UH-Manoa



Travis Idol's Research Page

Forestry Projects

Koa Productivity

Personnel

PI's: T.W. Idol, P.J. Baker
Student
: R. Martinez-Morales

Koa Silviculture

PI's: T.W. Idol, J.B. Friday, P. Scowcroft;
Student:
D. Meason

Forest Health Assessment

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PI's: T.W. Idol, T. Miura
Students:
C. Anderson, R. Martinez-Morales
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Agroforestry Projects

Restoration Agroforestry

Personnel

PI's: T.W. Idol; T. Ticktin, R. Bussmann
Students:
C. Nazario-Leary, T. Sherill

Shade Coffee Analysis

PI's: T.W. Idol, H.C. Bittenbender, M. Jackson
Student:
S. Steiman

Agroforestry Carbon Sequestration

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PI: T.W. Idol
Student
: A. Youkhana
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EPA P3 Constructed Wetland

PI's: T.W. Idol, C. Ferguson, L. Gautz
Students
: K. Caraway, V. de Oliveira, D. Takara, E. Mihlbauer, A. Cho, M. Saunter, B. McDowell
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Forestry Projects



Koa Productivity

Title:

Granting Agency:

Project Period:

Environmental Controls Over Acacia koa Productivity

U.S. Forest Service, Cooperative Agreement

May 2003-March 2005

Summary:

   Acacia koa is the second-most common tree in Hawaii, ranging from wet to dry-mesic forests at elevations from 500 to 6500 feet. It is also a nitrogen-fixing tree, able to overcome the inherent lack of N in young volcanic soils. Its beautiful and durable wood makes it an extremely valuable hardwood for fine furniture, musical instruments, and traditional Hawaiian canoes. It can regenerate from buried seedbanks in old pastures if exposed to light and protected from grazing. Koa restoration and reforestation projects are commencing on several of the major Hawaiian Islands. However, we do not yet know enough to model the growth and yield of koa forests across its historic range. Koa is known to be sensitive to mean annual rainfall, but no attempts have been made to relate productivity to elevation, which affects mean annual temperature. Additionally, few studies have looked at the soil and foliar nutrients in koa stands in order to determine their effect on koa productivity or their relationship to environmental variables.

   With this in mind, we established study plots at 3 locations on the Big Island of Hawaii that differed in mean annual rainfall from 1000-2000 mm. Elevation ranged from 1200-2050 m, but the extent varied by location. Soil nutrient bioavailability was measured seasonally using ion exchange resin membrane probes, known commercially as PRS-probes. Foliar nutrients were estimated for fully-expanded leaves in the upper canopy. Soil N mineralization and soil P fractions were also determined in the laboratory.

   Results showed that koa basal area increased with rainfall, as expected. Soil P also appears to play an important role. Across all sites, basal area was linearly related to the pool of exchangeable soil P. Interestingly, the soil C:N ratio declined with increasing soil P availability, suggesting that P limitations may lead to poorer quality litter production and organic matter formation. Overall, it appears that at higher rainfall rates, the greater productivity of koa stands leads to a more rapid immobilization of this limiting nutrient in woody biomass than can be replaced via P weathering from primary minerals. Scavenging for available P likely depletes the exchangeable P pool size, which is reflected in low P availability.

 

Koa basal area vs exchangeable soil P

 

Available P vs soil C:N ratio

   Combined with data from other locations, we are using this information to calibrate standard ecological models of forest growth and productivity. The interactive effects of precipitation and temperature on nutrient status and forest productivity will have to be incorporated into a modified model in order to accurately reflect the true dynamics of these systems.

Publications:

Idol TW, Baker PJ, and Meason D. 2007. Indicators of forest ecosystem productivity and nutrient status across precipitation and temperature gradients in Hawaii. Journal of Tropical Ecology 23:693-704. doi:10.1017/S0266467407004439

Future Directions:

We hope to expand the standard growth metrics taken so far with remote sensing tools such as ground-based laser detection and ranging (lidar) to estimate details of stand structure and satellite imagery to rapidly assess forest health and productivity at the landscape scale. The goal is to use this information to calibrate a forest production and stand dynamics model, such as 3PG.

