Theme: East-West Interdisciplinary Boreal Forest Fire Experiment, Part 3 Moderator: A. Granström and G. Ivanova 8.8.1995 16:30 Room: U16
Fire History of Bor Forest Island and Surrounding Pinus sylvestris Forests of the Dubches Plain, Siberia
Swetnam, Thomas W., Baisan, Christopher H., Ivanova, Gallina A.
We reconstructed the history of fires by sampling and dating fire-scarred trees. Fire years and approximate seasons of burning were determined by dendrochronologically dating the tree rings, and by studying the relative position of fire scars within the annual rings. Before the experimental burn of 1993 at least six fires burned portions of the island during the past six centuries (AD 1481, 1638, 1753, 1796, 1867, and 1956). Intervals between these fires ranged from 43 to 157 years, with a mean fire interval (MFI) of 95 years. Fire-scarred samples in pine forests adjacent to the island, but separated by wet bog, recorded nearly three times more fire dates during the same time period. Only two of the six fire dates on the island coincided with fire dates on the mainland (1753 and 1796). MFI in the mainland forest, and in two other pine forest sites on the Dubches Plain, ranged from about 25 to 40 years. Preliminary stand age structure estimates on Bor Forest Island, derived from increment cores taken from mature trees, suggests that the overstory is composed of at least two major cohorts establishing approximately 180, and 130 years ago. We speculate that these cohorts established following the fires of 1796 and 1867, respectively. Approximately 50 percent of the fire scars occurred within the earlywood portion of the tree rings, while the remainder occurred within the latewood, or on the boundary between two rings. This indicates that at least half of all past fires occurred during the cambial growing season, which probably extends from about June to July or August in this region.
Our findings suggest that relatively small stands of pine forest surrounded by bogs, such as Bor Forest Island, sustain lower fire frequencies because of they are isolated from fires spreading across the larger, more continuous fuels of surrounding forests. Differences in fire sources and frequency suggest that significant differences in forest age structure and species composition might also be expected in landscape patches of different sizes and isolation within the matrix of bogs and river drainages on the Dubches Plain.
Key words: fire history, dendrochronology, tree rings.
Correspondence: Thomas W. Swetnam, Laboratory of Tree-Ring Research, University of Arizona, USA-Tucson, AZ 85721