Forest Floor Moisture Content and Fire Danger Indices in Alaska

This report summarizes activities from 2002 to 2004 undertaken by the U.S. Bureau of Land Management’s Alaska Fire Service and cooperating agencies to better understand the influence of forest floor moisture content on fire behavior in interior Alaska boreal spruce forest. Forest floor moisture measurements were derived by removing individual layers and oven-drying them. Forest fuel treatments (thinning and pruning) for fire hazard reduction were associated with drier moss and duff layers, indicating a fire behavior trade-off in those units designed to reduce forest fire hazard. Forest floor moisture contents were compared with indices of the Canadian Forest Fire Danger Rating System to “validate” the performance of the indices in Alaska for reflecting conditions in the moss and duff layers. In general, indices followed moisture trends, but during specific times during the season, disagreement was noted between indices and actual fuel moisture conditions. Results of experiments using automated electronic devices to estimate moss and duff moisture were encouraging and may provide a means to improve both start-up value determination for fire danger indices and rapid field assessment.