Abstract: The dynamics of grasses in herb layer on beaches with snails and inhibition effects of Sapium sebiferum and Pterocarya stenoptera on snails were studied. Individual quantity of Paederia scandens(X² = 12.8 ) and Oenanthe javanica (X² = 11.2) are positively, and that of Leonurus artemisia, Equisetum arvense, Rumex acetosa, Calystegia hederacea and Astragalus sinicus are negatively correlated with the density of snails(a<0.02 ). After the flooding period,the mortality of snails on beaches treated with leaves of Pterocarya stenoptera and Sapium sebiferum is increased by 43.3% and 44.1%, respectively.

Key words: Pterocarya stenoptera, Sapium sebiferum, Plant allelopathy, Oncomelania hupensis, stable hydrogen isotope, tree dieback, sap flow, Populus simonii, water source