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

Contribution of non-pollen palynomorphs to reconstructions of land-use changes and lake eutrophication: case study from Lake Jaczno, northeastern Poland

Analysis of non-pollen palynomorphs supplemented by pollen analysis, microcharcoal analysis and geochemical data from laminated sediments from Lake Jaczno were used to establish different phases of land-use in the catchment between c.a. AD 1840 and AD 2013. The results show that during the first eighty years the vicinity of the lake was heavily deforested. During this period erosional inputs caused accumulation of abundant fungal spores, indicators of pastures and natural fertilizers (manure) as well as of corroded pollen grains and charcoal. Gradual regeneration of forest cover took place after World War II, when expansion of pioneer trees occurred (Betula, Salix, Carpinus, Populus). At the same time, a considerable increase in the lake trophy was observed, leading to the changes in phytoplankton and macrophyte communities: a decrease in the proportion of Botryococcus and an increase in the Nymphaea alba population. The non-pollen palynomorphs analyses indicate the substantial human impact that caused changing local environmental conditions, compatible with the results based on pollen analysis and geochemical data

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