Floristic variation of beach vegetation caused by the 2011 Tohoku-oki tsunami in northern Tohoku, Japan

The infrequency of tsunamis results in a lack of knowledge regarding the impact they have on ecosystems. Comparison of the floristic composition before and after tsunamis using permanent plots is an effective approach to estimate the ecological impacts of tsunamis in coastal environments. Here, we report the floristic changes in beach vegetation in northern Tohoku, Japan caused by the 2011 Tohoku-oki tsunami. Among the beaches studied, we observed differences in the vegetative characteristics of the beach flora, whereas similarities were found in vegetation response patterns, particularly for herbaceous vegetation. No significant interaction was found between the overall number of vascular plant species or the number of non-beach species and the tsunami disturbance; conversely, on beaches that experienced relatively small impacts, the number of typical/characteristic beach species, Pielou evenness index values, and Shannon-Wiener diversity index values were significantly lower after the tsunami. Following the tsunami, the herbaceous vegetation species composition on all of the beaches was characterized by a few non-beach species that are known to tolerate strong anthropogenic disturbances; in contrast, the damage to shrub vegetation was lower than that to herbaceous vegetation. Our findings are similar to what was observed following the 2004 Indian Ocean tsunami in Thailand, suggesting that the initial response patterns of beach vegetation to tsunamis are similar, regardless of the affected climatic zone and species composition. Long-term field monitoring is needed to elucidate post-tsunami recovery, vegetation succession, and the ecological impact of the increase of non-beach species.

► We monitored ecological changes of vegetation after the 2011 Tohoku-oki tsunami. ► Biased succession of vegetation after the tsunami was found on all beaches. ► Initial responses of beach vegetation to tsunamis are common across climatic zones. ► Permanent plots are powerful tools for ecological risk assessment of coastal hazards.