Red spruce forests persist without fire. Red spruce is easily killed by fire due to its thin bark, shallow roots, flammable needles, and lack of self-pruning [9,23,39]. Its slow early growth rate delays the formation of a corky layer, which increases the fire susceptibility of young trees . In a study based on a survey of foresters, Starker  rated the fire resistance of 22 New England tree species based on fire mortality and fire avoidance (occurrence in habitat that does not burn very often). Red spruce was not resistant in terms o fire mortality but moderately or very resistant in terms of fire avoidance, and was ranked 13th overall. Red spruce habitat is subject to few fires; fires that occurred in presettlement times were usually of low severity . Saunders  noted that old-timers claimed that forest fires would stop when they reached the spruce-fir forest boundary. Electrical storms are common in this area but are usually accompanied by sufficient rain, and fuels are usually moist . Severe surface fires probably occurred infrequently, during periods of prolonged drought, and usually affected forests that were breaking up due to wind, ice storm damage, or similar events that generate surface fuels [25,32,60,61,87]. The estimated natural fire return intervals for the northeastern United States and adjacent Canada range from 330 to 3,300 or more years [25,32,51,52,84]. Estimates of natural fire frequency have been complicated by human activities. Logging in these forests has resulted in an increase in fire frequency and intensity, particularly in logging slash [18,32,52]. The catastrophic fires of the 19th and 20th centuries can be attributed to human activities [21,32,52]. However, even with the increase in fires due to human activity, most fires are small and quickly suppressed. There should be sufficient time between fires for red spruce to regain dominance on most sites unless deliberately and/or repeatedly burned. It has been suggested that, in presettlement forests, the increase of dead fuels following spruce budworm outbreaks increased the likelihood of fire [21,25,32]. Such outbreaks are more common in balsam-fir-dominated forests than in red-spruce-dominated forests, but the two species usually occur together, in varying proportions. Before settlement by Europeans, forests in northern New England, the Adirondack Mountains, and the hillier sections of southern New England and Pennsylvania were not deliberately burned by Native Americans as were other areas in the northeastern United States .