Holocene forest dynamics in northwestern Romnania

Pollen analyses and AMS radiocarbon measurements were carried out on peat deposits from the former crater lake Preluca Tiganului, located in a mid-altitude area of the Gutaiului Mountains (NW Romania), in order to reconstruct the postglacial vegetation history. At the Lateglacial/Holocene transition the open vegetation was replaced by forest, suggesting a fast response to climatic warming. The rapid expansion of Pinus, Betula and later Picea may be due to their existence in the area during the Lateglacial. At approximately 11 250 cal. yr BP, the dense forest was composed primarily of Ulmus and some Picea, Betula and Pinus. A small population of Ulmus might also have survived in the area during the Lateglacial. At 10750 cal. yr BP, Quercus, Tilia and Fraxinus, followed by Corylus at c. 10200 cal. yr BP, expanded significantly in the forest. The delay of approximately 550 years in their establishment, as compared to the expansion of Ulmus, was probably due to their immigration from more distant localities. Between 9300 and 5750 cal. yr BP, the forest became denser and was composed of Corylus (dominating), Ulmus, Quercus, Tilia, Fraxinus and Picea. At 5750 cal. yr BP Carpinus became established and expanded, possibly as a response to higher temperatures. At 5200 cal. yr BP, Fagus became locally established, and expanded from about 4800 cal. yr BP, possibly as a result of moist climatic conditions, although human activities cannot be excluded. From 4000 cal. yr BP to the present, Fagus dominated the woodlands, and all other deciduous trees (except for Carpinus and Quercus) became greatly reduced. Evidence of human influence on the local vegetation is low for this time period, but becomes more evident in the pollen stratigraphy around 2300 cal. yr BP. This is reflected by a decrease in forest diversity and an increase in pasture and forest grazing.