Travis Idol, Department of Natural Resources and Environmental Management, UH-CTAHR
J. B. Friday, Department of Natural Resources and Environmental Management, UH-CTAHR
Paul Scowcroft, Institute of Pacific Islands Forstry, USDA Forest Service
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Acacia koa is a highly valuable timber tree that grows across a wide range of climatic conditions and soil age in Hawaii. There is some knowledge of its productivity across this range, but there is little knowledge of what silvicultural treatments - thinning, fertilizing, etc. - are best to improve productivity and meet landowner objectives. This project will address the need for site-specific productivity data and silvicultural recommendations for Acacia koa forests.
Contact
Dr. Travis Idol (idol@hawaii.edu)
Phone: 808-956-7508
Fax: 808-956-6539
FUNDING has been provided to CTAHR for this research from the USDA Cooperative State Research, Education, and Extension Service Project HAW00114-M.
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OBJECTIVES
1) To develop a mechanistic understanding of the influence of soil water and nutrients on koa production and stand development through comparison of koa stands across natural environmental gradients.
2) To determine the response of koa productivity and resource use in response to silvicultural manipulations of resource availability.
3) To create a robust model that predicts koa production and development across its natural range and in response to management.
4) To develop guidelines for practical management of naturally regenerated, even-aged koa stands based on this improved understanding of spacing, water, and nutrient requirements.
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APPROACH
We will utilize silvicultural treatments and natural stand dynamics to address potential limitations to Acacia koa productivity at sites that differ in soil fertility and climate. Thinning, grass control, and P fertilization will be used at two locations: one represents a mesic site on young, less fertile soil; the other represents a wet site on older, more fertile soil. A third site, located at a mesic site on a very old, infertile soil will be used for comparison, but no silvicultural treatments will be imposed. Measurements will include: basal area increment, soil phosphorus supply, soil water availability, and nutrient cycling pools and processes. These measurements will be used to modify the forest growth and development model 3PG for A. koa in Hawaii across its natural ecological range. This calibrated model will be used to simulate the effects of specific silvicultural options across a range of sites. The outcome of these simulations will be combined with information gained from field work to develop site-specific silvicultural recommendations and growth and yield predictions.
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PROGRESS
2005/10 TO 2006/09
The objective of this project is to use field-based measurements of koa site productivity relationships plus experimental implementation of silvicultural practices to develop effective silvicultural guidelines for Acacia koa. During the past year, we have initiated this project and made progress in the following areas: Site selection: In addition to the established silvicultural treatments on a young soil with high rainfall, we have established plots in the following locations 1) Laupahoehoe: a high rainfall site on older, deeper ash soils at relatively low elevation on Mauna Kea soils. This site represents the maximum productivity for koa in most naturally-regenerated stands. 2) Kokee: a moderate rainfall site on highly, weathered soil at relatively low elevation on Kauai. This site represents the oldest and theoretically most nutrient-poor site, especially for P. Productivity is most likely limited by nutrients. 3) Umikoa: a high rainfall site on older, deeper ash soils at relatively high elevation on Mauna Kea soils. This site will be used for expermimental silviculture treatments and is most comparable to Laupahoehoe. 4) Papa: a low rainfall site on young, thinner ash soils at a moderate elevaiton on Mauna Loa soils. This represents the lowest productivity site due to thinner soils and lower precipitation. This site will be used for silvicultural treatments. The soil age is comparable to established plots at Keauhou Ranch, but rainfall is much lower. Stand inventory/productivity: We have determined stem diameter on representative plots at all locations. Stand basal area differs, as expected. Productivity as estimated by basal area increment will be determined from follow-up inventory measurements. Soil Nutrient availability: Resin-membrane stakes have been put in place at Laupahoehoe and Kauai and are being compared to data from Keauhou Ranch. As expected, P availability is highest at Laupahoehoe and lowest at Kokee. Soil P fractionation: Soil P exists in various biogeochemical fractions that differ in their availability to plants and biological activity. Differences among sites gives information on inherent soil P supply capacity. Differences with silvicultural treatments, especially P fertilization, give vital information on the ability of the ecosystem to maintain active cycling of added P and thus maintain increased growth rates.
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IMPACT
2005/10 TO 2006/09
This data should provide necessary information to develop site-specific silvicultural recommendations as well as general predictions of site productivity and stand response to silvicultural treatments. This will allow foresters to optimize productivity and net returns from active management, as well as improve site conditions for regeneration of other native species.
PUBLICATIONS (not previously reported): 2005/10 TO 2006/09
Scowcroft, P.G., Friday, J. B., Idol, T.W., Dudley, N., Haraguchi, J., and Meason, D. Targeted silviculture improves koa (Acacia koa) tree growth. 2006 Hawaii Conservation Conference.
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