Forecasting model of Corylus, Alnus, and Betula pollen concentration levels using spatiotemporal correlation properties of pollen count

The aim of the study was to create and evaluate models for predicting high levels of daily pollen concentration of Corylus, Alnus, and Betula using a spatiotemporal correlation of pollen count. For each taxon, a high pollen count level was established according to the first allergy symptoms during exposure. The dataset was divided into a training set and a test set, using a stratified random split. For each taxon and city, the model was built using a random forest method. Corylus models performed poorly. However, the study revealed the possibility of predicting with substantial accuracy the occurrence of days with high pollen concentrations of Alnus and Betula using past pollen count data from monitoring sites. These results can be used for building (1) simpler models, which require data only from aerobiological monitoring sites, and (2) combined meteorological and aerobiological models for predicting high levels of pollen concentration

Holocene fire activity during low-natural flammability periods reveals scale-dependent cultural human-fire relationships in Europe

Fire is a natural component of global biogeochemical cycles and closely related to changes in human land use. Whereas climate-fuel relationships seem to drive both global and subcontinental fire regimes, human-induced fires are prominent mainly on a local scale. Furthermore, the basic assumption that relates humans and fire regimes in terms of population densities, suggesting that few human-induced fires should occur in periods and areas of low population density, is currently debated. Here, we analyze human-fire relationships throughout the Holocene and discuss how and to what extent human driven fires affected the landscape transformation in the Central European Lowlands (CEL). We present sedimentary charcoal composites on three spatial scales and compare them with climate model output and land cover reconstructions from pollen records. Our findings indicate that widespread natural fires only occurred during the early Holocene. Natural conditions (climate and vegetation) limited the extent of wildfires beginning 8500 cal. BP, and diverging subregional charcoal composites suggest that Mesolithic hunter-gatherers maintained a culturally diverse use of fire. Divergence in regional charcoal composites marks the spread of sedentary cultures in the western and eastern CEL The intensification of human land use during the last millennium drove an increase in fire activity to early-Holocene levels across the CEL Hence, humans have significantly affected natural fire regimes beyond the local scale - even in periods of low population densities - depending on diverse cultural land-use strategies. We find that humans have strongly affected land-cover- and biogeochemical cycles since Mesolithic times

The Eurasian Modern Pollen Database (EMPD), version 2

The Eurasian (née European) Modern Pollen Database (EMPD) was established in 2013 to provide a public database of high-quality modern pollen surface samples to help support studies of past climate, land cover, and land use using fossil pollen. The EMPD is part of, and complementary to, the European Pollen Database (EPD) which contains data on fossil pollen found in Late Quaternary sedimentary archives throughout the Eurasian region. The EPD is in turn part of the rapidly growing Neotoma database, which is now the primary home for global palaeoecological data. This paper describes version 2 of the EMPD in which the number of samples held in the database has been increased by 60 % from 4826 to 8134. Much of the improvement in data coverage has come from northern Asia, and the database has consequently been renamed the Eurasian Modern Pollen Database to reflect this geographical enlargement. The EMPD can be viewed online using a dedicated map-based viewer at https://empd2.github.io and downloaded in a variety of file formats at https://doi.pangaea.de/10.1594/PANGAEA.909130 (Chevalier et al., 2019)Swiss National Science Foundation | Ref. 200021_16959

Analisis of pollen profiles from the region of barrowfield complex at Uniradze-Przewóz, Kaszuby Lake District (N. Poland)

Agnieszka Uziębł

Holocene fires in the central European lowlands and the role of humans

International audienceA major debate concerns the questions of when and to what extent humans affected regional landscapes, especially land cover and associated geomorphological dynamics, significantly beyond natural variability. Fire is both, a natural component of many climate zones and ecosystems around the globe and also closely related to human land cover change. Humans clearly affected natural fire regimes and landscapes in the most recent centuries, acting as prime ignition triggers and later fire suppressors, while Holocene trends in sedimentary charcoal have been mainly associated with climatic factors and partly with Neolithic land cover change. However, little is known since when Paleolithic to Neolithic fire use affected natural landscapes beyond small spatial and temporal scales. Here, we discuss onset and extent of human-driven fires superimposed on natural Holocene landscape transformation for the central European lowlands (CEL), a landscape of low natural flammability and long human history. We present composites of sedimentary charcoal records as new human impact proxies for periods when natural conditions (climate and vegetation) limited wildfires. Together with climate model output and land cover reconstructions from pollen, we find that fire was naturally important only during the early Holocene. The onset of human-driven fires beyond natural fires appeared scale-dependent. Sub-regional fire maxima indicate fire use by Mesolithic hunter-gatherers, already 8,500 years ago. Regionally, fire marks the Neolithisation onset at ∼6,500 years (western CEL) and ∼4,000 years ago (eastern CEL). During the last millennium, farming intensification drove fire up to early Holocene levels across all CEL. Fire activity reduced only in the highly fragmented landscape of northern Germany during the last centuries. As compilations of soil erosion records even mirror Holocene fire trends, we conclude that past human land cover change could have affected sub-regional landscapes more and earlier than previously thought

Forecasting model of Corylus, Alnus, and Betula pollen concentration levels using spatiotemporal correlation properties of pollen count

The aim of the study was to create and evaluate models for predicting high levels of daily pollen concentration of Corylus, Alnus, and Betula using a spatiotemporal correlation of pollen count. For each taxon, a high pollen count level was established according to the first allergy symptoms during exposure. The dataset was divided into a training set and a test set, using a stratified random split. For each taxon and city, the model was built using a random forest method. Corylus models performed poorly. However, the study revealed the possibility of predicting with substantial accuracy the occurrence of days with high pollen concentrations of Alnus and Betula using past pollen count data from monitoring sites. These results can be used for building (1) simpler models, which require data only from aerobiological monitoring sites, and (2) combined meteorological and aerobiological models for predicting high levels of pollen concentration

Fire risk modulation by long-term dynamics in land cover and dominant forest type in Eastern and Central Europe

International audienceWildfire occurrence is influenced by climate, vegetation and human activities. A key challenge forunderstanding fire-climate-vegetation interactions is to quantify the effect vegetation has in mediating fire regime. Here, we explore the relative importance of Holocene land cover and dominant functional forest type, and climate dynamics on biomass burned in temperate and boreo-nemoral regions of Central and Eastern Europe over the past 12 ka BP years. We used an extensive data set of Holocene pollen and sedimentary charcoal records, in combination with climate simulations and novel statistical modelling. Biomass burned was highest during the early Holocene and lowest during the mid Holocene in all three ecoregions, but diverged more markedly over the past 3-4 ka BP. Although the climate was an important driver of fire hazard during the warm and dry early Holocene, tree cover was consistently the strongest predictor of past biomass burning. In temperate forests, biomass burned was high at ~ 45% tree cover and decreased strongly towards 60% tree cover. In needleleaf dominated forests, biomass burned was highest at ~60-65% tree cover and abruptly declined at >65% tree cover. Biomass burned also increased when arable lands and grasslands reached ~15-20%, although this relationship was highly dynamic depending on land use intensity throughout ignition and fuel type and availability. Our observations cover the full range of Holocene climate variability and land cover changes and illustrates that percentages of land cover is a key predictor of the probability of fire occurrence over timescales of centuries to millennia. We suggest that long-term fire risk may be effectively reduced through land cover management, given that land cover has controlled fire regimes under the dynamic climates of theHolocene