Granting Agency: USDA, Tropical-Subtropical Agriculture
Project Period: Oct. 2004-Sep. 2008
Principal Investigator: Travis Idol
Co-PI's: Tamara Ticktin and Rainer Bussmann
Restoration of Hawaii's forests requires tremendous expenditure of man-hours and plant materials. Governments and large conservation organizations may have the resources and dedication to accomplish this. Community groups, however, rarely have the ability to do more than pull weeds and attempt to stop the spread of invasive species. Our objective is to develop sustainable agroforestry systems using native plants. The community of plants chosen are based on their historic co-occurrence in a specific life zone and their economic and cultural importance to Hawaii. The first example of this approach is in the Harold L. Lyon Arboretum in the back of Manoa Valley. For our ground cover, we chose palapalai (Microlepia strigosa), a very shade-tolerant fern that is used in hula, lei, and other cultural ceremonies. One of our shrub species is mamaki (Pipturus albida). It has a spreading upright habit, and the leaves are used as a medicinal tea. We also included in our mix the vining shrub maile (Alyxia stellata), which is used in lei but is mostly imported from other Pacific Islands. Our goal is to establish this community of native plants in a cleared forest understory so that it will not only provide a source of sustainably harvestable material but also suppress the reinvasion of shade-tolerant invasive species such as inkberry (Ardisia elliptica).
Clearing increases understory light and leads to better palapalai growth and survival of mamaki plants. As well, the photosynthetic capacity of the palapalai has acclimated to the light conditions of each particular treatment x site combination. After two years of growth, the palapalai in the cleared plots reached a harvestable size, where only 6-16% of the plant needs to be harvested to create a single lei.
Weed regeneration and biomass declined over time, indicating effective suppression and reduced need for weeding. Survival of inkberry seedlings was lowest under the most exposed conditions, but growth of the surviving seedlings was greatest. This suggests that the system is feasible for restoration agroforestry purposes.
Nazario-Leary C, Idol TW, and Ticktin T. Photosynthesis of the native Hawaiian fern Microlepia strigosa varies with overstory cover and understory clearing in an alien-dominated forest. in preparation.
We hope to expand the application of the restoration agroforestry concept to other community forest restoration projects in Hawaii and the Pacific Basin. Sites range from mostly intact native forest to forest plantations to completely cleared agricultural land. By choosing the proper mixture of species and planting them in an appropriate spatial arrangement and temporal sequence, we can enrich, restore, and recreate native plant communities and functioning ecosystems.