Between Rear and Leading Edge - Juniper woodlands on the southern Tibetan Plateau - A high mountain forest-line-ecosystem under environmental change
Because of the eco-systematic significance of forests and their close link to the climatic history a large part of paleo-ecological research has dealt with the history of forests during the Pleistocene climatic oscillations. On the basis of these efforts the global patterns of vegetation and forest...
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|Summary:||Because of the eco-systematic significance of forests and their close link to the climatic history a large part of paleo-ecological research has dealt with the history of forests during the Pleistocene climatic oscillations. On the basis of these efforts the global patterns of vegetation and forest histories could largely be reconstructed especially by means of pollen analysis, macrofossils and finally phylogeography. However, in recent years an increasing number of studies have shown that microrefugia in temperate and boreal areas, often called cryptic refugia, had been overlooked by traditional methods. As a consequence the importance of these microrefugia for the conservation of genetic diversity, as well as their role in postglacial re-expansions has not been adequately acclaimed. Furthermore it became obvious in recent years that the early anthropogenic influence on the forest histories was not sufficiently reflected in the paleo-ecological sciences. This potentially led and still leads to a considerable bias in climatic parameters derived from paleo-ecological reconstructions. In this context the cumulative dissertation here presented deals with the forest history of the Tibetan Plateau. It postulates a special significance of high-mountain areas for the preservation of microrefugia. In the included four articles both classical as well as molecular genetic methods were used to reconstruct the forest history of the Southern Tibetan Plateau as exemplified by the Tibetan juniper forests. In paper I current forest remains were mapped and characterized. According to these findings forest and woodland relics were found in large parts of the southern Tibetan Plateau. Natural reproduction on many of these sites, as well as reforestation trials showed that the area is potentially forested under current climatic conditions. In paper II charcoal analytical investigations showed that up to the late Holocene the Tibetan juniper forests had a broader distribution range. The reduction to the current extent was interpreted as a consequence of anthropo-zoogenic pressure in combination with dessiccation. However, to support these findings high resolution charcoal data bases will be needed in the future. The necessary anthracological potential in the geo-archives of the southern Tibetan Plateau could be demonstrated through this work. By means of molecular genetic analysis paper III could show that unlike former assumption the juniper forests of the southern Tibetan Plateau survived in microrefugia on the plateau platform itself throughout today’s range. Furthermore it could be shown that the Himalayan juniper populations did not contribute significantly to the postglacial expansion on the plateau. The observed patterns along with the known mutation rates in the used chloroplast markers indicate a late tertiary origin of the spatial genetic patterns. In addition, the numerous decentralized microrefugia as well as the high number of private haplotypes therein demonstrate the potential importance of high mountain areas with their heterogenic topographies and microclimates for the conservation of genetic resources. Finally paper IV provided technical resources for subsequent analysis of genetic resources within the Tibetan juniper forests. By means of next generation sequencing a set of microsatellite marker were developed that will enable us to analyze gene flow, as well as nuclear genetic diversity. Furthermore these markers are a foundation to realize the research agenda proposed in the outlook of the dissertation.|