OBJECTIVES

1) To assess the efficacy and ecological impacts of alternative management practices to be used for regeneration of koa forests on degraded landscapes.

2) To conduct benefit-cost analyses for individual management practices used in koa reforestation.

3) To provide land managers with practical management strategies for successful koa regeneration and kikuyu grass suppression.

APPROACH

Objective 1. The experimental sites will be located within Humuula/Hakalau on the eastern slope of Mauna Kea, on the island of Hawaii. A 2x2 factorial treatment design will measure the effects of grass-selective herbicide and fertilizer applications on kikuyu grass suppression and koa regeneration. Three of the replications will be established in the scarified region, and another three replications will be established in the non-scarified region. Thus, this experiment will have a total of 24 treatment plots. The suppression of kikuyu grass will be measured as responses to the herbicide and fertilizer treatment combinations. Percent cover of the kikuyu grass for each treatment plot will be determined using computer-assisted digital image analysis. Nutrient levels of juvenile leaf pinnules and mature phyllodes will be measured to estimate nutrient uptake and leaf nutrient-use efficiencies. Ten randomly selected koa plants from each treatment plot will be sampled from the third most apical branch. Tissue samples will be collected every six months and submitted to the Agricultural Diagnostic Service Center, University of Hawaii for complete nutritional analyses. Bradyrhizobium densities in the soil will be measured using the most probable number (MPN) plant infection technique. Sample populations of bradyrhizobia will be isolated for genetic diversity analyses using polymerase chain reaction (PCR) strategies.

Objective 2. In this objective, we will predict commercial potential of long-term koa production in response to the treatments applied during the early stages of regeneration from the experiments in objective 1. We will estimate the current wood volume of the regenerated 20-year Hakalau stand by measuring tree density, forking heights and diameters. With this information, along with data collected during the first three years from the control plots, we will develop a linear equation that describes the first twenty years of growth of a koa stand, which receives no herbicide and fertilizer. Our most conservative estimate will be that after 20 years, the growth of koa will have reached a maximum and for the next 10-15 years, development is focused only on the conversion of sapwood into heartwood.

Objective 3. A field day will take place at the Humuula and Hakalau sites, in the third year of this project. Six months prior to the event, we will be actively inviting pertinent stakeholders to attend. An extension bulletin will be published in collaboration with the Publication and Information Office, College of Tropical Agriculture and Human Resources (CTAHR). This bulletin will be made available to the public, free of charge. The format of the bulletin will be a manual with discrete instructions written in a non- technical language that can be understood by the layperson. A 30-min extension video will be produced in collaboration with the Publication and Information Office, CTAHR. The production of this video will be in a style that is suitable for public access television. The contents of this video will include several aspects of koa production in Hawaii, with a primary focus on koa regeneration.

Two field experiments were established in rangelands located on Mauna Kea in September of 2005. These experiments were established as complete factorial designs to test the interactions of herbicide and fertilizer for controlling the dominant weed kikuyu grass (Pennisetum clandestinum). Kikuyu grass is the dominant vegetation of this landscape and has not been grazed for more than 3 years. Thus, creating a habitat that inhibits natural regeneration of koa (Acacia koa) forest from the soil seed bank. Current densities of this mature sward have been measured at 1500 kg per hectare. In this research, the kikuyu grass is designated into three major fractions of the above ground biomass. These include foliage (photosynthesizing tissues), stolons, and thatch (dead accumulations derived from decomposing foliage and stolons). The foliage only accounts for 10% of the total biomass, while stolon and thatch fractions make up over 40% of the total biomass each. Early in these experiments, it is clear that the herbicide applications have had a more significant effect on the grass than the fertilizer applications. Four months after the first treatment applications (4 MAT), the herbicide plots showed a significant decrease in foliage and corresponding increase in thatch. Interestingly, there were no significant differences for stolon and total weight. In May (8 MAT) however, the herbicide-treated plots showed a significant reduction for all categories. The nutritional status of the vegetation and soil is also being monitored in these experiments. Again, the herbicide treatments have created the most significant effects. Herbicide treatments have resulted in thatch compositions with lower C:N ratios. Herbicide treatments have also resulted in significantly lower N, P, and K concentrations for the foliage and stolon fractions. Soil P concentrations were significantly higher for herbicide-treated plots, while K and ammonium concentrations were significantly higher for fertilized plots. We will start in situ N mineralization experiments in September. Community DNA has been extracted from soil samples for each plot and has been amplified with primers specific to ammonium oxidizing (AOB) and nitrate reducing (NRB) bacteria. Cloning techniques will be used for identifying diversity within the AOB and NRB communities. Real-time PCR will also be employed with the community DNA to determine representation of AOB and NRB relative to the total bacterial community. Investments have been made for a high-definition video production system, which include hi-def camera, audio equipment, and an advanced video-editing computer with the latest software. To date we have filmed over 1 hour of footage and will begin the editing process this month. We expect to have our first informational video made available to the public via the CTAHR web page within this next year.

The outcome of this project will enhance koa production in Hawaii. The goals of this project are to develop and promote practical strategies for converting degraded landscape into productive koa forests. This project has already generated evidence to support safe use of these resources as a viable strategy for koa regeneration. We have developed new collaborative relationships with four other scientists in CTAHR, UH Hilo, and HARC, which has resulted in a new submission of a SARE preproposal. Our first publication should also be drafted within this next year.

PUBLICATIONS (not previously reported): 2005/08 TO 2006/08

Leary, J., Scowcroft, P., Singleton, P. and Borthakur, D. 2006. Symbiotic diversity of the cosmopolitan genus Acacia. Symbiosis. 41: (in press)