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.

Mapping habitat suitability for at‐risk plant species and its implications for restoration and reintroduction

“…Over 40% of all at-risk plant species occur in dry or rocky habitats where low water availability is a barrier to recovery (Kew Royal Botanic Gardens 2010), including the highly endangered dry-lands where we work in Hawaii (Dobson et al 1997). Reintroduction programs have had limited success in many drylands due to a low probability of establishment and high levels of plant mortality (e.g., Cordell et al 2008). Often planting areas are arbitrarily or opportunistically selected without consideration of microclimatic gradients.…”

Future directions for forest restoration in Hawai‘i

“…Nutrient loading [i.e., applying fertilizers past the point of increased growth to where the seedlings take up excess nutrients (luxury consumption)] has also been shown to increase N concentration in Acacia koa seedlings (Dumroese et al 2009), which should help them to establish well in N-poor grasslands. Cordell et al (2008) found that vines had twice the survival rate of tree seedlings in an extremely dry site and recommended these for initial planting on disturbed sites. Coordination with field crews regarding timing of planting is critical, as trees can be vulnerable to frost at high elevation sites during winter months (Scowcroft and Jeffrey 1999), and managers need to be able to plant dry sites during the wettest part of the year.…”

Broadcast Seeding as a Potential Tool to Reestablish Native Species in Degraded Dry Forest Ecosystems in Hawaii

“…Another Hawaiian dry forest study observed an outplanting tree seedling survival rate of 34%, but that effort was more labor intensive, since the seedlings received supplemental watering for six months (Cordell et al 2008). Comparing costs and results of planting seedlings verses broadcast seeding in this environment may be a needed direction for future research.…”