Establishment of early-stage planted seedlings of a native woody species under a closed canopy of invasive Casuarina equisetifolia in the subtropical oceanic Ogasawara Islands

ABSTRACT

Extirpation of invasive plants does not always result in successful restoration of native plant communities because it can alter ecosystem function or promote further incursion of other invasive plants. To test whether seedlings of native plants can become established without extirpating invasive plants, we evaluated the survival and growth of seedlings of a native tree species, Schima mertensiana, planted under closed forest dominated by an invasive species, Casuarina equisetifolia in the Ogasawara Islands, an oceanic archipelago in the western Pacific Ocean. The initial establishment of S. mertensiana is inhibited by the highly accumulated litter of C. equisetifolia; therefore, few seedlings and saplings of S. mertensiana were observed in the forest. We planted seedlings of three initial size classes, and their size parameters (diameter at ground level, height, and number of leaves) were monitored for 69 months. More than 75% of the planted seedlings survived during the study period. There were no significant differences in the number of surviving seedlings among the initial size classes. Steady growth of seedlings was observed regardless of initial size class. Our results indicate that planted S. mertensiana seedlings can survive and grow in forests without removing C. equisetifolia, and provide a case study that shows that planted seedlings of a native woody species can establish under a closed canopy dominated by an invasive woody species, at least for several years.

KEYWORDS:

• Bonin (Ogasawara) Islands
• Casuarina equisetifolia
• extirpation
• Schima mertensiana
• transplanting

Acknowledgments

The Ministry of the Environment and the Department of National Forests of the Ogasawara Islands granted permission for us to conduct this study. We thank the Ogasawara Subtropical Agriculture Center for providing the field study site and supporting the preparation of the transplanted seedlings. Anonymous reviewers and the subject editor made numerous valuable comments that improved this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.​

Additional information

Funding

This research was largely supported by the Environment Research and Technology Development Fund of the Ministry of the Environment, Japan (4-1402), and partly by JSPS KAKENHI [Grant Number 24710274].