Koa regeneration after scarification

Dense koa stand-dry site

PRS-probes

 

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Koa Silviculture



Title:

Granting Agencies:

Project Period:



Silviculture of Regenerating Koa Forests

USDA, McIntire-Stennis and Tropical-Subtropical Agriculture Research Programs

Oct. 2003-Sep. 2008

   Koa restoration and reforestation has been successfully achieved across thousands of acres of upland ranches and degraded pasture lands on both public and private lands. However, little professional silvicultural management of these regenerating stands is taking place. Several management priorities have become apparent, such as controlling competition with shade- tolerant grasses, thinning overstocked stands, and potential P limitations to growth. Good silvicultural management may not only improve the growth and quality of the koa itself but also improve the habitat conditions for other native plants and animals. A study has been initiated in one set of stands to investigate the response of koa productivity to thinning, grass control, and P fertilization. Our research will investigate the effects of these experimental treatments on soil nutrient availability and supply, koa nutrition, and nutrient cycling processes.

   Currently, diameter increment growth of koa is being measured periodically. Results suggest that dbh growth of released trees in thinning plots are significantly improved when combined with grass control and P fertilization. Fertilization has a significant effect on soil P availability, increasing it by more than an order of magnitude. Now, more than 4 years after fertilization, available P remains much higher than background levels. A small portion of this can be traced to increased litterfall and litter P deposition rates. However, a significant portion of this fertilizer P remains in geochemical fractions with presumed "active" and "slow" cycling rates. The ability of koa to maintain access to this P or prevent it from fixation in the reactive volcanic minerals over the long-term is unknown. The soil mineralogy suggests rapid fixation should occur, but the high organic matter content of these soils may be masking the surface charge properties of the soil minerals.

 
DBH Growth of Selected Trees
Soil P Availability

Publications:

Meason DF, Idol TW, Friday JB, and Scowcroft PG. 2009. Effects of fertilisation on phosphorus pools in the volcanic soil of a managed tropical forest. Forest Ecology and Management. in press. doi:10.1016/j.foreco.2009.04.001

Meason D and Idol TW. 2008. Comparison of ion exchange resin membranes (PRS-probes) with resin bags in the field: effects of incubation time, soil depth, and P fertilization. Soil Science Society of America Journal 72:1806-1814. doi:10.2136/sssaj2008.0010

Scowcroft PG, Friday JB, Idol TW, Dudley N, Haraguchi J, and Meason D. 2007. Growth response of Acacia koa trees to thinning, grass control, and phosphorus fertilization in a secondary stand in Hawaii. Forest Ecology and Management 239:69-80. doi:10.1016/j.foreco.2006.11.009

Future Directions:

We are now expanding this work to younger koa stands in older, deep ash soils along the Hamakua coast. These stands are expected to respond more rapidly to thinning and P fertilization. The youngest stands are also expected to benefit from grass control, which is highly competitive with native plant seedlings. This work is being combined with new grass control techniques developed by Dr. James Leary to improve koa restoration in abandoned pastures.

 

 

2005 Koa Inventory

 

Peristent Grass Understory

 

Tree fern regeneration

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Forest Health Assessment




Title:

Granting Agencies:

Project Period:




Monitoring of Forest Health in Hawaii

US Forest Service, Forest Health Monitoring Program

Oct. 2003-Dec. 2009

   The health of Hawaii's forests is threatened by a history of land conversion, grazing, fires, and subsequent invasion of non-native species, including fire-prone exotic grasses such as fountain grass (Pennisetum setaceum). Restoration involves fencing, removal of ungulates, and control of exotic grasses and other plants. Further threats to native forest come from introduced pests and diseases.

