Abstract
BackgroundThe plant communities within reservoir drawdown zones are ecologically important as they provide a range of ecosystem services such as stabilizing the shoreline, improving water quality, enhancing biodiversity, and mitigating climate change. The aim of the study was therefore to identify the major environmental factors affecting these plant communities within the drawdown zone of the Soyangho Reservoir in South Korea, which experiences a monsoonal climate, and thereafter to (1) elucidate the plant species responses and (2) compare the soil seedbank composition along main environmental gradients.ResultsTwo main environmental gradients affecting the plant community structure were identified within the drawdown zone; these were a vertical and longitudinal gradient. On the vertical dimension, a hydrological gradient of flood/exposure, the annual-dominated plant community near the water edge changed to a perennial-dominated community at the highest elevation. On the longitudinal dimension from the dam to the upstream, plant species composition changed from an upland forest-edge community to a lowland riverine community, and this was correlated with slope degree, soil particle size, and soil moisture content. Simultaneously, the composition of the soil seedbank was separated along the vertical gradient of the drawdown zone, with mainly annuals near the water edge and some perennials at higher elevations. The species composition similarity between the seedbank and extant vegetation was greater in the annual communities at low elevation than in the perennial communities at higher elevation.ConclusionsThe structures of plant community and soil seedbank in the drawdown zone of a monsoonal riverine reservoir were changed first along the vertical and secondly along the longitudinal gradients. The soil seedbank could play an important role on the vegetation regeneration after the disturbances of flood/exposure in the drawdown zone. These results indicate that it is important to understand the vertical and longitudinal environmental gradients affecting shoreline plant community structure and the role of soil seedbanks on the rapid vegetation regeneration for conserving and restoring the drawdown zone of a monsoonal reservoir.
Highlights
The plant communities within reservoir drawdown zones are ecologically important as they provide a range of ecosystem services such as stabilizing the shoreline, improving water quality, enhancing biodiversity, and mitigating climate change
Two main environmental gradients were detected from the biplot of environmental variables: (1) elevation and its related exposure duration and (2) distance from the dam and its related angle of slope, soil particle size, and moisture content (Fig. 3a)
In the correspondence analysis (CCA) of the drawdown zone vegetation (Fig. 4), the species biplot showed a gradation from perennials (e.g., C. orbicularis var. brachylepis, Equisetum arvense, P. arundinacea, Pteridium aquilinum var. latiusculum) located mainly at the negative end of Axis 1 through to annuals (e.g., P. nodosa, P. trigonocarpa, B. frondosa, Panicum dichotomiflorum) positioned around the center through to the positive end of Axis 1 (Fig. 4a, b)
Summary
The plant communities within reservoir drawdown zones are ecologically important as they provide a range of ecosystem services such as stabilizing the shoreline, improving water quality, enhancing biodiversity, and mitigating climate change. The plant communities of the drawdown zone could be expected to be affected by exposure/flood cycles along the vertical gradient (e.g., Nilsson and Keddy 1988; Bao et al 2015) as well as by the environmental changes along the longitudinal gradient in riverine reservoirs Regeneration of this vegetation from the soil seedbank is likely to be important along these gradients, especially in areas with frequent and intense disturbance of exposure/ flooding (Zhang et al 2016). Information regarding the effects of both vertical and longitudinal gradients on the plant communities within the drawdown zone is severely limited, especially for those reservoirs of riverine and dendritic shape with wide water level fluctuations This is likely to occur where there is a monsoonal climate. A large drawdown zone has been formed due to a very wide annual range of water level fluctuation with a maximum of 37 m between 1974 and 2017 (Han River Flood Control Office 2018 )
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