OBJECTIVES

Goal:
1) Evaluate the effectiveness of a native plant agroforestry system in suppressing invasive weeds as a part of invasive species control and forest restoration.
2) Manage this system for the purpose of:
A) promoting native plant restoration and biodiversity conservation;
B) enriching the culture of Native Hawaiians; and
C) providing viable economic returns.

Objectives:
1) Measure productivity of and harvestable yield of planted native agroforestry species.
2) Evaluate plant nutritional status and the effects of native agroforestry species on nutrient cycling processes.
3) Monitor the effects of the native agroforestry system on the site microenvironment.
4) Determine the response of native and invasive plants to the implementation and management of the native agroforestry system.
5) Calculate the economic costs and benefits of the agroforestry system.

APPROACH

The utilization of native plants with economic potential and cultural significance within a system designed to suppress understorey invasive weeds essentially describes a multipurpose agroforestry system. Thus, it bridges the gap between the fields of agricultural management, forest and plant ecology, biodiversity conservation, and cultural enrichment. This approach can help guide meaningful and productive research to ensure the proper design and management of appropriate agroforestry systems in order to achieve these multiple goals. The goal of the research outlined in this proposal is to establish and evaluate the potential of an initial single agroforestry design to provide these multiple benefits. This project will take place within a degraded and reforested watershed on the island of Oahu. The understorey is dominated by alien, invasive plants. The overstorey was removed during the 1800's and partially restored with plantings of alien species during the early 1900's. Above the replanting zone is a degraded forest with scattered remnants of native trees. We will establish our agroforestry system in both the degraded and reforested zones by clearing the understorey and planting 3 common native species that are ecologically, culturally, and economically important to Hawaii. The selection of species and the planting design is intended to complement the structural architecture of the species, while optimizing the trade-off between target plant productivity and weed suppression effectiveness. We will evaluate the ability of this system to achieve its multiple objectives. Plant productivity will be measured by destructive harvests and allometric relationships to non-destructive measurements. Plant nutrition and nutrient cycling will be studied by direct analysis of plant tissues and monitoring of litter deposition and decomposition rates. Microenvironmental measurements will include soil water, air temperature and RH and light levels (PAR). The response of the vegetative community will be determined through seedbank germination trials and monitoring of seedlings actually regenerating in the field, both native and alien. Finally, we will evaluate the economic viability by calculating establishment and maintenance costs vs. potential returns from harvestable plant material and reductions in weed control costs.

PROGRESS

2005/10 TO 2006/09

This goal of this project is to develop a productive native plant agroforestry system in the forest understory as a means to restore native ecosystem biodiversity and suppress the reestablishment and spread of invasive plant species. During the past year, native plant species (Pipturus albidus, Microlepia strigosa, and Alyxia oliviformis) have been established and monitored for growth in cleared and uncleared forest plots with and without a planted forest overstory. Results show that native plants will only thrive in plots cleared of the invasive understory species, Ardisia elliptica. Second, the invasive species itself does not persist in the seed bank; thus, replanting is an effective mechanism for replacing the invasive species. Third, as expected, native plants in plots without a planted overstory grow better than underneath non-native forest canopy cover. However, greater solar radiation and soil temperatures lead to greater soil evaporation and lower soil water availability in plots without a planted overstory. Growth of the native fern, Microlepis strigosa, has been particularly good. It is conceivable that there will be sufficient harvestable biomass over the next year's growth. The native planted shrub, Pipturus albidus, has already become a host for the larvae of the native Kamehameha butterfly, but this herbivory has not endangered the survival of the plants.

IMPACT 2005/10 TO 2006/09 This project is expected to provide a viable strategy for jointly suppressing invasive species and restoring native plants by incorporating them into an agroforestry system. Early growth of the native fern is promising for both suppressive and economic uses. Correlation of plant growth with site variables like understory light levels and soil moisture and temperature will provide valuable guidelines for predicting the success of replanting efforts. The presence of native butterfly larvae suggest even small areas of restored native plant communities can increase native faunal biodiversity, as well.

PUBLICATIONS (not previously reported):
2005/10 TO 2006/09

Nazario-Leary, C., Idol, T., and Ticktin, T. Development of a Native Plant Agroforestry System to Control Invasive Species and Promote Forest Restoration in Hawaii. 2006 Hawaii Conservation Conference.