Four millennia of vegetation and environmental history above the Hyrcanian forest, northern Iran

Abstract

Past vegetation, fire, and climate dynamics, as well as human impact, have been reconstructed for the first time in the highlands of the Gilan province in the Alborz mountains (above the Hyrcanian forest) for the last 4,300 cal yrs bp. Multi-proxy analysis, including pollen, spores, non-pollen palynomorphs, charcoal, and geochemical analysis, has been applied to investigate the environmental changes at 2,280 m a.s.l., above the Hyrcanian forest. Dominant steppe vegetation occurred in the study area throughout the recorded period. The formation of the studied mire deposits, as well as vegetation composition, suggest a change to wetter climatic conditions after 4,300 until 1,700 cal yrs bp. Fires were frequent, which may imply long-lasting anthropogenic activities in the area. Less vegetation cover with a marked decrease of the Moisture Index (MI) suggests drier conditions between 1,700 and 1,000 cal yrs bp. A high proportion of Cichorioideae and Amaranthaceae, as well as the reduction of trees, in particular Fagus and Quercus, at lower elevations, indicate human activities such as intense livestock grazing and deforestation. Soil erosion as the result of less vegetation due to dry conditions and/or human activities can be reconstructed from a marked increase of Glomus spores and high values of K and Ti. Since 1,000 cal yrs bp, the increasing MI, as well as the rise of Poaceae and Cyperaceae together with forest recovery, suggest a change to wetter conditions. The occurrence of still frequent Cichorioideae and Plantago lanceolata along with Sordaria reflect continued intense grazing of livestock by humans.

Late Holocene paleoenvironmental changes inferred from multi-proxy studies of the Kholasht-Kouh Lake sediments in the Gilan mountains, northern Iran

“…The human activities showed a reduction during this period, documented with lowest frequency of Cerealia and other human indicator taxa, rarity of the coprophilous spores and macro-charcoal particles. Though, this reduction is opposite to our previous studies at Annal Lake and Pounel mire (Homami Totmaj et al 2020, which showed increased anthropogenic activities. Based on the current settlements (there is a small summer use village in 3.5 km distance to the lake) we may argue that people were always present at several distances to the lake, nevertheless expansion of the forest, resulted in higher arboreal pollen deposition, while reduced presence of the human pollen indicators specially the Cerealia.…”

“…The warm condition during this period, may provided favorable conditions for forest expansion. This forest expansion is also documented in our previous studies from Annal Lake (700 m elevation) and Pounel mire (2200 m elevation) for the same time period (Homami Totmaj et al 2020, about 125 km and 145 km distance to the site, respectively. However, in the KHL record Quercus is the most abundant forest taxon, while in the Annal Lake Carpinus betulus and Alnus (characteristic tree for lower than 1000 m elevations) were the most abundant ones.…”

“…The first investigation from the highlands of the Gilan reconstructed the anthropogenic and environmental changes for the entire late Holocene period on the Pounel mire at 2280 m a.s.l. (Homami Totmaj et al 2020). The study showed that around the Pounel mire steppe was dominant at least for the past four millennia.…”

“…Despite the importance of understanding past interactions between the climate and human activities in this region, the available studies are still insufficient and focused mainly on the coastal plains, especially the central and eastern plains (Naderi Beni et al 2013;Khakpour Saeej et al 2013;Leroy et al 2013Leroy et al , 2019. The western region's (in Gilan province) have not been studied until last decade (Leroy et al 2011;Haghani et al 2015;Homami Totmaj et al 2020;Gu et al 2021). Although the mentioned studies did not cover the whole Holocene period, they shed some light on the vegetation of the western part of the Hyrcanian region.…”

The combined effects of climate and canopy cover changes on understorey plants of the Hyrcanian forest biodiversity hotspot in northern Iran

“…This could be interpreted by various habitat‐specific features in ferns (see Table S4) as some of them prefer to grow and invade disturbed forests or forest openings as well as occur in peat mounds in forest gaps (Amanzadeh et al, 2013; Deljouei et al, 2018; Kooch et al, 2011). It was also shown in some palynological studies of the Hyrcanian forests that fern spores became less frequent whenever the forest canopy recovered (e.g., Homami Totmaj et al, 2020).…”