Piloting an Unmanned Aerial Vehicle to Explore the Floristic Variations of Inaccessible Cliffs along Island Coasts

Abstract

Coastal cliffs are important in plant ecology as a unique frontier between terrestrial and marine ecosystems. This study piloted close-range photogrammetry with an unmanned aerial vehicle (UAV) to clarify floristic patterns using 26 inaccessible coastal cliffs in a warm-temperate, preserved island (area: 6.5 km2). UAV-based flora data were analyzed in terms of cliff aspect (Type-N: northwestern aspect of the island, Type-S: other island aspects) and elevation. The studied coastal cliffs contained 94 flora taxa, of which 13 and 12 taxa were found from either Type-N or Type-S cliffs only. Type-S cliffs retained a larger number of epiphyte and evergreen species but a smaller number of deciduous species than Type-N cliffs (p < 0.05), and 4 out of 8 detected epiphyte species dwelled in Type-S cliffs only. Additionally, the elevation of coastal cliffs was positively related to the proportion of tree and epiphyte species (r = 0.608, p < 0.001) but negatively related to the proportion of herbs (r = −0.649, p < 0.001). These patterns corresponded to differing microclimates such as the severity of cold and dry conditions during winter. We expect that UAV-based approaches will help understand plant ecology under harsh, challenging environments beyond the speculation with traditionally accessible sites only.