Demonstration of tree selection and silviculture to optimize restoration success with koa (Acacia koa)

Project Collaborators

  • Faith Inman-Narahari, Assistant Researcher, Natural Resources and Environmental Management, University of Hawaii
  • Oriana Rueda-Krauss, Project Assistant, Natural Resources and Environmental Management, University of Hawaii
  • James B. Friday, Extension Forester, Natural Resources and Environmental Management, University of Hawaii
  • James Leary, Extension Forester, Natural Resources and Environmental Management, University of Hawaii
  • Nick Koch, General Manager, Forest Solutions, Inc.

Six months after herbicide application.47 bending-over-puka
Six months after herbicide application (above), current vegetation will have decomposed; improving outcomes of site preparation by excavator and allowing newly planted koa (below) competitive advantage in a weed-free environment.

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Sites for demonstration planting near Waimea (above) and Pahala (below). These sites will be excellent for field trips for landowners from all regions of Hawaii Island.

We are developing a new extension project to demonstrate the increased growth and productivity that can be gained from planting selected koa trees using the best silvicultural practices. Currently, there are tens of thousands of acres of marginal pasture lands in Hawaii that could be reforested with koa, dramatically changing the conservation landscape. To improve planting success and to provide a compelling economic model to encouraging further planting of this important native species, we need to increase the use of seed from selected trees with desired traits and the adoption of improved silvicultural practices. We have applied for funding from a Conservation Innovation Grant from the USDA Natural Resources Conservation Service.

Using seed from selected trees delivers substantial conservation benefits. Studies on many tree species show that tree size and form are genetic traits that are passed from "mother" trees to seedling progeny. Use of selected seed for reforestation is common practice for other species, but has rarely been applied to native Hawaiian species. Today, most seeds for koa planting are collected from unselected trees, even favoring shorter trees with many low branches with easily-collectable seeds. However, recent research indicates that diameter and height growth rate are highly heritable in koa, suggesting that planting seeds from trees selected for these traits will result in faster-growing trees. Faster growth would increase the rate of success for forest restoration by decreasing the time to canopy closure and increase CO2 sequestration rates. It would also shorten economic return cycles, making forestry with this native species more attractive to private landowners.

Employing the best proven silvicultural practices is the other essential ingredient to increase restoration success and conservation gains from koa plantations. Over the past several years, koa growers and researchers have conducted numerous experiments to test and develop silvicultural practices to optimize koa planting success and growth. These experiments include trials of nursery, site preparation, and weed management practices. The best practices are proven to substantially increase growth and survival. However, many landowners remain unaware or unconvinced of the benefits of using these techniques. Additionally, much of the information is unpublished or is located in technical documents that are not easily available to landowners.

To address these issues, we propose to 1) establish accessible demonstration plantations to show landowners the dramatic improvement in koa growth and survival that can be obtained by planting seedlings from selected trees and using best silvicultural practices, and 2) consolidate the existing silvicultural information about koa into a practical user-guide and a technical note that can be used by agents in the NRCS as a major source of tree planting information used by private landowners. The treatments and concomitant messages will be simple and to the point to remain effective with a wide range of audiences. The demonstrations will serve as an educational tool to provide landowners with clear visual evidence of the utility of employing these practices; there are currently no such demonstration sites in Hawaii. We believe that by demonstrating these practices, and by making the most up-to-date information about growing koa widely available, this project will increase public acceptance and adoption of using selected seed sources and best silvicultural practices. Wider knowledge, acceptance, and adoption of these practices will lead to more successful restoration planting and higher conservation benefits of native forest.

Clear differences in growth rates between koa planted with complete weed removal versus weed removal only at planting spot. Left photo shows planting site with large seedlings in full treatment on left and small seedlings in spot treatment on right; center photo shows tall seedling with J. Leary in full treatment; right photos shows small seedling with J. Leary in spot treatment.
Clear differences in growth rates between koa planted with complete weed removal versus spot treatment. Left photo shows planting site with large seedlings in full treatment on left and small seedlings in spot treatment on right; center photo shows tall seedling with J. Leary in full treatment; right photos shows small seedling with J. Leary in spot treatment.

Cooperators

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