Revegetation of a native species in a newly formed tidal marsh under varying hydrological conditions and planting densities in the Yangtze Estuary

The extent of the Chinese endemic salt marsh community characterized by the sedge, Scirpus mariqueter, which is identified as the most favorable habitat for local biodiversity, has been shrunk due to the rapid expansion of exotic Spartina alterniflora. Based on an ecological engineering aimed at annihilating this invasive species, the increases in newly formed tidal mudflats have made the revegetation of native S. mariqueter possible. In this study, the experiments of S. mariqueter revegetation were examined to assess strategies of site selection in terms of the importance of hydrological regimes. Also, three levels of planting density were also conducted in order to assess their cost-effectiveness. To mitigate the impacts of strong hydrological disturbance on the tidal mudflat, soil microcosms consisting of corms of S. mariqueter were used for planting. The results indicated that the differences in sedimentary rates and tidal wave energy during the initial establishment period significantly influenced the outcome of succession. A moderate sedimentary rate was shown to help the persistence of planting materials, which, in turn, benefitted the colonization of S. mariqueter seedlings by vegetative tillering and rhizome growth underground. However, a heavy sedimentary rate during the early growing season failed to support the establishment of S. mariqueter and destroyed the adaptive mechanism of plants to burial stress, further resulting in the failure of revegetation practices. Regardless of the planting density, a burial depth of approximately 15-20. cm represents a tolerant threshold for the survival of S. mariqueter seedlings. At the same time, a medium planting density appears to a cost-effective way to establish the native species in the newly formed mudflats, because the high-level shoot density was achieved with the medium planting density relative to the high planting density. We suggested that restoration ecologists should take these findings in relation to site selection and cost-effectiveness into careful consideration when planning further large-scale revegetation in the Yangtze estuary.