Ecology, Spatial Distribution, and Utilization of the Tugai Vegetation at the Middle Reaches of the Tarim, River Xinjian

The Tugai vegetation, composed of Tugai forests, Tugai shrubs, and reeds, is the typical floodplain vegetation of the Central Asian deserts. The largest expansions of Tugai vegetation used to cover the floodplains of the Amu Darya, the Syr Darya, and the Tarim River. However, due to extensive land reclamation projects in the Soviet Union and China beginning in the 1950ies, most of the Tugai forests and reeds were cleared to make room for irrigation farmland. With increasing water demands for irrigation, the surface water runoff declined, the river discharges dwindled, and the groundwater levels dropped, so that large areas of Tugai forests, shrubs, and reeds became subjected to severe water shortages and drought. The largest and most natural Tugai forests stands are located at the middle reaches of the Tarim River, which was also the reason for establishing the Tarim Huyanglin Nature Reserve there in 1983. This is where the Tarim River has formed an inland delta with a rich mosaic of Tugai forest stands. During the time of this study in 2004, dikes were built all along the Tarim's middle reaches except for the northern riverbank between Yengi Bazar and Iminqäk. Recently built weirs now regulate the influx of water into the river branches of this inland delta.The key-stone species along the Tarim's middle reaches are Populus euphratica for Tugai forests, Tamarix species for Tugai shrubs, and Phragmites australis for reeds. All these species are able to endure the arid climate as phreatophytic plants, i.e. plants which, instead of saving water, continuously tap the groundwater. The generative reproduction of these species takes place on moist riverbanks devoid of vegetation. The natural conditions of such germination sites are created during the annual floods which reshape the river course and moisten the riverbanks. Once rooted and established, Populus euphratica and Tamarix ramosissima can grow on sites with groundwater levels deeper than 10 m.The nature reserve and the adjacent areas which are planned to become protected as well were selected as the study area for this thesis. The objective was to investigate the Tugai vegetation in its most natural state. It was hypothesized that groundwater depth and salt contents in the groundwater are the limiting site factors for individual plants of the Tugai vegetation once they have become established. It was also assumed that the typical desert river dynamics plays a crucial role in the reproduction and succession of the Tugai vegetation.