Diversity and Above-Ground Biomass Patterns of Vascular Flora Induced by Flooding in the Drawdown Area of China's Three Gorges Reservoir

Abstract

Hydrological alternation can dramatically influence riparian environments and shape riparian vegetation zonation. However, it was difficult to predict the status in the drawdown area of the Three Gorges Reservoir (TGR), because the hydrological regime created by the dam involves both short periods of summer flooding and long-term winter impoundment for half a year. In order to examine the effects of hydrological alternation on plant diversity and biomass in the drawdown area of TGR, twelve sites distributed along the length of the drawdown area of TGR were chosen to explore the lateral pattern of plant diversity and above-ground biomass at the ends of growing seasons in 2009 and 2010. We recorded 175 vascular plant species in 2009 and 127 in 2010, indicating that a significant loss of vascular flora in the drawdown area of TGR resulted from the new hydrological regimes. Cynodon dactylon and Cyperus rotundus had high tolerance to short periods of summer flooding and long-term winter flooding. Almost half of the remnant species were annuals. Species richness, Shannon-Wiener Index and above-ground biomass of vegetation exhibited an increasing pattern along the elevation gradient, being greater at higher elevations subjected to lower submergence stress. Plant diversity, above-ground biomass and species distribution were significantly influenced by the duration of submergence relative to elevation in both summer and previous winter. Several million tonnes of vegetation would be accumulated on the drawdown area of TGR in every summer and some adverse environmental problems may be introduced when it was submerged in winter. We conclude that vascular flora biodiversity in the drawdown area of TGR has dramatically declined after the impoundment to full capacity. The new hydrological condition, characterized by long-term winter flooding and short periods of summer flooding, determined vegetation biodiversity and above-ground biomass patterns along the elevation gradient in the drawdown area.

Biodiversity of arbuscular mycorrhizal fungi in the drawdown zone of the Three Gorges Reservoir under different fertilization histories

“…The drawdown zone of the TGR represent one of the most endangered wet and dry intermittent ecosystems because of the intermittent submergence time, prolonged duration of flooding and new drawdown zone (spanning up to 30 m in elevation), resulting in the loss of historic vegetation and changes in many other ecological conditions such as a loss of vegetation, bank collapse and greenhouse gas emissions (Wang et al 2014). To restore and protect the reservoir ecosystem, many studies have focused on the description of local plant biodiversity.…”

“…Many field surveys have shown that a large proportion of the pre-dam riparian vegetation failed to adapt to this major change (New and Xie 2008). Those species gradually disappeared or died under the strong selection pressures of alternative submerged and barren land conditions, leading to the formation of a bare drawdown zone within the TGR basin (Wang et al 2014). Consequently, widespread soil erosion and landslides caused by vegetation degradation occurred in the permanently submerged areas of TGR area (Ye et al 2012;Lei et al 2014).…”

“…Consequently, widespread soil erosion and landslides caused by vegetation degradation occurred in the permanently submerged areas of TGR area (Ye et al 2012;Lei et al 2014). A number of studies have investigated the effects of dam-building on riparian vegetation (Shafroth et al 2002;Wantzen et al 2008;Ye et al 2012), where flood duration and timings have been proven to be important factors affecting reservoir vegetation (Wang et al 2014). Currently, submergence-tolerant species have been transplanted to the drawdown zone of the TGR (Luo et al 2006;Ye et al 2013).…”

Soil Organic Carbon Shapes AMF Communities in Soils and Roots of Cynodon dactylon under Anti-Seasonal Drying-Wetting Cycles

“…The water table between 145 m and 175 m (impounded level) of the newly-formed drawdown zone has created a total area of~400 km 2 water body along the Three Gorges Reservoir (TGR) since the completion of a 185 m high dam in the middle stream of Yangtze River in 2010 [1]. As a consequence of flood control and hydropower manipulation, a 30 m hydro-logically seasonal up-and-down regime has been switched down to less than 140 m water table by emptying the downstream water during the natural flooding (wetting) in summer, but up to 175 m water table by storing the water during the natural un-flooding (drying) in winter.…”

“…The conversion from natural habitats into agricultural lands has resulted in vegetation loss, soil degradation, and negative influences on nutrient biogeochemical cycles [19]. Such changes in the vegetation cover and soil characteristics have been one of the leading causes for the loss of plant biodiversity [1,18,20]. In cultivated farm lands, AMF population, taxa composition, and diversity tend to be decreased when compared with their natural ecosystems [18,21,22].…”