A Comparative Study of the Floristic Diversity and Structure of Relictual Littoral and Swamp Forests in the Island of Tahiti (French Polynesia, South Pacific).

Littoral and swamp forests are among the most threatened native plant communities in the island of Tahiti (South Pacific) due to past and present anthropogenic pressures such as agriculture, urbanization, pollutions, and invasive alien species, including the mangrove tree Rhizophora stylosa. In order to provide reference data that are crucial to implement appropriate conservation and restoration strategies in these habitats, we assessed the composition and structure of seven littoral and swamp forests types in eighteen 10 × 20 m plots considering three different strata (trees and lianas, epiphytes, and understory). Forest types were compared using common diversity indices (e.g. Shannon index, Simpson index, and Pielou evenness) and indicator values. Results show that native submangrove swamp forests dominated by the tree Talipariti tiliaceum and the large erect fern Acrostichum aureum were the most species-rich, while introduced Rhizophora mangroves had an almost monospecific composition in the trees, lianas, and understory strata. The diversity of trees and lianas was higher in littoral forests with the highest understory cover in Talipariti-Barringtonia asiatica and Talipariti-Inocarpus fagifer plant communities. Surprisingly, epiphyte diversity and abundance were higher in swamp forests with lower canopy, especially in the mixed swamp forest with both A. aureum and R. stylosa. These counter-intuitive results highlight the potential role of introduced species in creating novel microhabitats suitable for the development of some native epiphytes. Conservation and restoration projects should however focus on the use of native species to maintain these remnant littoral and swamp habitats in Tahiti and other high volcanic islands of the Society archipelago, rather than nonnative and potentially harmful species such as R. stylosa. [ABSTRACT FROM AUTHOR]