Abstract
Coreopsis lanceolata keeps a number of buried seeds in top soil. It would be most effective to remove the top soil for preventing the buried seeds from germinating and new individuals from spreading, but the treatment of the removed soil which still contains numerous seeds of Coreopsis lanceolata would be a problem. Therefore, we carried out an experimental removal of top soil and monitored the removed soil in the dry gravel riverbed of the middle stream of the Kiso River, in order to examine the effectiveness of removing buried seeds and the reduction rate of buried seeds in the removed soil. The reduction rate of buried seeds due to the removal of top soil is approximately 80%, and remaining 20 % seems to be because the removal of top soil was incomplete and some were dropped out of the removed soil. Moreover, we attempted to mulch the removed soil by using the weed control sheet and to prevent the buried seeds from germinating. The reduction rate of buried seeds which survived in the removed soil is approximately 50 % in two years.
