Management implications for the reintroduction of the endangered Hawaiian state flowerHibiscus brackenridgei

Abstract

Dry forests of Hawai'i are one of the most endangered forest types worldwide with 45% of all native tree and shrub species listed as federally threatened or endangered. Supplementation and reintroduction of endangered dry forest species are necessary to maintain viable population sizes. The goal of this research was to reintroduce Hibiscus brackenridgei mokuleianus, the state flower of Hawai'i and a federally endangered species, into its historical range on O'ahu. We determined the environmental variables contributing to plant survival and growth, assessed the effectiveness of a reintroduction program with minimal management, and evaluated the potential for habitat suitability models to assist in selection of optimal sites for reintroduction. Forty‐five individuals were grown from cuttings and transplanted in two regions: Ka'ena Point (2 sites, 10 individuals each site) and along Kealia Trail (5 sites, 5 individuals each site). Survival and height measurements were taken four times over the course of 25 months. There was 35% survival at Ka'ena Point and 76% survival at Kealia Trail and an average plant growth of 70.5 cm (±30.1 cm) and 121.6 cm (±61.7 cm), respectively. Ka'ena Point had significantly lower survival (p > 0.001) and growth rates (p > 0.001) than Kealia Trail. Plants survived best at sites with steep slopes and high soil moisture and grew the most in sites with steeper slopes, higher soil moisture, and lower soil bulk density. These findings provide insight into environmental variables which should be considered prior to planting as well as the intensity of site management.