The macroscopic charcoal record in forested boreal peatlands in southeast Norway

Abstract

We present a spatial and quantitative analysis of the macroscopic charcoal record in 11 forested peat basins in a boreal forest landscape in southeast Norway. The areas of the basins ranged from 200 to 6400 m2 and our study is based on 247 peat sequences that were sampled from randomly selected positions. In total we found 1228 charcoal layers in these peat sequences, which altogether had a length of 551 m. The number of charcoal layers per sequence ranged from 0 to 31 and the average number of charcoal layers per sequence was 3.99±0.3 SE, giving a mean fire frequency of one per 475 years. The average charcoal layer contained 170 charcoal particles > 0.28 mm per 10 cm2, of which 30 were > 1 mm. Peat sequences that totally lacked macroscopic charcoal were found at all sites. Nonetheless, all sites have burned recurrently during the Holocene, since at least one sequence from each site had seven or more charcoal layers. Neither the number of layers nor particle size decreased with increasing distance to the surrounding forests, indicating an in situ charcoal production and deposition. The charcoal record was characterized by a striking spatial variability. Geostatistical analyses revealed a strong spatial structuring on fine scales, ie, c. 0.25-1.5 m, but there was no evidence for spatial structuring at between-site scales, demonstrating that the sites have idiosyncratic fire histories. The rate of charcoal deposition was greater for the period prior to establishment of Picea abies than for the post-establishment period.