Human-induced fires and land use driven changes in tree biodiversity on the northern Tyrrhenian coast.

The history of fires in southwestern Tuscany (Italy), from the Colline Metallifere to the coast of northern Maremma, is presented with an observational perspective at local and regional scale. The area was studied as part of the nEU-Med project, which investigates resources management, agricultural practices and political strategies in two coastal plains, the Cornia and Pecora valleys, between the 7th and 12th centuries AD. Four cores, selected for palaeoenvironmental studies, were analysed for microcharcoals (C3 and C7 - Cornia Valley, ∼last 7500 years; P3 and P4 - Pecora Valley, ∼last 3200 years). Microscopic charcoal particles are ubiquitous and particularly high in the most recent pollen zone of the diagrams: most records belong to the 10–50 μm size class (>90%), followed by the 50–125 μm size class (<7%) and the rest are records of size >125 μm. The last size class includes large microcharcoals indicating local fires. Several potential fire activity increases (PFAIs) are visible as peaks in the diagrams. In the Cornia Valley, ancient phases of local fires were recorded at ∼5600 BC; not strictly local fires were scattered in the valley at ∼4600 BC, ∼3500 BC, and until ∼400-1450 AD, when the peaks testify to the spread of fires with increasing human activity. In the Pecora Valley, scattered local fires are observed at ∼900 BC, between ∼300 BC and ∼50 BC, and in the later phases from ∼400 AD to ∼1050 AD. Therefore, the increase in fires is visible in the last millennium in both valleys. Fire was probably used to open the landscape, as fluctuations of pollen curves of mixed oakwood (mainly deciduous Quercus) and Erica suggest. The extensive presence of shrubby heather vegetation testifies to the occurrence of repeated fires. In the Cornia Valley, besides oaks, the main fuel source were Corylus avellana and Ostrya carpinifolia/Carpinus orientalis. In the Pecora Valley, cores show a synchronous increase in AP and NAP pyrophytes until ∼400-500 AD, followed by a decrease in AP pyrophytes. Considering forest dynamics, a too short return time for fires affects the biodiversity of woody plants, as woods could not fully recover and several tree species may not have reach sexual maturity, resulting in less sprouting and recolonization. In these valleys, the recovery of large-sized microcharcoals, the presence of heather shrub vegetation, and the trend of AP/NAP pyrophytes suggest that fires have increased significantly in the last ∼1200 years (∼800-1400 AD). [ABSTRACT FROM AUTHOR]