Tree diversity, vegetation structure and management of mangrove systems on Viti Levu, Fiji Islands

Abstract

Mangrove forest ecosystems are critical natural resources, particularly in the South Pacific region. Mangrove forests in Viti Levu, Fiji’s main island, are threatened by infrastructure development activities and population growth. Consequently, the protection and restoration of mangrove forest are of utmost importance. This study investigated the diversity and structure of mangrove forest on Viti Levu to determine the most appropriate species for use in restoration projects. These species could enhance the management of mangroves in Fiji. Five sites were selected: Ellington Wharf (EW), Naboutini Village (NV), Nasese (NA), Suva City Council Park (SCCP) and the University of the South Pacific Upper Campus (UUC). The variations in the number of tree stumps from site-to-site highlighted differences in the degree of anthropogenic disturbances, EW was classified as an undisturbed site while NA was highly disturbed. The sites were examined using systematic line transects with random starting points. Continuous belt transects were established, along which 10 m × 10 m segments were selected as the primary plots (n = 100 primary plots). Tree species, stand structure, tree diameter and height, stem abundance, stand volume, basal area and natural regeneration were recorded at all sites. Five mangrove species (Rhizophora stylosa Griff., Bruguiera gymnorhiza (L.) Lam., Excoecaria agallocha (L.), Rhizophora samoensis (Hochr.) Salvoza, and Rhizophora × selala (Salvoza) Toml.) were identified. The species importance value indices were highest for R. stylosa at EW (264.0) and for B. gymnorhiza) at NV (175.2). All sites had at least some level of human disturbance but R. stylosa and B. gymnorhiza thrived regardless of the extent of anthropogenic impacts. Subsequently, R. stylosa and B. gymnorhiza are recommended for mangrove forest ecosystem restoration programmes in Fiji.