Seedlings of a native shrub can establish under forests dominated by an alien tree, Casuarina equisetifolia, on subtropical oceanic islands

Abstract

We investigated the effects of litter accumulation by an alien tree, Casuarina equisetifolia, on the germination and seedling establishment of Rhaphiolepis wrightiana, a shrub native to the Ogasawara (Bonin) Islands, in the northwestern Pacific Ocean, in a field experiment. We compared the emergence of seedlings in forests dominated by C. equisetifolia with that in native forests, with and without litter removal. More than 75% of seedlings emerged during a year except at the C. equisetifolia sites with litter removal (approximately 45%). Thus, seeds of R. wrightiana can germinate under C. equisetifolia if they are dispersed on the ground.

Keywords:

• Field experiment
• Invasive species
• Litter accumulation
• Ogasawara (Bonin) Islands
• Rhaphiolepis wrightiana

Acknowledgments

The Environmental Agency and the Department of National Forests in the Ogasawara Islands allowed us to conduct this study on Chichijima. This study was financially supported in part by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science, the Fund for Global Environmental Research of the Ministry of the Environment of Japan (Grant No. F-51), and a Grant-in-Aid for Scientific Research (A) No. 22241055. We thank the Department of National Forests in the Ogasawara Islands and the Ogasawara Subtropical Agriculture Center for providing locations for the field experiment.