Late-Glacial and Holocene forest dynamics at Steregoiu in the Gutaiului Mountains, Northwest Romania

Abstract

Pollen analyses and AMS 14C measurements were performed on lacustrine sediments and peat deposits from the former crater lake Steregoiu in a mid-altitude area in the Gutaiului Mountains in NW Romania in order to provide a detailed reconstruction of the vegetational development of the area during the Late-Glacial and Holocene. The bottom sediments are siliciclastic and were deposited probably during the Full Glacial, which is characterised by open patchy vegetation consisting of a mosaic of shrubs, herbs, and ungrown grounds. Around 14 700 cal yr BP an open Pinus– Betula forest expanded, at the same time as organic-rich lake sediments started to be deposited. This change was likely a response to the first deglacial warming phase at the beginning of the Bølling period, or GI-1e, in the GRIP event stratigraphy. Between 13 750 and 12 950 cal yr BP an open forest dominated by Betula, Picea, Pinus, and Ulmus developed in the area. The forest composition implies rather warm climatic conditions, which may correspond to the Allerød, or GI-1c–GI-1a. Around 12 950 cal yr BP the forest retracted, and at 12 600 cal yr BP open patchy vegetation became re-established. These changes imply a return to significantly colder conditions, which may correspond to the Younger Dryas, or GS-1. At 11 500 cal yr BP Betula, Pinus, and Alnus quickly responded to the temperature rise, characterising the beginning of the Holocene. Within a few hundred years, around 11 300 cal yr BP, Ulmus and Picea became re-established and a mixed forest type expanded. Quercus, Tilia, and Fraxinus likely arrived at around 10 750 cal yr BP, and from about this time Betula, and Pinus started to diminish. Around 10 500 cal yr BP a dense mixed forest dominated by Ulmus, Picea, Quercus, Tilia, and Fraxinus had developed in the area. Corylus probably became locally established around 10 500 cal yr BP, but it did not expand until 10 200 cal yr BP. Tilia and Fraxinus were locally important until 8600 cal yr BP, when Picea gained renewed importance and the lake became completely overgrown. Picea was probably an important constituent in the carr forest at the site as well as in the upland forest. Around 4800 cal yr BP Fagus and Carpinus became important in the local stand, apparently without any major disturbance of the forest. Until around 3400 cal yr BP the forest was highly diverse, but when Fagus eventually expanded, Ulmus, Tilia, Picea, and Corylus diminished. From about 2200 cal yr BP onwards Fagus has been the local forest dominant, but some Quercus and Carpinus individuals have been present as well. Pollen evidence for human influence on the local vegetation is comparatively scant. The area may have been used for forest grazing from about 1050 cal yr BP, but the grazing pressure was probably low until ca. 300 cal yr BP.