   Accurate mapping of land cover type and forest health is a major goal of the US Forest Service, Forest Health Monitoring and Forest Inventory & Analysis (FIA) programs. They have developed guidelines for evaluating the health and vigor of closed-canopy forests. Unfortunately, the high spatial variability of Hawaii's landscapes and ecosystem types precludes the straight-forward implementation of the sampling protocols developed by FIA for the continental US. Instead, we have chosen to take advantage of the availabilty of high-resolution satellite images to classify and map land cover type and assess forest productivity and health status. Using archival images from the IKONOS satellite available from the Hawaii IKONOS Consortium, we were able to obtain full-color images at 1-m resolution and near infra-red (NIR) at 4-m resolution. Using object-oriented image analysis techniques, we accurately distinguished tree canopies from surrounding grasses and bare lava. We were also able to estimate tree canopy cover at the landscape scale.

Land Cover Types from Satellite Image Analysis
satellite

Publications:

Morales RM, Miura T, and Idol TW. An assessment of Hawaiian dry forest condition and restoration potential with fine resolution remote sensing. Forest Ecology and Management 255:2524-2532. doi.org/10.1016/j.foreco.2008.01.049

Future Directions:

We have combined the koa productivity work detailed above with the remote sensing tools developed in this project to map forest cover and health status, specifically of native and restored Acacia koa forests at the landscape scale. Standard forest structure and productivity indicators suggest tree canopy reflectance can be used to classify koa forests into productivity micro-regions that relate to differences in stand structure and productivity. Although IKONOS images are adequate for these landscape-level assessments, we are planning to use images from the newer GeoEYE-1 satellite, which provides higher resolution and potentially the ability to map the productivity and health status of individual tree crowns.

Classified Image: Forest Productivity Micro-Regions
HAVO

Comparisons Among Micro-Regions
productivity

 

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Agroforestry Projects



Restoration Agroforestry

  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).

   Results show that 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.

Publications:

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.

Future Directions:

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.

Native Plants for Agroforestry Restoration

Palapalai Regeneration-Lower Cleared Plot

Palapalai crown diameter

Lei-Making with Harvested Palapalai Fronds

 

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Shade Coffee Analysis

Title:

Granting Agency:

Project Period:

Development of Shade Coffee Agroecosystems In Hawaii

USDA, Tropical and Subtropical Agricultural Research

Oct 2003-Oct 2006

 

   The quality of Hawaii's coffee is generally regarded as among the world's best. Part of this reputation comes from the fact that most coffee has traditionally been grown in the uplands of the Kona region on the Big Island, where cooler temperatures, afternoon cloud cover, and volcanic soils create ideal growing conditions for coffee. In this region, tree shade has not been seen as necessary to ensure quality coffee production. As coffee has expanded across the islands into less-than-ideal growing areas, irrigation and fertilizers have maintained productivity levels in the face of potential increased stress to the plants. The effects of shade on the quality of the coffee produced: bean size, number of defects, and brewed flavor (organoleptic properties), is unknown, but research elsewhere suggests higher temperatures and greater sun exposure reduce certain aspects of quality. Because these larger farms are highly mechanized, trees would interfere with efficient operations. An alternative to tree shade is the use of a spray-on shade, a slurry of purified kaolinite powder sprayed on the leaves to reduce leaf irradiance, temperature, and light and water stress. We are comparing tree shade, black and aluminized shade cloth (40% light reduction), and the spray-on shade for their effects on coffee growth and yield, ecophysiology, and the quality of the beans themselves.

