Fire frequency and intensity associated with functional traits of dominant forest type in the Balkans during the Holocene

Disturbances by fireare among the most important processes that shape forest dynamicsand diversity. However, the long-term variability of firedisturbance regimes in many European forests and specifically in the mountains of the Balkan Peninsula is not well understood. Here, we present the first Holocene record of fire regimesbased on macrocharcoal morphologies in combination with pollen-based reconstruction of forest dynamicsand fire-related strategies of prevailing mountain forests in the Rila Mountains, Bulgaria. While biomass burning followed the main trends in climate, the frequency and intensity of firewere strongly linked to fire-related coping strategies of dominant tree taxa (resisters, avoiders or invaders). Frequent firesof low intensity between 12,000 and 9000 cal year BP were concurrent with the dominance of invaders (Betula, herbs, ferns). Intermittent occurrence of low- and high-intensity surface and crown fireswith longer return intervals between 9000 and 4000 cal year BP was associated with codominance of resister (Pinus sylvestris, Pinus peuce, Pinus mugo) and avoider ( Abies albaand Picea abies) forest types, whereas a lengthening of the firereturn interval over the past 4000 years was linked to increased abundance of P. abies. As a rising number of fireepisodes may drive land cover towards more fire-adapted plant communities and towards less intense fireevents, we expect increased dominance of invaders ( resproutersthat rapidly reach maturity stage) as well as resisters (properties protecting from firedamage) under future warmer and drier climate. This study also shows the potential of combining charcoal morphologies with pollen records to track variability in fireintensity and plant functional attributes over long timescales that are also relevant to forest management stakeholders.