Late Holocene Hyrcanian forest and environmental dynamics in the mid-elevated highland of the Alborz Mountains, northern Iran

Abstract

We present a high-resolution multi-proxy study including pollen, spores, non-pollen palynomorphs, charcoal, loss on ignition, and geochemical analysis from the radiocarbon dated sediment core of Annal Lake. The lake is located at 700 m elevation in the Hyrcanian forest of the Gilan province, northern Iran. Between ca. 1690 and 1450 cal yr BP, a mixed forest with Alnus, Carpinus, Quercus, and Fagus were present, as well as patches of grassland areas around the lake. At ca. 1450 cal yr BP, the forest expanded and reduced the open grassland areas until 65 cal yr BP. Different proxies indicate that humans were present in the studied area since the beginning of the recorded period. However, since 65 cal yr BP, human impact increased markedly by deforestation and cattle grazing, and settlers probably changed from pastoralism to more farmers. Ratios of geochemical elements such as V/Cr, K/Al, Rb/Al, Si/Fe, and Ca/K suggested the warmest period with the higher amount of rainfall and detrital inputs forming a shallow lake between ca. 1690 and 580 cal yr BP. In contrast, a colder and drier period occurred between ca. 580 and 250 cal yr BP, mostly corresponding to the Little Ice Age period. Based on the geochemical element ratios, the highest detrital inputs (Ti), the highest lake level (V/Cr, Rb/Al, K/Al), and the wettest climatic conditions (Ca/Ti) with high rainfall and a relatively stable climatic conditions occurred for the last ca. 250 cal yr BP since the recorded period.