Regaining habitats from invasive weeds by planting limited-recruitment endemic trees on an oceanic island: successes and failures 11 years later

The degradation of biodiversity caused by anthropic habitat destruction is a global issue. The recovery of natural habitats from invasive alien weeds in order to conserve endemic ecosystems is especially important on small oceanic islands. Planting of endemic trees may be an effective measure, but a complete restoration process within the island is essential to avoid accidental introduction of invasive aliens. To test planting techniques, we planted two endemic tree species whose regeneration was hindered by alien species on degraded lands on Chichi-jima (Ogasawara Islands) and monitored vegetation changes. During an 11-year period, about half of the Elaeocarpus photiniifolius seedlings survived in gap areas, but all Morus boninensis failed. The E. photiniifolius trees reached a height of 4.7 +/- A 2.4 m. The restored canopy created a dark environment that greatly reduced the volume of the predominant invasive weeds. These results suggest that E. photiniifolius is suitable for restoration of forests on degraded land and for the suppression of weeds on the island. Low species diversity in the restored forests, however, was a remaining issue to be addressed. Herein we discuss potential improvement measures to facilitate the recovery of species diversity, including other native tree candidates.