In order to clarify the primary succession in Sakurajima, Japan, we studied the volcanic vegetation on the Showa, Taisho, Anei, and Bunmei lava flows, which erupted from Mt. Sakurajima in 1946, 1914, 1779, and 1471, respectively, and the natural forest on pumiceous sand. The species composition was compared among forests I, II, III, IV and V on the Showa, Taisho, Anei, and Bunmei lava flows and pumiceous sand, respectively. Forests I and II were recognized as middle seral stages in the primary succession. Forests III and IV, which had similar dominant species, species composition, and species richness, were recognized as at the same seral stage in the secondary succession. Forest V, which was characterized by the absence of many lucidophyllous forest elements, was at a later or climax stage. The species richness (number of lucidophyllous forest elements) and years of succession on the Showa and Taisho lava flows had a high positive relationship. The sere in the primary succession in the warm temperate zone (lucidophyllous forest zone) consisted of five seral stages from the lichen and bryophyte community to the herbaceous community, the Pinus thunbergii forest, the Machilus thunbergii forest, and the Castanopsis sieboldii forest. It probably takes about 600 years to arrive at the climax stage (the Castanopsis sieboldii forest) in the primary succession.

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In most Japanese seepage marshes, which are oligotrophic wetlands that accumulate no or little peat on the surface and are formed by seepage water, different types of plant communities create spatial mosaic patterns. The vegetation patterns and spatial changes in environmental factors (groundwater level, surface sediment and its movement) were surveyed and compared in Ooneyama Marsh, a seepage marsh in Central Japan (Gifu Prefecture). To detect movement of surface sediment, ^<137>Cs was used as a tracer. The domains of three key species groups in the marsh were ranged according to gradient of groundwater depth. The Rhynchospora species were in the highest area, followed by the Moliniopsis japonica and the woody species more than 1 m height (shrub). Pinus densflora, the dominant species in the shrub, was distributed all over the marsh, but it grew poorly in communities on wet sites and well on dry sites. The surface sediment in high groundwater areas was eroded and thin, and that in low groundwater areas was accumulated and thick. These results suggest that, in this seepage marsh, groundwater level was an important determinant of vegetation type. Moreover, groundwater level varied spatially in the marsh as a result of secondary factors such as movement of surface sediment. This physiographic structure seemed to be involved in generating the vegetation pattern in the seepage marsh. Vegetation succession in the seepage marsh may occur through changes in groundwater supply.

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Crypsinus hastatus (Thunb.) Copel. is a fern species that grows on dry and steep slopes. However, establishing this species on such slopes is difficult because of the difficulties pertaining to obtaining sufficient water supply by the gametophytes and because the spores are susceptible to washout by rainfall. Therefore, in this study, we focused on the presence of bryophyte communities that would facilitate the establishment of fern gametophytes. We investigated the relationship between bryophyte coverage and the presence of young sporophytes of C. hastatus. Young fern sporophytes occurred more frequently in grids with high bryophyte coverage than in those with low bryophyte coverage. This result suggests that bryophyte communities prevent spore washout caused by rainfall. Another possible reason that young fern sporophytes occurred more frequently in areas populated by bryophyte communities was that these communities may maintain wet conditions suitable for the growth and fertilization of gametophytes. Thus, the results indicate that it would be easier to establish growth of C. hastatus in areas populated by bryophyte communities than on bare ground.

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