Early results demonstrate the light and temperature reducing properties of the shade treatments, including the kaolinite spray. The number of passes made with the sprayer over the leaves is linearly related to the reduction in UV light and light within the photosynthetically active range (PAR). It appears that 2-3 passes with the kaolinite spray equals the amount of light reduction due to the shade cloth. In the field, leaves sprayed with kaolinite have the same reduction in temperature as leaves under artificial shade cloth (4-5oC). However, their specific leaf area (SLA, cm2/g) and chlorophyll concentration are similar to sun leaves.
Light Reduction by Kaolinite Spray
Leaf Characteristics Under Shade Treatments

 

Coffee yields for the first season show a reduction for the shade cloth treatments but not for the kaolinite spray (see graph to left). In the second year, kaolinite yields were double that of full sun plants! In Kona, the aluminet shade plant yields were similar to full sun in the second year. Coffee quality parameters were somewhat improved with shade, but there is probably no marketable increase in quality. However, biochemical analysis of volatile chemicals emitted by the brewed coffees allows for highly accurate discrimination of growing location and shade treatments. This has promise for authenticating coffee origins and agricultural practices.

 

 

 

Publications:

Idol TW, Steiman S, Bittenbender HC, Gautz L, and Jackson, M. 2007. Not all shade is created equal: reflections on shade management based on preliminary studies from Hawaii. Second International Symposium on Multi-Strata Agroforestry Systems with Perennial Crops. Sept. 17-22, 2007. CATIE, Turrialba, Costa Rica.

Steiman SR, Idol TW, and Bittenbender HC. 2007. Analysis of kaolin particle film usage and its application on coffee. HortScience 42:1605-1608.

To view a short video describing this particular research project, go to the T-STAR Highlights webpage and click on the "Coffee Under Cover" video link. The Windows Media Player file is very large (55 Mb). The RealMedia file will play while it loads, but it is not downloadable.

Future Directions:

I am now collaborating with Craig Elevitch, the director of Agroforestry Net, Inc. on an evaluation of shade coffee systems in Hawaii. We are comparing farms with different levels of shade, different tree species, and different farming practicies (organic or conventional, irrigated vs rain-fed) that are spread throughout the South Kona coffee-growing region. Dr. HC "Skip" Bittenbender is working with a large commercial coffee grower on applying kaolinite spray at an operational level. We hope to recruit a scientist to study the ecophysiological effects of kaolinite applications. Shawn Steiman is applying his biochemical analyses to a broader range of coffee samples in order to better develop correlations with quality parameters and authentication of coffee origins, varieties, and growing practices.

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Agroforestry C Sequestration

   Agroforestry systems have a much greater inherent C sequestration potential than agronomic systems without trees. Increased plant, litter, and soil C can be sequestered in components with short to long turnover times. This may be enhanced through the incorporation of N-fixing trees, since soil organic matter has a highly conserved C:N ratio. Optimizing crop productivity with C sequestration requires the appropriate selection of crop and tree species and management practices.

   We have chosen to investigate the C sequestration and productivity potential of a shade-coffee agroforestry system. The tree shade is provided by a hybrid of Leucaena leucocephala developed at the University of Hawaii. The hybrid grows fast and responds well to pollarding, resprouting vigorously after cutting. We have underplanted coffee seedlings within an existing leucaena stand and out in the open in an adjacent field. Pruning frequency is also being manipulated to determine the optimal trade-off between coffee growth and net ecosystem C sequestration. Leucaena prunings are being chipped and mulched back into the shade plots and in half of the open-grown coffee plots to investigate a "cut-and-carry" system for weed control, soil improvement, and C sequestration. Measurements are being taken of C pools and flux rates from plants and soils.

   Early results indicate much higher soil C and nutrients underneath the leucaena stands, but mulch additions to open-grown plots can also improve soil C and N. This translates into improved growth and nutrition of the coffee plants. Under shade, soil temperature is lower, mulch decay is faster, and soil respiration rates are higher. Pollarding of the trees leads to a temporary "shock" to the coffee seedling leaves that developed under shade.

Publications:

Youkhana A and Idol TW. Tree pruning residues increase soil C and N in shade and full sun coffee agroecosystems in Hawaii. in preparation.

 
Leucaena KX2 stand

Leucaena root system

Effects of leucaena mulch

 

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Last modified: May 18, 2009