Survival characteristics of buried seeds 10 years after the eruption of the Usu volcano in northen Japan

In the crater basin of the Usu volcano, where the vegetation has almost completely been destroyed by 1977–1978 eruptions, a study was conducted in 1987 to determine the survival characteristics of buried seed populations. A total of 17 618 seeds were extracted from six 25-L former topsoil blocks by a flotation test. Data showed that even after 10 years burial by 65–140 cm volcanic deposists, 16.6% of the seeds, representing 25 species, were viable. There were few predators in the former topsoil below the thick volcanic deposits. Seed volume of most species was less than 2.0 mm 3 and smaller seeds had a greater rate of survival than larger seeds. Seed survival rates of Poa annua, Rumex obtusifolius, Alopecurus aequalis var. amurensis, and Viola grypoceras were positively correlated with the thickness of volcanic deposits, suggesting that the most important factor for seed survival is stable soil temperature with little diurnal fluctuations. Absence of light may be an important variable in seed survival, but this factor did not sufficiently explain survival under the thick volcanic deposits.