In order to explore the methods of recovering native grasses into exotic vegetation, the response of riparian vegetation to the removal of the above-ground shoots and/or litter of Solidago gigantea in a flood plain in Hokkaido, northern Japan, was investigated. The four treatments were: the removal of the above-ground shoots of S. gigantea (A); the removal of the litter of S. gigantea (L); the removal of both the above-ground shoots and litter of S. gigantea (AL); and a control (C). The vegetation cover and S. gigantea cover decreased in the A and AL treatments and increased in the L and C treatments. The understory plant cover increased in the A and AL treatments, but did not change in the L and C treatments. The increases in the understory cover in the A and AL treatments were associated with increases in Phalaris arundinacea. The seedling emergence of P. arundinacea was promoted by AL. In a greenhouse, the S. gigantea litter tended to decrease the seed germination of P. arundinacea. The AL treatment also increased the abundance of the other exotic plant, Solidago altissima. The continuous removal of the above-ground shoots and litter of S. gigantea long term is effective for promoting the recovery and emergence of native riparian grassland vegetation. However, this method also promotes the recovery of other exotics.