| Disturbances are mechanisms that mediate ecosystem changes in response to climate-driven vegetation changes. While many studies have looked at the effect of fire on ecosystem components, few have considered the response of fire to climate and vegetation change. The effects that past climate and vegetation shifts have on fire regimes and the potential consequences to ecosystem change are examined here.; Charcoal and pollen analyses were used to determine geographic and temporal patterns of past fire regimes in the North American western boreal forest. Seventeen high-resolution records from north-central Canada (NWT and Manitoba), interior Alaska, and northwestern Ontario were analyzed for large charcoal particles in continuously sampled sediment cores to calculate fire return intervals during the Holocene. Fire, vegetation, and climate data were used to interpret regional and temporal differences in fire importance. In addition, sediment charcoal accumulation was compared to modern experimental fires to interpret fire events from sediment records.; Particle-size distributions were equal among all lakes, and deposition occurred directly from fires, not from secondary deposition following fires. Based on the similar patterns of charcoal accumulation from the modern burn and particle-size distributions, the largest 10% of charcoal accumulation rates represent individual fire events. The Holocene records show variations among the regions in timing of the maximum fire period (highest charcoal accumulation rates and shortest fire return intervals). The maximum fire period occurred prior to 5,000 yr BP (calendar years before 1950) for North-central Canada in response to a dry climate regime. In interior Alaska, fire was unimportant until the establishment of Picea mariana at 5,500 yr BP. In northwestern Ontario, the maximum fire period occurred between 2,200 yr BP and present in response to climate-induced forest structure shifts. Despite the different timings, the mean fire return intervals of 70--100 years are characteristic of each maximum fire period. Modern fire regimes for these regions developed at approximately 2000 yr BP with fire-return intervals ranging from 70 years in the mixed boreal forest to 600 years in the northern lichened boreal woodlands. Twentieth century charcoal accumulation increases suggest that modern fire regimes may have been influenced by recent climate changes. |
