Long-term interactions between Mediterranean climate, vegetation and fire regime at Lago di Massaciuccoli (Tuscany, Italy)

1. A Holocene sedimentary sequence from a coastal lake in the Mediterranean area (Lago di Massaciuccoli, Tuscany, Italy, 0 m a.s.l.) was sampled for pollen and microscopic charcoal analyses. Contiguous 1-cm samples represent an estimated time interval of c. 13 years, thus providing a high-resolution sequence from 6100 to 5400 cal. years BP. 2. Just before 6000 cal. years BP, sub-Mediterranean and Mediterranean forests were present together with fir (Abies alba), a submontane species that is today absent at low altitudes in the Mediterranean. A sharp vegetational change occurred after 6000 cal. years BP involving a drastic decline of Abies alba around the site. 3. Time-series analyses suggest that increased fire activity at this time caused a strong decline in Abies alba, a highly fire-sensitive species. During 100 years of higher fire incidence, diverse (predominantly evergreen) forest communities were converted to low-diversity fire-prone shrub communities. 4. Cross-correlations reveal that fire during the mid-Holocene hindered the expansion of holm oak (Quercus ilex), the most common tree species today in Mediterranean environments. While the factors that triggered the Holocene expansion of this species in the Mediterranean area are unclear, our results do not support the hypothesis that fire was key for holm oak expansion. 5. Diatom analyses of the same sediment core provide an independent palaeoenvironmental proxy for palaeoclimatic reconstruction. A change in the eutrophy and salinity of the lake occurred just before 6000 cal. years BP, suggesting that a climatic shift towards aridity may have triggered the observed change in hydrology and possibly also in fire regime. 6. Over the millennia fire has decisively contributed to the establishment of the present fire-adapted vegetation type (macchia). Native fire-sensitive species were displaced or repressed, and arboreal vegetation became less diverse. Combined ecological and palaeoecological data may help to assess possible future scenarios of biosphere responses to global change. Our results imply that the forecasted global warming and fire increase may trigger irrecoverable biodiversity losses and shifts in vegetational composition within a few decades or centuries at most. In particular, fire and drought-sensitive vegetation types, such as the relict forests of Abies alba in the Apennines, seem particularly threatened by large-scale displacement.