Spatial distribution patterns of coastal plants along sandy beaches restored by offshore breakwaters in western Japan

Abstract

We investigated the diversity and spatial distribution patterns of coastal plants in relation to coastal microtopography and size of 16 sandy beaches restored by offshore breakwaters and seven natural sandy beaches in Yumigahama, Tottori Prefecture, western Japan. We also used 5×5 m quadrats to survey representative areas of three beaches with offshore breakwaters and one natural beach. The total number of coastal plant species for beaches with offshore breakwaters was 24, and that for natural beaches 20. The incidence of six coastal plants, Ischaemum anthephoroides, Arabis stelleri var. japonica, Zoysia macrostachya, Viola mandshurica var. crassa, Salsola komarovii, and Tetragonia tetragonoides, showed a significant difference between beaches with offshore breakwaters and natural beaches. Logistic regression analysis revealed that five species, Carex pumila, Glehnia littoralis, Sedum oryzifolium, Vitex rotundifolia, and Linaria japonica, all declined in number as the size of the beaches with offshore breakwaters decreased. These results show that the differences in the microtopographic characteristics and disturbance due to uprush waves both affect floral diversity. Thus, while beaches with offshore breakwaters could be important habitats for coastal plants, any conservation measures focusing on these beaches need to be implemented over as wide an area as possible to ensure that a wide variety of microtopographies are available for colonization by coastal plants.