Ecological impacts of the 2004 Indian Ocean tsunami on coastal sand-dune species on Phuket Island, Thailand

Our knowledge of how coastal species react to, and recover from, tsunamis is deficient because of the infrequency of these events, despite the importance of such information for ecological risk assessment of coastal hazards. To elucidate the differences in resilience among species and the successional processes of coastal sand-dune flora after tsunamis, we monitored the ecological impacts of the 2004 Indian Ocean tsunami on coastal sand-dune species on Phuket Island, Thailand. Using 127 floristic inventory datasets, we compared the occurrence, species composition, characteristics, and eco-morphological adaptations of coastal sand-dune species before and after the tsunami. Among the 73 species recognized, the occurrences of 28 changed significantly after the tsunami. The impacts on coastal sand-dune species of non-coastal sand-dune species invading the dunes after the disaster were temporary and minimal, perhaps because of constant coastal stresses such as sand movement and salt spray. Damage to woody species was less than that to herbaceous species. There were clear post-tsunami differences in the successional trajectories of coastal sand-dune flora (particularly herbaceous vegetation) between protected beaches with low-level anthropogenic disturbance and resort beaches. The tsunami-related qualitative variations on each beach were clearly explained not by changes in the Shannon-Wiener diversity index but by differences in species number (i.e., species richness). Numbers of coastal sand-dune species (particularly monophytes and those growing clonally by stolons) decreased significantly on protected beaches after the tsunami. We suggest that the recovery process—including its direction, trajectory, and duration—in coastal sand-dune species after tsunamis depends strongly on the individual beach structure and the degree of anthropogenic disturbance, including trampling pressure and beach development. Evaluation of species in terms of functional traits is effective for assessing sand-dune status after tsunamis.