Root Effect of Three Vegetation Types on Shoreline Stabilization of Chongming Island,Shanghai

Coastal erosion is currently a major problem along the southern coast of Chongming Island,Shanghai.To enhance the erosion protection ability of coastal shelterbelts,two woody tree species,Taxodium ascendens and Salix babylonica,were planted separately into Phragmites australis + Scirpus mariqueter communities in 2006.Two years later,we investigated whether either of these experiments reduced erosion and increased stability in the native herbaceous plant community.We also examined soil stability and root length density under T.ascendens added,S.babylonica added and native herbaceous vegetation conditions along an intertidal gradient from the soil surface to a depth of 40 cm in each experiment,thus to determine the capacity of T.ascendens and S.babylonica to contribute to shoreline stabilization.Topsoil under the native vegetation had greater stability at the middle and higher intertidal zones because its soil stability index and root length density were significantly higher than in the T.ascendens or S.babylonica planted communities.The effect of T.ascendens on soil stability was not generally better than that of the native vegetation.Only at the 20-30 cm soil depth of the middle intertidal zone and in the 10-20 cm layer of the higher intertidal zone the soil stability index and root length densities under the T.ascendens added condition were significantly higher (P < 0.05) than those of the native vegetation.The S.babylonica planted soil had greater stability in the deeper soil layer than the soil under either the native vegetation or the T.ascendens added condition,and its soil stability index and root length density were significant higher (P < 0.05) than those of other vegetation conditions at the 30-40 cm soil depth for the lower intertidal zone and at the 20-40 cm layer for middle and higher intertidal zones.