Holocene palaeovegetation of the Northwestern Pirin Mountains (Bulgaria) as reconstructed from pollen analysis

Pollen analysis and radiocarbon dating were performed on a sequence 150 cm deep from a peat bog (Mozgovitsa, 1800 in above sea-level) in the Northwestern Pirin Mountains, Bulgaria. The palaeovegetational reconstruction focused on the main stages of forest development starting from approximately 8700 years BP. The vegetational response to the amelioration of the climate in the Early Holocene until 7500 cal BP resulted in the spread of birch forests (Betula pendula) that occupied large areas at high altitudes forming the upper tree-line together with pine (Pinus sylvestris, Pinus peuce, Pinus mugo), juniper (Juniperus), alder (Alnus), and willow (Salix). Below them were mixed deciduous oak forests with some Ulmus, Tilia, Corylus, Carpinus, and Acer. The continuous Early Holocene pollen record of mesophyllous demanding trees (Abies alba, Fagus sylvatica and Picea abies), though in low frequencies, suggests that groups of these trees survived in environmentally favourable habitats with sufficient moisture such as deep mountain valleys. The most important change in the vegetation cover started ca. 7500 cal BP when birch forests declined and coniferous vegetation dominated by Pinus sylvestris, Pinus peuce and Abies alba invaded the slopes. The spread of the conifers and the expansion of their areas presume an increase in humidity and precipitation, and the development of soils with humic horizons. The last trees to establish after ca. 4000 cal BP in the study area were Picea abies and Fagus sylvatica. Their expansion in the Northwestern Pirin Mountains started at the Subboreal/Subatlantic transition ca. 3000 cal BP when average temperatures dropped and precipitation increased. Deforestation in historic times resulted in the appearance of new pasture land and the lowering of the upper tree-line. (C) 2003 Elsevier Science B.V. All rights reserved.