Exploring potential drivers of European biomass burning over the Holocene: a data-model analysis

AimTo reconstruct spatial and temporal patterns of European fire activity during the Holocene and to explore their potential drivers, by relating biomass burning to simulated biotic and abiotic parameters. LocationEurope. MethodsHolocene fire activity was investigated based on 156 sedimentary charcoal records from lakes and peat bogs across Europe. Charcoal data covering the last 9000 years were statistically compared with palaeoclimate data derived from the Max Planck Institute for Meteorology/University of Wisconsin-Madison Earth System Model, with vegetation and fire indices simulated with the dynamic vegetation model lpj-guess and with two independent scenarios of past anthropogenic land-cover change. ResultsThe combined sedimentary charcoal records suggest that there was little fire activity during the early and the middle Holocene compared with recent millennia. A progressive increase in fire frequency began around 3500cal. yr bp and continues into the late Holocene. Biomass burning rose sharply from 250cal. yr bp onwards, reaching a maximum during the early Industrial Era and then declining abruptly. When considering the whole Holocene, the long-term control of fire is best explained by anthropogenic land-cover change, litter availability and temperature-related parameters. Main conclusionsWhile the general patterns found across Europe suggest the primary role of vegetation, precipitation and temperature-related parameters in explaining fire dynamics during the early Holocene, the increase in fire activity observed in the mid-late Holocene is mainly related to anthropogenic land-cover changes, followed by vegetation and temperature-related parameters. The 20th-century decline in biomass burning seems to be due to increased landscape fragmentation and active fire suppression policies. Our hypothesis that human activities played a primary role in Holocene biomass burning across Europe could be tested by improved palaeoclimate reconstructions and more refined representations of anthropogenic fires in climate and vegetation models.

Quantifying the effects of land use and climate on Holocene vegetation in Europe

Jed Oliver Kaplan

Early agriculture can be detected in palaeovegetation records, but quantification of the relative importance of climate and land use in influencing regional vegetation composition since the onset of agriculture is a topic that is rarely addressed. We present a novel approach that combines pollen-based REVEALS estimates of plant cover with climate, anthropogenic land-cover and dynamic vegetation modelling results. This is used to quantify the relative impacts of land use and climate on Holocene vegetation at a sub-continental scale, i.e. northern and western Europe north of the Alps. We use redundancy analysis and variation partitioning to quantify the percentage of variation in vegetation composition explained by the climate and land-use variables, and Monte Carlo permutation tests to assess the statistical significance of each variable. We further use a similarity index to combine pollen based REVEALS estimates with climate-driven dynamic vegetation modelling results. The overall results indicate that climate is the major driver of vegetation when the Holocene is considered as a whole and at the sub-continental scale, although land use is important regionally. Four critical phases of land-use effects on vegetation are identified. The first phase (from 7000 to 6500 BP) corresponds to the early impacts on vegetation of farming and Neolithic forest clearance and to the dominance of climate as a driver of vegetation change. During the second phase (from 4500 to 4000 BP), land use becomes a major control of vegetation. Climate is still the principal driver, although its influence decreases gradually. The third phase (from 2000 to 1500 BP) is characterised by the continued role of climate on vegetation as a consequence of late-Holocene climate shifts and specific climate events that influence vegetation as well as land use. The last phase (from 500 to 350 BP) shows an acceleration of vegetation changes, in particular during the last century, caused by new farming practices and forestry in response to population growth and industrialization. This is a unique signature of anthropogenic impact within the Holocene but European vegetation remains climatically sensitive and thus may continue to respond to ongoing climate change. (C) 2017 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2017

Quantifying the effects of land use and climate on Holocene vegetation in Europe

Jed Oliver Kaplan

Pergamon-Elsevier Science Ltd2017