Changes in surface albedo after fire in boreal forest ecosystems of interior Alaska assessed using MODIS satellite observations

We assessed the multidecadal effects of boreal forest fire on surface albedo using Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations within the perimeters of burn scars in interior Alaska. Fire caused albedo to increase during periods with and without snow cover. Albedo during early spring had a mean of 0.50 +/- 0.03 for the first three decades after fire, substantially higher than that observed in evergreen conifer forests (0.34 +/- 0.04). In older stands between 30 and 55 years, albedo showed a decreasing trend during early spring, probably from a growing spruce understory that masked surface snow and caused increases in both simple ratio (SR) and enhanced vegetation index (EVI). During summer, albedo decreased by 0.012 +/- 0.005 in the year immediately after fire (from 0.112 +/- 0.005 to 0.100 +/- 0.010). In subsequent years, summer albedo increased rapidly at first and then more gradually, reaching a broad maximum in 20 - 35 year stands (0.135 +/- 0.006). These measurements provide evidence for a well-developed deciduous shrub and tree phase during intermediate stages of succession. Averaged over the first 5 decades, shortwave surface forcing from fires was -6.2 W m(-2) relative to an evergreen conifer control and -3.0 W m(-2) relative to a control constructed from 2000 to 2003 preburn observations. These forcing estimates had a magnitude substantially smaller than previous estimates and suggest that, at a regional scale, evergreen conifer stand density may be lower than that inferred from chronosequence studies.