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.

Paleofire events obtained from the statistical treatment of sedimentary charcoal records rely on a number of assumptions and user's choices, increasing the uncertainty of reconstructio\ns. Among the assumptions made when analyzing charcoal series is the choice of a filtering method for raw Charcoal Accumulation Rate (CHAR_raw). As there is no ultimate CHAR_raw filtering method, we propose an ensemble‐member approach to reconstruct fire events. We modified the commonly used procedure by including a routine replicating the analysis of a charcoal record using custom smoothing parameters. Dates of robust fire events, uncertainties in fire‐return intervals and fire frequencies are derived from members' distributions. An application of the method is used to quantify uncertainties due to data treatment in two CHAR_raw sequences from two different biomes, subalpine and boreal.

Assessment of biodiversity in a changing world is a key issue and studies on the processes and factors influencing its history at relevant time scales are needed. In this study, we analysed temporal trends of plant diversity using fossil pollen records from the North American boreal forest-taiga biome (NABT). We selected 205 pollen records spanning the last 15,500 years. Diversity was decomposed into α and γ richness, and β diversity, using Shannon entropy indices. We investigated temporal and spatial patterns of β diversity by decomposing it into independent turnover (variation in taxonomic composition due to species replacements) and nestedness (variation due to species loss) components. The palynological diversity of the NABT biome experienced major rearrangements during the Lateglacial and early Holocene in response to major climatic shifts. The β nestedness likely reflected plant immigration processes and generally peaked before the β turnover value, which mirrors spatial and temporal community sorting related to environmental conditions and specific habitat constraints. Palynological diversity was generally maximal during the Lateglacial and the early Holocene and decreased progressively during the Holocene. These results are discussed according to macro-ecological processes, such as immigration, disturbances and environmental fluctuations, with climate most notably as the main ecological driver at millennial scales.

We developed an algorithm to improve richness assessment based on paleoecological series, considering sample features such as their temporal resolutions or their volumes. Our new method can be applied to both high- and low-count size proxies, i.e. pollen and plant macroremain records, respectively. While pollen generally abounds in sediments, plant macroremains are generally rare, thus leading to difficulties to compute paleo-biodiversity indices. Our approach uses resampled macroremain influxes that enable the computation of the rarefaction index for the low influx records. The raw counts are resampled to a constant resolution and sample volume by interpolating initial sample ages at a constant time interval using the age∼depth model. Then, the contribution of initial counts and volume to each interpolated sample is determined by calculating a proportion matrix that is in turn used to obtain regularly spaced time series of pollen and macroremain influx. We applied this algorithm to sedimentary data from a subalpine lake situated in the European Alps. The reconstructed total floristic richness at the study site increased gradually when both pollen and macroremain records indicated a decrease in relative abundances of shrubs and an increase in trees from 11,000 to 7,000 cal BP. This points to an ecosystem change that favored trees against shrubs, whereas herb abundance remained stable. Since 6,000 cal BP, local richness decreased based on plant macroremains, while pollen-based richness was stable. The reconstructed richness and evenness are interrelated confirming the difficulty to distinguish these two aspects for the studies in paleo-biodiversity. The present study shows that low-influx bio-proxy records (here macroremains) can be used to reconstruct stand diversity and address ecological issues. These developments on macroremain and pollen records may contribute to bridge the gap between paleoecology and biodiversity studies.

This report summarizes the outcome of the PAGES Global Paleofire Working Group workshop 2017 that took place in Montreal, Canada-Paleofire knowledge for current and future ecosystem management. The workshop aimed to (1) discuss the importance of past fire or paleofire research, focused on long-term influence of fire on the environments worldwide, in nature conservation, (2) find ways to integrate scientific achievements of paleofire research into ecosystem management practices, and (3) start the dialogue with ecosystem managers, practitioners and policymakers (EMPPs). With this report, the members of the Global Paleofire Working Group would like to open a discussion about how igniting new collaborations with EMPPs and make paleofire data useful for fire risk management. We recognized four main challenges in communication and cooperation between scientists and EMPPs: little awareness of EMPPs about paleofire research, differences in professional language used in an operational context by scientists and EMPPs, scientific data availability, and costs of paleoecological expertise. Moreover, we indicate the way to improve the communication between scientists and EMPPs by proposing a scheme of cooperation between both groups. We want to encourage researchers working in various fields of paleoecology to open up for the cooperation with EMPPs in the future, especially helping to create ecosystem management plans, because paleoecological data carry important information about the evolution of ecosystems that is vital in the context of global change.