Short-term recovery of native vegetation and threatened species after restoration of a remnant forest in a small oceanic island of the South Pacific

Background: Invasive alien species have transformed many natural ecosystems, especially on islands where endemic species are critically endangered, and where habitat restoration is a challenge. Aims: We set up an experimental protocol to aid the restoration of a native remnant forest by excluding feral ungulates and suppressing an invasive tree. Methods: Sixteen plots of 144 m(2) were delimited in a dry-mesic forest located on the small oceanic island of Rapa Iti (South Pacific) and half of them were fenced. The invasive tree Psidium cattleianum was manually cut in four fenced and four unfenced plots. We monitored understorey species diversity and abundance every 6 months for a period of 30 months in twenty-four 4-m(2) quadrats randomly selected in each plot. Results: A significant increase of native species richness occurred in the fenced plots where the invasive tree was suppressed, and a decrease of alien species diversity in the fenced plots. The abundance of native and alien species was significantly reduced in the fenced plots, where recruitment of endemic threatened species was observed. Conclusion: Rapid vegetation change occurred in 30 months. The understorey plant community response to ungulate exclusion and invasive tree removal strongly differed between native and alien species, with the recovery of native vegetation.