Sediments of Last Glacial and Holocene age from two different locations in the basin of Lago di Pergusa have been palynologically and isotopically investigated. New data have been integrated with those available from previous researches carried out by the authors. This study indicates once more that Lago di Pergusa was and still is very sensitive to climate changes. In particular, during the Last Glacial, it played an important role in preserving the biodiversity as thermophilous and mesophilous taxa never completely disappeared. In particular, Zelkova pollen indicates that the distribution area of this tree (still living as a relic plant in south-eastern Sicily) was wider during the Last Glacial, where its last spread is found around 20,000 years BP. The delta(18)O record, mirroring the arboreal concentration trend, confirms the climate inferences based on vegetation features. Both the Late Glacial and the Postglacial reforestation periods show slower vegetation dynamics and forest development than expected, with trends mirroring the slow and sustained decline of delta(18)O record. The Younger Dryas oscillation is not pronounced in any of the lacustrine palaeoenvironmental proxies, its termination occurring around 11, 100 cal. years BP. The opening of the woodland recorded by a slow trend ranging from the Neolithic (around 8000 cal. years BP) to the Eneolithic (few centuries before 4000 cal. years BP) seems to be a natural forest clearance and not due to human impact. Anomalies in pollen, microcharcoals and positive correlations between delta(18)O and AP curves are found after a climate change occurring at 4500 years BP, and interpreted as a signal of human impact. The new delta(18)O data presented in this paper throws new light to propose this hypothesis, confirming an early aridification trend detected from pollen, and a relatively late human impact inferred from fire dynamics in this central and montane region of Sicily. (C) 2007 Elsevier Ltd and INQUA. All rights reserved.