Mid to late Holocene fire and climate dynamics inferred from lake sediments from interior British Columbia, Canada

A number of distinct charcoal morphotypes were defined in this study and used along with diatom assemblages from lake sediments to investigate the relationships between fire and climate at decadal through millenial scales from the Interior British Columbia. Charcoal fragments were classified into seven distinct morphotypes according to their morphological and structural characteristics using optical microscopy. The contemporaneous relationship between charcoal morphotypes and recorded area burned was assessed from three lakes in different biogeoclimatic zones, between 1919-2000. The distribution of each charcoal morphotype showed distinct differences over time. In Prosser Lake type-M charcoal was significantly correlated to area burned around Prosser Lake at radii up to 20 km, whereas type-C morphotype was correlated to area burned at a radius <10 km, and type S at a 20-km radius. In Opatcho Lake, morphotype M was the only charcoal type significantly correlated with area burned. Charcoal from Big Lake was inversely related to past area burned, suggesting important contribution from secondary deposition. The strong correlation between type-M charcoal and area burned was used to develop an index of area burned.; The charcoal-morphotype approach at inferring past fires was further assessed by longer-term reconstructions of climate at a sub-decadal resolution over the past 400 years and centennial-scale resolution over the last six millennia in sediment cores from Opatcho Lake. Climate proxies were developed using variations in diatom assemblages and supported with regional proxies of temperature and precipitation. In both cases, the reconstructions indicates that synoptic-scale climate variations were significantly related to morphotype-based reconstruction of fire, but were not related to total charcoal.; This new technique suggests that fires were ∼5 times more common than present day between 4500-6000 yrs B.P., a well known period of aridity. Models suggest that B.C. will get increasingly arid. A similar fire regime to that observed in the mid Holocene should be expected.