Divergent fire history trajectories in Central European temperate forests revealed a pronounced influence of broadleaved trees on fire dynamics

Abstract

Fire occurrence is driven by a complex interplay between vegetation, climatic, landform and human factors making it challenging to separate the individual effect of each variable. Here we present a reconstruction of the Holocene biomass burning history of two regions located in the Central European temperate zone that differ in the timing of the Middle Holocene expansion of broadleaf-dominated forest communities. This allowed us to investigate the effect of biotic changes on past fire activity. Multiple-site charcoal accumulation records were used to estimate regional-scale trends in biomass burning and to compare them with major trajectories of vegetation development. Extensive 14C-dated soil charcoal records collected within both regions were amalgamated using a cumulative probability function to identify a stand-scale proxy of past fire occurrence. Our results suggest that rising vegetation productivity driven by rapid Early Holocene climate amelioration enhanced biomass burning. The increased fire activity during this period was driven by both a drier- and warmer-than-present climate and easily flammable fuels produced by conifer-dominated vegetation. We identified an inhibiting effect of the concomitant Fagus sylvatica expansion on levels of biomass burning that occurred asynchronously between our mountain and mid-elevation sandstone regions 6500 cal yr BP and 4900 cal yr BP, respectively. The amount of compositional change in plant communities was more related to the transformation of major vegetation types than to fluctuations in fire activity levels. The divergent timing of the fire decline in response to the Fagus sylvatica expansion implies biotic control over biomass burning that is independent of a direct climatic influence.