Fire frequency and forest structure at a dry site between AD 440 and 1110 based on charcoal and pollen records from a laminated lake sediment in eastern Finland

Abstract

The fire history of a dry Boreal forest site in eastern Finland before settlement in the area was studied by means of charcoal and pollen analysis of annually laminated lake sediments. The average estimated local fire interval of 70-80 years corresponds to values quoted in a few earlier Finnish studies based on annually laminated lake sediments from more mesic sites. The fire interval is longer than expected from dendrochronological results obtained for dry sites in Fennoscandian forests, suggesting human influence during the periods studied by the dendrochronological method. The high representation of Picea pollen preceding the period of slash-and-burn cultivation at this and some other dry sites suggests a mixed coniferous forest structure at dry forest sites before significant human influence. The charcoal influx reflected estimated climatic shifts, suggesting that the fires increased during the warmer climatic periods. A small test comparing charcoal records on pollen slides with thin sections was included in this study. Large macroscopic charcoal particles were so scarce in the sediment of Lake Laukunlampi that two local fires discernible in the pollen and microscopic charcoal records could not be detected in the thin sections.