Preliminary report on the buried seeds of floating islands and bottom of Lake Rawa Pening, Central Java

The formation of floating islands in Lake Rawa Pening originated from the population growth of Eichhornia crassipes. The floating islands dominated by E. crassipes are replaced by Panicum repens and Eriocaulon cinereum in an advanced stage of succession, and Leersia hexandra and Eragrostis amabilis were the dominant species in the final stage of succession on the islands. The soils in several seral stands and silt at the bottom of lake contained many viable seeds. The numbers of seeds and species in 490 cm^3 soil were 45 grains and 19 species in Eichhornia-Sacciolepis stand, 75 grains and 15 species in Panicum-Eriocaulon stand and 60 grains and 7 species in Leersia-Eragrostis stand. The soil at the bottom of the lake also contained considerable numbers of seeds. The floristic composition of the islands differs from that of the buried seeds most of which belong to Cyperaceae. The seeds of E. crassipes were found in the stands in later stages of succession, whereas the species declined in its dominancy of the standing vegetation.