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Accueil du site → Doctorat → Allemagne → 2020 → Studies on vegetation-, fire-, climate- and human history in the mid- to late Holocene - a contribution to protection and management of the forest-steppe-biome in the Mongolian Altai

Georg-August Universität zu Göttingen (2020)

Studies on vegetation-, fire-, climate- and human history in the mid- to late Holocene - a contribution to protection and management of the forest-steppe-biome in the Mongolian Altai

Unkelbach Julia

Titre : Studies on vegetation-, fire-, climate- and human history in the mid- to late Holocene - a contribution to protection and management of the forest-steppe-biome in the Mongolian Altai

Auteur : Unkelbach Julia

Université de soutenance : Georg-August Universität zu Göttingen

Grade : Doctor rerum naturalium 2020

Résumé
In this thesis, several sedimentological archives from Altai Tavan Bogd National Park are studied to reconstruct the vegetation-, fire-, climate- and human history of the forest-steppe biome in the Mongolian Altai. The research is carried out to improve the understanding of the dynamics and variability of this sensitive ecosystem and its unique biodiversity. Previous palynological or palaeoecological work from the Mongolian Altai is sparse, yet important for an implementation of sustainable land use as well as protection and management of the species-rich vegetation in the Altai region. The main goals of this research are to reconstruct past vegetation and to investigate the role and extent of climate, fire and anthropogenic impact on environmental change. A multi-site approach of five environmental archives (lacustrine and peat) from different locations and elevations within the forest-steppe biome (below, within and above the forest belt) is applied to obtain as much information as possible. Multi-proxy analyses including palynological and sedimentological proxies (pollen, NPPs, charcoal, diatoms and XRF-scanning) were used on the radiocarbon dated sediment archives. During the mid- and the beginning of the late Holocene (4,300 to 1,000 (2,000) cal yr BP) the vegetation in the area was characterized by open coniferous forest and high-mountain steppe indicating rather warm and humid conditions. In the further course of the late Holocene, steppe communities expanded noticeably favoring a colder and more arid climate. During the last approx. 70 years an increase in tree and shrub vegetation indicates a warming climate and a higher availability of water due to permafrost and glacier degradation in the high mountains. Regarding the human history in the Mongolian Altai, the period from 2,000 to 1,000 cal yr BP represents a transition phase from hunters and gatherers to a nomadic herding lifestyle. Coprophilous fungi reconstructions show that grazing intensified around 1,000 cal yr BP, possibly also favoring the expansion of steppe. High-resolution data show that changes in human occupation due to political shifts and changing Mongolian settlements had an impact on the vegetation in the area, especially during Mongol Empire (744 to 582 cal yr BP). Regardless of specific settlement periods, short-term changes in climatic conditions favored shifts in grazing activities. In the Mongolian Altai, fires play a tangential role. However, at around 1,000 cal yr BP the fire frequency increased in accord with growing anthropogenic impact and climate aridity. An episode of low fire activity persists since around 150 cal yr BP. Major local variances occurred regarding the time frame and extent of steppe expansion and grazing activities in the soil archive within the forest belt and with respect to the fire frequency in the peat archive above the upper forest line. The applied multi-proxy approach highlights the value of the reconstruction of several independent proxies to examine various aspects of an ecosystem in the same archive, despite of that the interpretation of results is challenging. Additionally, the multi-site study offers the best possibility to distinguish between local environmental signals and regional trends.

Mots clés  : Mongolia ; vegetation history ; climate history ; human activity ; nature conservation ; forest-steppe-ecosystem ; multi-proxy-approach

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Page publiée le 27 décembre 2020