Structure, reproduction and flood-induced dynamics of riparian Tugai forests at the Tarim River in Xinjiang, NW China (original) (raw)
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Excessive withdrawal of water for farmland irrigation, and water losses from water reservoirs and channels, have caused water deficit problems along the Tarim River in Northwestern China. Especially, the lower reaches have been severely threatened since the 1950s, and are experiencing a drastic increase in the mineralisation of the river water. Additionally, large scale deposition of aeolian sand and dust is another major threat for the Tarim Riparian Ecosystem (TaRiEc). This development reached its “climax” with the desiccation of the Taitema Lake in 1972, and the “climax” was well expressed by severe degradation of the TaRiEc, which is in turn predominately characterized by the dying of Populus euphratica stands. All these developments led to the initiation of the “EcologicalWater Diversion Project” (EWDP). The main objective of this project is to ensure a constant water supply to the lower reaches of the Tarim River via the water transfer both from the Bosten Lake catchment and from Tarim’s upper and middle reaches. In this study, the processes and trends of the vegetation change during this period of intermittent water transfer were examined on the basis of remote sensing data. The results show that with the water transfer only some of the P. euphratica trees reached a more vital state. Common hypotheses about factors influencing the tree vitality under stressful conditions deal with the water level in the river, the groundwater level and the distance of the trees from the river. However, soil and sediment, as well as micro-relief conditions also play an important role and take influence on the vitality of the trees. The main objective of the present study was to analyse the features of soil and sediment concerning water passage and water storage processes in near surface and subsurface positions of the lower Tarim Riparian Ecosystem. For that purpose, 2010 and 2011 field and laboratory analyses of soil and sediment profiles were performed. Laboratory results comprise grain size measurements, pore size distribution, total organic content (TOC) and data from XRD-measurements on the soil’s mineral composition for all studied sites within the lower Tarim study area and for selected ecosystem types as well. These parameters allow conclusions about water storage and water passage conditions, which play a key role for water availability and water supply of P. euphratica trees. Besides single soil and sediment parameters, such as salt content and mineral composition, layer types (vertical sequence of soil horizons and sediment layers) have been identified as leading factors determining near surface and subsurface water passage and water storage features of the Tarim Riparian Ecosystem.
Plant Ecology, 2010
The drawdown zone of the Three Gorges Reservoir Region was assumed to be completely formed in 2009 and the water level would range from ~145 m in flood season (summer) to ~175 m during non-flood season (winter). The soil seed bank is an important propagule source for vegetation restoration. In order to evaluate the potential of the soil seed bank to revegetate the drawdown zone of this region, we examined the quantitative relationships between the germinable soil seed bank and the established vertical and horizontal vegetation patterns. A total of 45 soil samples at four sites was collected to examine seed bank density, species richness, and composition using the seedling-emergence method. Forty-five species (from 20 families) germinated from the soil seed bank, and the average seed density was 4578 m−2. The seed bank was dominated by annual plants, suggesting reestablishment of some above-ground species was plausible. However, most established woody plants and perennials were absent from the seed bank indicating a low probability of reestablishment for non-annuals through the seed bank. Thus, due to low species compositional similarity to extant vegetation and the dominance of annual plants, the soil seed bank had a low potential to restore pre-dam vegetation in the drawdown zone of the Three Gorges Reservoir Region, but its potential as a propagule source should be considered regarding the management of the drawdown zone for vegetation cover.