In the Mediterranean region, Corsica represents one of the most important hotspots of biodiversity, partly due to the high number of endemics species. This region is also one of the most affected by forest fires worldwide. The present vegetation is adapted to a wide range of disturbance regimes, but a change in fire frequency or intensity in the future may severely affect ecological resources and other socio-economical aspects. Here, we study the dynamics of vegetation–human–fire interactions for the past 12,000 years as recorded by Lake Bastani (Corsica, France). We used well-dated sedimentary records of charcoal, pollen and fungal spores to infer past fire regime, land cover and pastoral activities, respectively, and we compared our results with charcoal records from two other Corsican lakes (Nino and Creno, respectively). Our results suggest that climate and natural fires were the main factors shaping the landscape before 5000 cal. BP. Then, the extraordinary diversity of the current Corsican vegetation has been mainly promoted by human activities on the island (i.e. deforestation and pastoralism) at least from the Bronze Age (3500 cal. BP). The top of our record shows a sharp decrease in fungal remains ( Sporormiella-type), usually associated with pastoral activities, which could be attributed to the land abandonment occurring since a few decades.

Currently, indexes from the Fire Weather Index System (FWI) are used to predict the daily fire hazard, but there is no reliable index available in the Mediterranean region to be compared with paleofire records and check for their long-term reliability. In order to assess the past fire hazard and the fire-season length, based on data availability and requirements for fire index computation, we first chose and tested the efficiency of the Drought Code (DC) in Corsica (the main French Mediterranean fire-prone region) over the current period (1979–2016). We then used DC as a benchmark to assess the efficiency of the Monthly Drought Code (MDC) and used it to assess the Fire-Season Length (FSL), which were both used to characterize the fire hazard. Finally, we computed the Holocene MDC and FSL based on the HadCM3B-M1 climate model (three dimensional, fully dynamic, coupled atmosphere-ocean global climate model without flux adjustment) datasets and compared both index trends with those from proxies of paleofire, vegetation, and land use retrieved from sedimentary records in three Corsican lakes (Bastani, Nino, and Creno). Our strategy was to (i) assess fire hazard without the constraint of the daily weather-data requirement, (ii) reconstruct Holocene fire hazard from a climate perspective, and (iii) discuss the role of climate and human fire drivers based on the MDC-Paleofire proxy comparisons. Using both the Prométhée fire database and the ERA-Interim climate database over Corsica for the current period, we showed that DC values higher than 405 units efficiently discriminated fire-days from no-fire-days. The equivalent threshold value from MDC was set at 300 units. MDC and FSL indexes calculated for each of the past 11 millennia Before Present (11 ka BP) showed high values before 7 ka BP (above 300 units for MDC) and then lower values for the mid- to late Holocene (below 300 units for MDC). Climate appeared as a key driver to predict fire occurrences, promoting fires between 11 and 8 ka BP when summers were warmer than the current ones and reducing fire hazard after 7–6 ka BP due to wetter conditions. Since 5 ka BP, humans have taken control of the fire regime through agro-pastoralism, favoring large and/or frequent events despite less fire-prone climate conditions. The current fire hazard and fire-season length computed over the last few decades (1979–2016) both reported values that were respectively higher and longer than those assessed for the previous six millennia at least and comparable for those before 7 ka BP. For the next decades, due to climate warming associated with land abandonment (fuel accumulation) and the increase in human-related sources of ignition, we can expect an increase in fire hazard and larger fire events.

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Global Paleofire Working Group 2: Paleofire Knowledge for Current and Future Ecosystem Management; Saint-Hippolyte, Quebec, Canada, 10–14 October 2017

In the Mediterranean basin, Corsica (French island) harbours among the best-preserved Mediterranean forest ecosystems and its high biodiversity could be threatened by the climate and disturbance-regime changes due to the global warming. This study aims i) to estimate the future climate-related fire hazard in Corsica for the current century (2020–2100) based on two RCP scenarios (RCP4.5 and RCP8.5), and ii) to compare the predicted trends with the entire Holocene period for which fire hazard has previously been assessed. An ensemble of future climate simulations from two IPCC RCP scenarios has been used to compute the Monthly Drought Code (MDC) and the Fire Season Length (FSL) and to assess the level of fire hazard assessment. Here, we show that the MDC and the FSL would both strongly increase over the next decades due to the combined effect of temperature increase and precipitation decrease in the Corsica region. Moreover, the maximum Holocene FLS (7000 to 9000 years ago), will be reached (and even exceeded depending upon the scenario) after 2040. For the first time in the Holocene, we may be confronted to an increase in the number of fire-prone months driven by climate combined with many human-caused ignitions. This combination should increase the burned area from 15–140%. For the next 30 years, the game seems to be already played as both RCP scenarios resulted in similar increase in fire hazard intensity and duration. It is thus mandatory to reconsider fire-management and fire-prevention policy to mitigate the future fire risk, and its catastrophic consequences for ecosystems, population, and economy.

Aim In recent decades, a surge in the number of significant and uncontrolled wildfires has occurred worldwide. Global warming may amplify this trend and threaten most ecosystems worldwide. Deciduous forests are characterized by high plant diversity, and understanding their long‐term dynamics is crucial to anticipate changes in these ecosystems during ongoing global warming. The aim of this study is to understand how European beech forests have colonized the inner Eastern Carpathians and how changes in fire regime and human activities have affected their biodiversity. Location Inner Eastern Carpathian Mountains, Slovakia. Taxon Plantae, gymnosperms, angiosperms. Methods Peat core was extracted from the centre of Ďurova mláka mire in 2018. A multi‐proxy approach has been applied to investigate the development of beech forest. Charcoal analysis has been done each centimetre to reconstruct the fire signal. Pollen analysis has been done at 2 cm resolution to reconstruct the vegetation composition and dynamics, and the variation in palynological richness (PRI), evenness and turnover has been analysed. Macro‐remains analysis has been performed at 10 cm resolution to add more information about the local vegetation. Results Low diversity spruce forest was dominant until 5200 cal. BP during a fire‐prone period due to specific climatic conditions (drier climate than the following period). The higher fire frequency and intensity following this period is simultaneous with the first expansion of Fagus which indicate that Fagus could occupy post‐fire habitats, at least at the local scale. However, its dominance coincided with major gaps in fire events from 3900 cal. BP. The PRI has increased during the transition from spruce to beech forest highlighting the importance of beech forests in maintaining plant biodiversity. However, the stronger increase in the richness is synchronous with the increase in human activities around 2000 cal. BP, and then 350 cal. BP. Main Conclusions Climate‐driven fire frequency has been a natural driver of vegetation changes in the Carpathians by promoting the emergence of high diversified beech forest. These changes were significantly modified by later increase in human activities.