Towards restoration of Hawaiian tropical dry forests: the Kaupulehu outplanting programme

Abstract

Hawaiian tropical dry forests contain diverse assemblages of woody canopy species, including many endemic and endangered species that warrant conservation attention before completely disappearing. Today, tropical dry forests in Hawaii are not viable ecosystems. Poor land use practices, fragmentation, non-native plant invasions, and inadequate native vegetation regeneration are all factors that have contributed to their endangerment. Only an ambitious restoration programme that includes non-native ungulate exclusion, weed control, fire management, and the outplanting of seeds and seedlings will be sufficient to enhance Hawaiian tropical dry forests. We selected a 25 ha preserve within the Kaupulehu Dry Forest Preserve, located in North Kona on the Island of Hawaii, to test dry forest restoration strategies. In 1997, the preserve was fenced and all non-native ungulates were removed. Altogether, 4892 outplants were planted from 1999?2006. In 2007, we surveyed all of the outplants. The survey found 1487 live plants, 3357 dead, and 48 plants missing. This equates to an overall survival rate of 30%. Survival by vegetation type indicated that vines had the highest rate of survival (63%) followed by trees (34%). Herbs had the lowest rate of survival (12%). Twelve of a total of 35 species that were outplanted in the Kaupulehu Dry Forest Preserve accounted for more than 90% of the total surviving plants species, while five federally listed species represent almost 60% of the total. The outplanting of dry forest species into the Kaupulehu Dry Forest Preserve considerably increased the population of many federally listed endangered species. However, the high mortality of many common and important plant species of tropical dry systems highlights the importance of an outplanting programme that emphasizes ecosystem sustainability rather that species success. In equal measure, the successes and failures of the Kaupulehu outplanting project have enhanced our ability to begin to restore this unique and endangered ecosystem.