Holocene vegetation, fire, climate dynamics and human impact in the upper Orkhon Valley of the Khangai Mountains, Mongolia

Abstract

The Upper Orkhon Valley, located in the Khangai Mountains of Central Mongolia, is mainly covered by a forest-steppe ecosystem. This is an interesting area to study because its vegetation dynamics might have been influenced by climatic and anthropogenic drivers. This study investigates the dynamics of vegetation (pollen), human activity (pollen and NPP) and fire activity (macro-charcoal) from a lacustrine sediment core from lake Shireet Naiman Nuur, covering the last 7400 cal yr BP. The results of the pollen analysis showed a continual and constant decline of tree species in favour of the development of grasslands. Fire activity was more intense (high peak magnitude) during the mid Holocene, while it became more frequent but less intense from 5000 cal yr BP onwards, when herbaceous taxa became more present. The NPP analysis suggest that the study site was free of human activity from 7400 to 3500 cal yr BP, whereas the traces of the development of human societies that took place in the Orkhon Valley, such as pastoralism and grazing activities, have been demonstrated by the increase in coprophilous fungi and the Poaceae Cerealia-type pollen around 3200 cal yr BP, although its impact seems to have remained low.