A contribution to the postglacial vegetation history of the Rila Mountains, Bulgaria: The pollen record of Lake Trilistnika

Pollen analysis of sediments from the glacial Lake Trilistnika (2216 m) in the Northwestern Rila Mountains (Bulgaria), supplemented by 13 radiocarbon dates, allowed the reconstruction of the palaeoenvironment and vegetation history in postglacial time. The exact time of the cirque glacier retreat is still under discussion but the lake was free of ice before 15,000 cal. BP, when sedimentation of gray silt began. The lateglacial vegetation, composed of Artemisia, Chenopodiaceae and Poaceae, with isolated stands of Pinus and Juniperus–Ephedra shrubland, dominated during the stadials and partly retreated during the Bølling/Allerød interstadial complex. The afforestation in the early Holocene (11,500–7800 cal. BP) started with the distribution of pioneer Betula forests with groups of Pinus (P. mugo, P. sylvestris and P. peuce) at mid-high altitudes, and Quercus forests with Tilia, Ulmus, Fraxinus, Corylus below the birch zone. The change to more humid and cooler climate ca. 7800–7500 cal. BP favored the vertical migration of Abies, P. sylvestris and P. peuce. The establishment of Fagus sylvatica took place after 5200 cal. BP, when pure or mixed beech communities were formed. The last tree which invaded the coniferous belt between 4300 and 3400 cal. BP was Picea abies. The first expansion maximum of spruce was recorded after ca. 2700 cal. BP. The vegetation development in historical times was also influenced by human interference, indicated by the continuous presence of pollen anthropogenic indicators such as Triticum, Secale, Hordeum, Plantago lanceolata, Rumex, Scleranthus, Juniperus.