The effect of Riparian land use on the occurrence and abundance of Japanese knotweed Reynoutria japonica on selected rivers in South Wales

Five selected rivers in South Wales were surveyed at 236 sites, each consisting of a 500-m length of both banks. For each unit, riparian land use and abundance of Reynoutria japonica were estimated. The data were arranged in a contingency table with four abundance categories (0, 1–10, 11–50, >50% cover) and six land uses (natural and semi-natural; grazed; woodland; intermediate woodland; wasteground; land drainage works) and tested for association (G-test statistic). Riparian land use was found to significantly (p<0·01) affect the abundance of the plant. On waste ground and land drainage works R. japonica occurred more frequently than expected at a high abundance, and on grazed land and in natural/semi-natural communities of river banks it occurred less frequently and in low abundance. The results are in accordance with the ecology of the plant. Implications for nature reserve management are considered.