Abstract
The role of seeds in habitat expansion and the contribution of seed banks were examined for populations of Robinia pseudoacacia L. in the Akagawa river basin, Yamagata Prefecture, Japan. Vegetation map analysis determined that around one third of patches of R. pseudoacacia had emerged from seeds rather than from root suckers, and were distributed where root suckers could not invade, i.e. on a river holm or situated more than 60 m from the nearest conspecific patch. During a 5-year period between 1999 and 2004, 30 patches emerged, of which 12 were considered to be derived from seeds. Hard seeds of R. pseudoacacia tend to form soil seed banks, but in this area most hard seeds were found in soil under R. pseudoacacia stands. However, at sites of other types of vegetation, such as Salix and Juglans stands, and at denuded sites, dormant seeds were almost entirely absent. This study's findings indicate that there is self-replacement of the soil seed bank of R. pseudoacacia following destruction of existing stands due to disturbance, but that self-replacement scarcely contributes to the generation of new populations. This suggests that stands established at newly disturbed sites tend to result from seedling emergence from seeds without dormancy or where dormancy was removed during dispersal by water in streams. Hence, decreased regeneration from dispersed seeds should also be taken into consideration in the population control of R. pseudoacacia.
