Interpretation of charcoal morphotypes in sediments from Ferry Lake, Wisconsin, USA: do different plant fuel sources produce distinctive charcoal morphotypes?

We describe five common charcoal morphotypes observed in late-Holocene lake sediments from northern Wisconsin and compare them with charcoal produced by burning modern plant material. Our experiments show that grass cuticle, conifer wood and leaves of some broadleaved taxa all produce recognizable charcoal types that are preserved in sediments. We use the identification of charcoal morphotypes to enhance our interpretation of a previously published charcoal record from Ferry Lake, Wisconsin. The occurrence of the different charcoal morphotypes changed as the vegetation and fire regimes changed over the past 2300 yr. Charred grass cuticle was more common before 1300 cal. yr BP when small charcoal peaks were frequent and the pollen assemblage suggests that an open oak savanna surrounded the lake. Charcoal with bordered pits produced from burned conifer wood was more common after 1300 cal. yr BP, when red/jack pine pollen increased and the frequency of charcoal peaks decreased, suggesting a switch from a surface fire regime to one with less frequent crown fires. Our results suggest that stratigraphic changes in the occurrence of charcoal morphotypes can improve our understanding of past vegetation and fire regimes.