The charcoal content from laminated lake sediments in Québec, Canada, was estimated from pollen slides and by a sieving method. The resulting charcoal series are compared to estimate the suitability of these two methods to provide a local or regional fire history. The replication of five different charcoal series from the sieving method shows that this method is suitable for fire-history reconstruction. In our laminated sediments, 1cm³ is representative of the charcoal content of the sediment. The large charcoal fragments above 15600 mm²are too scarce, however, to provide a significant charcoal series. Comparison of the sieving charcoal series versus the pollen-slide charcoal-series shows that the two series display a roughly similar pattern. The differences between the two series probably result from the accumulation of small particles that have a regional source area and are transported by air over long distances and from high fragmentation rates due to laboratory treatment. Spectral analysis for the last 2000 years shows that the sieving charcoal series have no significant periodic accumulation rate, whereas the spectral analysis of the pollen-slide charcoal series shows a significant period of about 500 years. Because the charcoal particles from the sieving method are larger than those from the pollen-slide method, which are potentially windborne over long distances, our study suggests that the sieving method series is a proxy of local fire history, whereas the pollen-slide method is more suitable for detecting regional trends in fire history.

Climate, vegetation and humans act on biomass burning at different spatial and temporal scales. In this study, we used a dense network of sedimentary charcoal records from eastern Canada to reconstruct regional biomass burning history over the last 7000 years at the scale of four potential vegetation types: open coniferous forest/tundra, boreal coniferous forest, boreal mixedwood forest and temperate forest. The biomass burning trajectories were compared with regional climate trends reconstructed from general circulation models, tree biomass reconstructed from pollen series and human population densities. We found that non-uniform climate, vegetation and human drivers acted on regional biomass burning history. In the open coniferous forest/tundra and dense coniferous forest, the regional biomass burning was primarily shaped by gradual establishment of less climate-conducive burning conditions over 5000 years. In the mixed boreal forest an increasing relative proportion of flammable conifers in landscapes since 2000 BP contributed to maintaining biomass burning constant despite climatic conditions less favourable to fires. In the temperate forest, biomass burning was uncoupled with climatic conditions and the main driver was seemingly vegetation until European colonization, i.e. 300 BP. Tree biomass and thus fuel accumulation modulated fire activity, an indication that biomass burning is fuel-dependent and notably upon long-term co-dominance shifts between conifers and broadleaf trees.

A new global synthesis and biomization of long (> 40 kyr) pollen-data records is presented and used with simulations from the HadCM3 and FAMOUS climate models and the BIOME4 vegetation model to analyse the dynamics of the global terrestrial biosphere and carbon storage over the last glacial–interglacial cycle. Simulated biome distributions using BIOME4 driven by HadCM3 and FAMOUS at the global scale over time generally agree well with those inferred from pollen data. Global average areas of grassland and dry shrubland, desert, and tundra biomes show large-scale increases during the Last Glacial Maximum, between ca. 64 and 74 ka BP and cool substages of Marine Isotope Stage 5, at the expense of the tropical forest, warm-temperate forest, and temperate forest biomes. These changes are reflected in BIOME4 simulations of global net primary productivity, showing good agreement between the two models. Such changes are likely to affect terrestrial carbon storage, which in turn influences the stable carbon isotopic composition of seawater as terrestrial carbon is depleted in ¹³C.