Contact
Dr. J. B. Friday (jbfriday@hawaii.edu)
Phone: 808-981-5199
Fax: 808-981-5211

FUNDING has been provided to CTAHR for this research from the USDA Cooperative State Research, Education, and Extension Service Project HAW00126-06G.

OBJECTIVES

The goal for our research is to develop a rigorous understanding of the productivity of the native Hawaiian hardwood koa (Acacia koa) and to develop the silvicultural tools landowners need to effectively manage regenerating koa forests. Our experimental objective is to assess koa response to thinning, fertilization, and weed control in young stands of three different ages and three different densities. Our second objective is to develop a simulation model of koa productivity based on mechanistic relationships and field data from this and other experiments. Lastly, we plan to develop practical silvicultural guidelines based on the knowledge gained from the field studies and models.

APPROACH

We will install experiments at three sites on the Big Island of Hawaii to investigate responses to thinning, fertilization, and grass control in dense young stands of Acacia koa. The first site, Honomalino, is relatively dry (1000 mm precipitation) with thin soils. The second site, Keauhou Ranch, is wetter (2500 mm precipitation), also with thin soils. The third site, Umikoa ranch, receives 2500-3000 mm precipitation and is on deep soils. Grass control will be controlled with a grass-specific herbicide. Triple super phosphate will be applied biannually at a rate of 15 g/m2 to the fertilized plots.

1. Aboveground Productivity
A. We will measure dbh annually in all plots in order to estimate koa productivity under normal site conditions and as altered by the silvicultural treatments.
B. We will measure crown area and depth and the vigor class of selected trees and calculate the live crown ratio.
C. We will monitor specific leaf area in all the stands.
D. We will use determine water use efficiency from leaf C stable isotope ratios.
E. We will excise branchlets in the upper canopy of select koa and measure instantaneous photosynthesis. Measured leaves will be brought back to the lab for analysis of SLA, N and P concentration, and C isotope ratio.

2. Soil Nutrient Supply:
We will use ion exchange resin membranes embedded in plastic stakes, known as PRS-probes, to measure soil nutrient supply at all locations.

3. Environmental Monitoring:
We will monitor air temperature and relative humidity, photosynthetically active radiation (PAR), precipitation, soil temperature, and soil water content at all three locations.

4. Growth and Stand Development Modeling

A. We will combine the growth data from our study with data collected at other Hawaii long-term growth plots to develop site index curves for koa. We will use this data in the simulation model developed by Grace (1995) to develop a more comprehensive assessment of koa growth and productivity.

B. We will use the physiological and ecological data obtained to develop a koa-specific version of the forest growth and development model 3PG.

5. Development of Silvicultural Recommendations for Koa Management:

A. We will use the 3PG simulation model to provide forest managers an estimate of potential koa productivity on specific sites and under various silvicultural treatments. The 3PG model will be used to develop site-specific silvicultural recommendations, including thinning guidelines, grass control, and fertilization needs.

B. We will combine koa growth rates with data on management to conduct a cost-benefit analysis of koa forestry on various sites. This will be used to provide managers a financial analysis for various koa management scenarios across a range of site conditions.