The Species Composition of Buried Seeds of Seashore Vegetation Disturbed by the Great East Japan Earthquake and Tsunami in Northern Tohoku, Japan

Abstract

The 2011 Tohoku-oki tsunami damaged most sandy coastlines in Tohoku, Japan, and sandy beach vegetation was extensively disturbed. Buried seeds contribute greatly to vegetation recovery and ecological succession in general. Knowing the impact of tsunamis on seed banks and drift seeds is important in estimating the recovery of destroyed vegetation, but such information is lacking. Therefore, we examined buried seed and drift seed populations to elucidate the potential for the recovery of species diversity on sandy beaches. We collected samples of sandy sediment and debris in Iwate and Aomori prefectures, northern Tohoku, Japan. We estimated the seed populations in these samples using both the germination and seed-floating methods. In December 2011, the species composition of buried seeds in sandy sediment was very simple; ruderal plants comprising Chenopodium, Compositae, and Gramineae were remarkable. Although we found no coastal plant seeds in December 2011 sediment, eight coastal plants, Atriplex subcordata, Salsola komarovii, Setaria viridis var. pachystachys, Boehmeria splitgerbera, Leymus mollis, Linaria japonica, Carex kobomugi, and Glehnia littoralis, emerged in November 2012. Concerning alien plants, four species were observed in 2011—Bidens frondosa, Erigeron canadensis, Erigeron annuus, and Atriplex prostrata—and Plantago lanceolata was seen in 2012. The coastal species S. komarovii and the alien species Cakile edentula occurred in a debris sample in 2011. In the following year, we identified many types of coastal plants, alien plants, and other species. The seed bank that existed before the tsunami appears to have been mostly lost, and its contribution to vegetation recovery in 2011 would therefore have been small. The species composition and diversity of the seed bank after the tsunami will depend on the introduction of dispersed seeds directly from living vegetation and/or via the ocean.