A multi-proxy view of exceptionally early postglacial development of riparian woodlands with Ulmus in the Dniester River valley, western Ukraine

This article presents the first multi-proxy study of palaeoecosystem changes during the Late Weichselian and Early Holocene in western Ukraine. The site is a former oxbow lake situated in the Dniester River valley (western Ukraine). We hypothesised that this area may have been one of the nuclei for the Holocene expansion of elm (Ulmus), a primary arboreal taxon in riparian woodlands, in the Central and Eastern European lowlands. Our study was undertaken on a profile encompassing the period ca. 12,900-9880 cal. BP. We applied selected palaeobotanical, palaeozoological and geochemical analyses. During the Younger Dryas the area was dominated by well-developed Pinussylvestris-Betula woodlands. Drier habitats were overgrown by Juniperus shrublands and steppe communities. Patches of tundra with Betulanana were also present. Ulmus started to spread on the lower river terraces before ca. 11,840 cal. BP i.e., during the late Younger Dryas, which suggests this area as a nucleus for its Holocene expansion. A chironomid-based reconstructed mean July temperature (MJT) of 15-17 °C is suggested during the Younger Dryas. The main Ulmus expansion started ca. 11,160 cal. BP and its optimum in local woodlands lasted until ca. 10,340 cal. BP, when Pinussylvestris rapidly expanded. The reconstructed MJT varied between 18 and 21 °C during the Ulmus optimum; however, it rapidly declined to 16 °C around ca. 10,800 cal. BP. Fire activity increased before ca. 10,870 cal. BP, concurrent with the climate warming at the Younger Dryas-Holocene transition, but did not affect the population of Ulmus, a taxon intolerant of fires. Wildfires probably affected patches of steppe vegetation and Pinussylvestris-Betula woodlands occupying higher elevations of the valley and watersheds. However, changes in the fire activity may have stimulated Ulmus retreat at ca. 10,340 cal. BP.