Dispersal and re-establishment of Silaum silaus (L.) in floodplain grassland

The re-colonization of grassland by Silaum silaus was analysed on fields in the Saale River floodplain changed to extensive management in 1989 (restoration grassland). The species was still very rare in 1999 and did not reappear at all in areas distant from seed sources. Soil nutrient content and seedling mortality were studied and compared with adjacent permanently extensive grassland where Silaum silaus was very common. The dispersal capacity was investigated by recording the position of seedlings following artificial introduction of mother plants into restoration grassland. Extractable P and K-values were still little higher in restoration grassland than in permanently extensive grassland, whereas C-t, N-t and N-min-values were lower. The comparison of seedling mortality gave evidence that conditions of establishment were similar. Only few seeds were dispersed beyond 3 m. About 75% of the seedlings were recorded within a circle of 1.5 m around the mother plants. Management and flooding did not increase dispersal distances. No seedling was recorded in dung pats and drift lines. It was concluded that slow dispersal was the main limiting factor of re-colonization by Silaum silaus.