Vascular plant species of the Kingdom of Tonga by vegetation type, species origin, growth form, and dispersal mechanism

Abstract

The aim of this research is to compile a database of vascular plants found in the Kingdom of Tonga in western Polynesia, a phyto-geographic subregion of the South Pacific. The Tongan islands are spread over ~600,000 km2 of the Pacific Ocean between 15–23° S latitude and 173–177° W longitude. The archipelago is comprised of 171 islands with an aggregate land area of about 720 km2. Since there is no comprehensive or updated flora for Tonga, we use 143 published sources to compile a database for 1,020 plant species, of which more than 450 are indigenous to these islands. Tonga is noteworthy for its low proportion of endemics, accounting for <5% of the indigenous species and <2% of the total plant species. Our database documents species presence in Tonga as a whole, and more specifically on 11 Tongan islands or island groups. We have assembled ecological information for each plant species according to growth form, vegetation type, origin (endemic, indigenous, and introduced species), and dispersal mechanisms. We include introduced species in our database because they represent over half of the plant species growing in Tonga. Species origins reflect human alteration of Tongan ecosystems in which endemic and indigenous species represent pre-human vegetation and introduced species indicate plants brought by either Polynesian or European settlers. For example, on Tongatapu, the largest and longest occupied island, more than half the plants are introduced, whereas on the sparsely populated, more remote islands, 70–90% of the species are indigenous. Dispersal mechanisms, which may include more than one mechanism per species, are documented in over 100 publications. Our database provides information on the whole suite of plant dispersal mechanisms over entire communities or island groups in Tonga. Plant species dispersal differs across environmental variables, including island geology, topography, vegetation type, and species origin. The older limestone islands have more bird, water, and human-dispersed plants, while the youngest volcanic islands have the most wind-dispersed species. Our database documents plant species endemism, introductions, vegetation types and dispersal mechanisms that reveal key biogeographic dynamics of the Tongan archipelago in the South Pacific. Please cite this Ecology Data Paper if the data are used in publication, presentation, or teaching activities. There are no copyright restrictions.