A 1300-year forest-fire history at a site in eastern Finland based on charcoal and pollen records in laminated lake sediment

Abstract

The charcoal and pollen stratigraphy of an annually laminated sediment of a small lake in eastern Finland (63°109N, 30°589E) was examined, and found to cover a period of 1300 years. The region around the lake is remote and nowadays almost unpopulated. The fire interval around the study lake was 85 years, with a range of 60–134 years during the 900-year period before any major human influence, and the corresponding fire rotation time estimate was c. 130 years. About half of the fires were probably mild surficial fires, leaving most Scots pine alive. Only one extensive, catastrophic fire during the 900-year period was evident. The fires maintained the forest succession cycles before human influence. The abundance of smallest charcoal particles and trends in estimated palaeotemperatures showed congruence, suggesting increased burning in large regions during warmer climatic periods. The charcoal influx values increased markedly from c. ad 1600 onwards due to the commencement of slash-and-burn cultivation in the area. The pollen and charcoal evidence suggests a period of extensive slash-and-burn agriculture from c. ad 1720 to the beginning of the twentieth century. The short fire interval during the slash-and-burning period caused major changes in forest structure: spruce decreased considerably, and pine became the dominant tree in the area. The charcoal influx into the lake has increased since the beginning of the present century despite fire suppression and the charcoal particle-size distribution suggests long distance origin for these particles.