR aboard the NOAA polar orbiters, have proven to be effective for detecting active boreal fires (Flannigan and Vonder Harr, 1986; Li et a!., 2000) and mapping the extent of burnt areas after fire (Cahoon et aI., 1994; Kasischke and French, 1995, Fraser et a!., 2000a). Such sensors are well suited to mapping boreal fires for several reasons: (I) they provide inexpensive, daily coverage of the global boreal zone; (2) more than 97% of the burnt area is caused by fire events> 10 km2, a size that is larger than sensor resolution; and (3) most burning involves crown fires that destroy the forest canopy, producing a large and immediate change in reflectance that can be easily identified. However, for satellite-based burnt area mapping at continental scales to be more robust, accurate, and widely adopted, two important issues need to be addressed. First, the remote sensing burnt area products