USDA Forest Service

Pacific Southwest Research Station

Pacific Southwest
Research Station

1731 Research Park Dr.
Davis, CA 95618
(530) 759-1700
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics

Ecosystem Processes: Tropical Ecosystems

Invasive Species in Hawaii

The mission of the Invasive Species Team is to provide new information on the ecology of invasive plant species; their impacts on the health, management and restoration of native forested ecosystems of Hawaii and the Pacific Islands; and ways in which their populations might be limited by development of biological control agents and effective land management.

Alien invasive plants threaten the unique biota of Pacific islands, the productivity of their managed forests, and our ability to restore degraded landscapes. The Institute has been an important partner with public and private sectors in weed research and management programs since 1983. Our research and outreach efforts focus on three general areas:

  1. research on the effects of important invasive plant species on native and restored Hawaiian ecosystems;
  2. research to increase the effectiveness of insects used as biological control agents on invasive weeds;
  3. development and dissemination of information on alien and invasive species of Hawaii and the Pacific Islands.
Hawaii Volcanoes National Park Quarantine Facility

Successful biological control of weeds depends upon a network of international cooperators, sustained funding of projects for up to 10 years or more, and the commitment of trained personnel and specialized quarantine facilities. The Institute of Pacific Islands Forestry operates the Hawai'i Volcanoes National Park Quarantine Facility, one of only two USDA-APHIS-certified insect containment laboratories for biocontrol in the state. Our ability to develop safe, effective agents is strengthened by partnerships with the National Park Service, US Geological Survey--Biological Resources Division, University of Hawai'i, Hawai'i Department of Agriculture, Hawai'i Division of Forestry and Wildlife, the US Fish and Wildlife Service, and the Hawai'i Invasive Species Council. We also collaborate with researchers outside Hawai'i, including scientists working where our target weeds are native.

Strawberry guava or waiawi

(Psidium cattleianum, Myrtaceae) infests thousands of acres of native rain forest. Its dense thickets suppress native species, provide a major food source to fruitfly pests of Hawaiian agriculture and cost taxpayers and landowners millions of dollars in damage and control expenditures annually. We have studied Tectococcus ovatus (Homoptera), a scale insect from Brazil that creates galls on young leaves. Our quarantine testing in Hawai'i and observations in Brazil demonstrate that T. ovatus is highly host specific, attacking strawberry guava, but not its relative, common guava, or other members of the family Myrtaceae in Hawai'i. In studies this insect reduced fruit production, which could slow the spread of strawberry guava.

Research Projects

[Photo]:Falcataria moluccana forestAn assessment of the impact of Falcataria moluccana, an N-fixing tree, on lowland wet Hawaiian forests. F. Hughes, J. Denslow, S. Cordell. Falcataria changes many aspects of the nutrient dynamics of these forests, including phosphorus and nitrogen supply, decomposition rates, and uptake. These changes facilitate the loss of the native dominant, Metrosideros, and the invasion of other exotics.

Weed Risk Assessment. J. Denslow, C. Daehler (U. Hawaii). We adapted a program developed in Australia and New Zealand for use on Pacific high islands and evaluated its predictions against expert opinions of species in the horticultural trade. The system identifies pest and non-pest species with about 87% accuracy. It is now being used in Hawaii to avoid use of potentially invasive species in the nursery and horticultural trade. Read about it in the attached pdf or visit the Hawaii Pacific Weed Risk Assessment web site for information on individual species.

Don't Plant a Pest
Weed Risk Assessments for Hawaii and Pacific Islands

[Photo]: Kona-Hema preserve Impediments to understory development in mesic tropical forest. J. Denslow, A. Uowolo, F. Hughes. This experiment at the TNC Kona-Hema preserve evaluates the effects of seed rain, exotic grass cover, canopy cover and elevation on the development of understory vegetation in sites proposed for koa management.

Survey of Invasive Exotic Plant Species in Conservation Areas on Oahu, Hawaii. J. Denslow. We interviewed land managers responsible for 42 different management units covering a total of 31,400 ha and ranging in size between 0.5 ha to over 9800 ha. Of the 497 species recorded, 277 were abundant on one or more sites, 211 species were seen to cause ecological damage due to competitive effects on native species or to alteration in ecosystem processes, and land managers report that they were actively controlling 173 species. A summary report is available as the attached pdf. Contact J. Denslow for a copy of the database.
Oahu Weed Survey Project Report

[Photo]: R. Nagata monitoring traps Use of pheromone traps to monitor biological control agents on Rubus spp. T. Johnson, R. Nagata. We are working with HortResearch, NZ to develop pheromone traps to monitor populations of biological control agents more effectively.

[Photo]: Plants in pots Growth responses of native and invasive plants to light and nutrients. J. Denslow, A. Uowolo. Growth patterns and habitat requirements of native species are compared to those of invasive pest plants of similar growth form in a shade house experiment.

Pacific Island Ecosystems at Risk (PIER). J. Space has completed reports on invasive species of environmental concern for American Samoa, Federated States of Micronesia, Northern Marianas, Guam, Palau, Niue, Samoa and Tonga. Summaries of species found, their characteristics, and distributions can be found here.

[thumbnail] link to ipif_biocontrol03.pdf
Research Updates:

PDF A Potential New Tool for Managing Strawberry Guava

[thumbnail]: Link to ipif_Don'tPlantPest04.pdf
In Brief:

PDF Don't Plant a Pest: Assessing the Risk of Exotic Plants
Learn about the Hawai'i-Pacific Weed Risk Assessment System, a useful tool for selecting noninvasive plants for Hawai'i's gardens and landscapes.

Research conducted by: