13 巻 (1996) 1 号 p. 1-10
The soil seed bank of a Phragmites australis community was studied in Hakone Sengokuhara, Kanagawa Prefecture, central Japan, in the spring of 1992, the summer of 1993 and the autumn of 1994, and the results were compared with the above-ground vegetation studied in the summer of 1994 and the summer of 1995. The autumn sample had the largest number of seed grains and species, and showed a significant difference from the samples of the other two seasons. Kyllinga gracillima and Carex capillacea were the most abundant in all samples. The soil seed bank was very similar to above-ground vegetation in species composition, though they were not always similar in density. Species were classified into the following four categories based on seasonal variation and vertical distribution of buried seeds, and the existence of seedlings. The first group, including Isachne globosa, Astilbe microphylla and so on, consists of species with seeds reserved in upper layers only and no seedlings. This means that they regenerate at a safe site, if their seeds are dropped there by chance. Microstegium vimineum var. polystachyum, Hydrocotyle ramiflora and so on were comprised in the second group characterized by species with seeds reserved in upper layers only and seedlings. These species pass the unsuitable season as seeds that are adapt to severe environment. Kyllinga gracillima, Carex capillacea and so on belong to the third group characterized by seeds reserved in all layers and no seedlings. These seeds remain in the soil as a reserve in case of unpredictable vegetational disturbance. The fourth group consists of species such as Viola verecunda, Lycopus uniflorus and Mosla dianthera that have seeds reserved in all layers and seedlings. These species likely have two kinds of seeds: one contributes to maintainance and dispersion of the population and the other remain as a reserve in the soil in case of disturbance. It appears that plants are usually regenerated vegetatively and that the soil seed bank plays only a small role in the regeneration of a Phragmites australis community. However, seedlings originating from buried seeds must contribute to regeneration when a serious disturbance occurs.