Palynological reconstruction of beech (Fagus orientalis Lipsky) forest history in ‎central ‎Hyrcanian region over the past 1400 years

Palynological analysis and radiocarbon dating of a peat core from a mire on 1314 m a.s.l altitude in the Alborz Mountains enabled the reconstruction of the vegetation history of the central Hyrcanian forests over the past 1400 years. This palaeopalynological record indicates that Fagus orientalis and Carpinus betulus were the most abundant tree species in the surrounding forest stands and were accompanied by Quercus castaneifolia, Ulmus glabra and Acer velutinum. Alnus subcordata must have persistently been the most abundant tree species at local scale, i.e., on and in the immediate vicinity of the mire. However, this species substantially declined during the periods 1400-1350, 1250-1050 and 450-300 BP, most likely as a consequence of local hydrological changes. Also, Pterocarya fraxinifolia, which was a main local element until a few centuries ago, decimated probably following a climatic cooling and/or drying. In periods where beech was dominant, i.e., 1250-1100 BP, 900-750 BP and in the last 450 years, the stands surrounding the mire were closed canopy and rich in (tree) species. These time spans were also characterized by the sporadic occurrence of shade-intolerant invasive species in the forest floor. Climatic changes and anthropogenic activities must have decisively influenced the structure and composition of the forest stands over the last 1400 years. This was particularly the case during the periods 1350-1250 and 700-550 BP, when a substantial decrease of beech and canopy cover led to the expansion of opportunistic invasive species, such as upland ferns, Artemisia and chenopods, and to a lesser extent Plantago lanceolata.