Single-species versus mixed-species community: which one is better for shore stabilization. A case study of Chongming Island, China

There are five vegetation communities for shore stabilization on the southern coast of Chongming Island: a reed (Phragmites australis) community, a 4-yr-old Salix babylonica–Phragmites australis community (4Sb), an 8-yr-old S. babylonica–P. australis community (8Sb), a 4-yr-old Taxodium ascendens–Phragmites australis community (4Ta), and an 8-yr-old T. ascendens–P. australis community (8Ta). One major question is which is better for shore stabilization: the reed community (a single-species community) or 4Sb, 8Sb, 4Ta and 8Ta (mixed-species communities)? The soil stability index (K) and root length density (RLD) were selected as indicators for evaluating soil stability in response to water erosion. There are two main types of shore facing downward erosion and erosion scarp retreat along the southern coast of Chongming Island, and the erosion period may occur from March to August (scenario 1) or October to December (scenario 2). The assumed erosion period is scenario 1, and 4Sb is the most suitable plant community for preventing erosion scarp failure and mitigating shoreline retreat because it has the greatest K and RLD in the 20–50-cm deep soil layer among all of the vegetation communities within all intertidal zones. Additionally, 4Sb and 8Ta provide the best protection for reducing downward beach face erosion compared to the other vegetation types in the lower intertidal zone (LIT). At the middle intertidal zone (MIT) and higher intertidal zone (HIT), the reed community is optimal for protecting the shore face because it has the greatest K and RLD at 0–20-cm soil among the five vegetation communities in March–April and July–August within the MIT and HIT. Under scenario 2, 4Sb is still the most suitable type for reinforcing the scarp and preventing shoreline retreat. With respect to shore face downward erosion, 8Ta might provide the best protection for beach surfaces within the intertidal zones because it had the greatest K and RLD at 0–20-cm depth among the five vegetation types in November–December within the LIT, MIT and HIT.