Case Study: Chongming Dongtan National Nature Reserve, China
Chongming Dongtan National Nature Reserve is a Ramsar site located on the eastern tip of Chongming Island in Shanghai, China. It is situated on the East Asian-Australasian Flyway. Invasive cordgrass Spartina alterniflora was introduced in 1995 and by 2012 covered over 2,000 ha of the salt marsh in the reserve. This resulted in extensive ecological change across tidal flats, making them unsuitable for foraging and roosting shorebirds. Various methods for controlling S. alterniflora were tested and evaluated in Chongming Dongtan. For example, in 2007, Yuan et al. (2011) tested the effect of waterlogging and cutting to control S. alterniflora . They found that managed waterlogging initially reduced S. alterniflora biomass and seed production, but that S. alterniflora later showed rapid adaptation to the long-term waterlogging stress. However, when three months of managed waterlogging was followed by cutting the above-ground part of S. alterniflora during the flowering period (July), S. alterniflora was successfully eradicated. There was no regrowth of S. alterniflora in the following years, however, when the hydrodynamic regime was restored to the area, S. alterniflora reinvaded from neighbouring areas. In 2013, a large-scale restoration project covering 2,400 ha was launched in Chongming Dongtan NNR. This project cost ¥1.3 billion Chinese Yuan (US$ 186 million; February 2024 conversion), with one of the major goals being to eradicate S. alterniflora . There were two main sites in the project region, one that was enclosed by a cement dike and another that was partially enclosed with a sediment dike. The dike was built as an attempt to guarantee the eradication of S. alterniflora . Within the enclosed area, S. alterniflora was controlled through cutting the plants and flooding the marshes. The plan is for the constructed levee to be allowed to deteriorate, or deliberately breached, so that the area can return to tidal inundation (Mark Dixon, pers. comm.). Barrier fences outside the engineering area stimulated sediment accretion, forming a tidal mudflat <2 m above sea level. This was used for revegetating Scripus mariqueter, a common native species.
What was the impact on Spartina ?
From 2012 to 2016, S. alterniflora cover dropped substantially from 2,000 ha to 729 ha. However, large areas of S. alterniflora remain intact outside the reserve (over 1,315 ha in 2018) on Chongming Island (Zhang et al. , 2020).This serves as a source for subsequent S. alterniflora re-invasion and poses a threat to the restoration efforts in Chongming. In 2016 – 2017, a field experiment was conducted using Gallant herbicide (Haloxyfop-R- methyl) as an emergency control for re-invading S. alterniflora (Zhao et al. , 2020). The researchers found the highest tested dose of 2.70 g/m 2 to be the most effective, removing 100% of small patches at 92% of continuous swards. Lower doses (0.45 – 1.35 g/m 2 ) were less successful, removing less than 40%. The researchers also found that applying herbicide in July/August resulted in 100% mortality, while S. alterniflora was able to recover rapidly when applied in May.
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