Variation in Germination Traits Inform Conservation Planning of Hawaiʻi's Foundational ʻŌhiʻa Trees

ABSTRACT

Climate can play a critical role in seed development and germination. Linking seed germination information with environmental variables and provenance may be important in understanding plant community structure and response to climate change, which can help guide conservation planning. Native Hawaiian Metrosideros (Myrtaceae; ʻŌhiʻa) is a hyperdiverse species complex that dominates Hawaiʻi's wet and mesic forests and serves as the most bioculturally important native plant in Hawaiʻi. In response to Rapid ʻŌhiʻa Death, a major threat to native forests caused by introduced fungal pathogens, seed collections of ʻŌhiʻa across the state have increased. We used initial seed germination data from recent collections stored in the National Tropical Botanical Garden’s Seed Bank to explore if seed germinability is correlated with seed zones and environmental variables. Linear models of the proportion of seed germinated, seed zones, and environmental data revealed that only seed zones were significantly correlated with the proportion germinated. Seed germination was lower for the “Nā Pali Valleys” than the “Windward Ranges.” Generalized provisional seed zones are a helpful tool for conservation collecting and restoration planning. Germination data routinely collected for seed bank collections provide an easily accessible source of preliminary information for these purposes.

KEYWORDS:

• collections
• conservation planning
• Hawaii
• Kauai
• Metrosideros polymorpha var. glaberrima
• ohia
• seed germination
• seed zones

Acknowledgments

The authors thank Brenna Fowler, Mike DeMotta, Uma Nagendra, Natalia Tangalin, Randy Umetsu, and Ken Wood, for help with collecting ʻŌhiʻa seeds as part of this specific collection effort. The authors thank the Hawaiʻi State Department of Land and Natural Resources, Division of Forestry and Wildlife and State Parks and private landowners for site access and permission to collect (I2615 and K2020-5008cc). The authors thank Margaret Clark, Kelli Jones, Jeffrey Frelinger, Leslie Ridpath, and the students, interns, and volunteers who have helped conduct the germination studies from which the data used in the present study was obtained. The authors also thank Ben Nyberg and Adam Williams for access to the unpublished seed zone data. The authors thank two anonymous reviewers whose comments improved the manuscript.

Disclosure statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Author Contributions

DW, SW and NR conceptualized the study. DW designed and conducted the original germination studies. DW designed and conducted the statistical analysis with input from CJB. ES advised on the structure of the manuscript and the interpretation and discussion of the environmental correlation data. DW, SW and NR wrote the manuscript. All authors reviewed and edited the manuscript and approved the final version.

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website

Data Availability Statement

The data that support the findings of this study are included as supplementary material online. Table S1. Materials and methods used in seed germination study, PTBG corresponding herbarium voucher specimen barcode (https://ntbg.org/database/herbarium) and proportion germinated.

Table S2. Calculated values for 19 bioclimatic variables at each collection site.

Funding

The authors thank the Hawaiʻi Tourism Authority (CON 18117) for funding to collect ʻŌhiʻa seeds on Kauaʻi for ex situ conservation. The development of the idea for this research was supported by an International Network Grant from the Ministry of Higher Education and Science, Denmark to NR (#9096-00049B).