Soil tillage effect on the control of invasive Spartina anglica in a coastal wetland

Spartina anglica, an invasive marsh grass, was designated as a harmful marine organism in 2016 due to its ability to stabilize mudflats and reduce macrobenthic diversity. To control such invasive species, physical, chemical, or biological methods can be applied while chemical methods are prohibited by law due to ecological disruption. However, the preferred methods of soil tillage, cutting, and native plant restoration for managing S. anglica have rarely been analyzed. To compare the methods, we performed 9 treatments with four replicates, comprising control, different frequencies of clipping (once and twice) and tilling (once and twice), and different densities (50 and 100 seedling) of restoration of the native plants Suaeda japonica and Phragmites australis. To evaluate the severity of disturbance, we measured coverage, stem density, average plant height, and above-ground biomass for 2 years. We found P. australis and S. japonica did not successfully establish or survive due to niche differences and the inherent biological features of Spartina. However, physical removal had a stronger effect than interspecific interaction. Two cutting treatments in the early and the late growing season reduced plant height and biomass of S. anglica by 6 and 34%, respectively, compared with the control treatment at the rapid vegetative growth stage in the following year. We also found that two tillage treatments reduced biomass, plant cover, and stem density by 32%, 38%, and 83%, respectively, in the following year. In the study site, managing invasive species such as S. anglica is best achieved by physically destroying the plant using soil tillage while attempting to restore native species had marginal control effects.