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.
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.
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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 2 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 actively cycled fractions of
soil P. The ability of koa to maintain access to this P or prevent it
from sequestration in the reactive volcanic minerals is unknown.
DBH Growth of Selected Trees
 |
Soil P Availability
 |
Publications:
Meason D and Idol TW. 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. accepted.
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. 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
to improve koa restoration in abandoned pasture.
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2005 Koa Inventory
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Peristent Grass Understory
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Tree fern regeneration
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Dry Forest Health and Restoration Potential
Title:
Granting Agency:
Project Period:
|
Monitoring of Dry Forest Health in Hawaii
US Forest Service, Cooperative Agreement
Oct. 2003-Sep. 2008 | |
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Dry forests are among the most threatened ecosystems in the tropics. In
Hawaii, most of the original dry forest has been converted to urban and residential areas,
agriculture, and grazing. Remnants of intact dry forest are often degraded due to past grazing and
the continued presence of feral ungulates. Exotic grasses and have invaded many of these areas, e.g.
fountain grass (Pennisetum setaceum). Restoration involves fencing, removal of ungulates,
and control of exotic grasses and other plants. Under intensive restoration, natural regeneration of native plants
may occur, especially in wet years. However, the overall health of the remaining native trees and
shrubs may not recover for many years. What is needed to supplement the ecological restoration of
these systems is a forest health evaluation system that can be used to prioritize restoration and
monitor the response of restored ecosystems. Developing such a system is the objective of this
project.
The Forest Service Forest Health Monitoring and Forest
Inventory & Analysis
programs have developed guidelines for evaluating the health and vigor
of closed-canopy forests. These are mostly visual indicators of canopy
health, e.g. canopy transparency, live crown:tree
height ratio, tip and branch dieback, and symptoms of pathogens or parasites.
We are adapting these visual cues for use in Hawaii's dry forest ecosystems
and adding other indicators: abundance
and diversity of canopy insects; mycorrhizal colonization of fine roots;
leaf mass/area, leaf nutrient concentration, and evidence of herbivory;
and various measures of plant cover and diversity. Preliminary
data suggests that the health of some trees that are vulnerable to degradation,
such as kauila (Colubrina oppositifolia), responds positively to long-term
restoration. More conservative and slow-growing trees that are resistant to degradation, e.g. lama
(Diospyros sandwicensis), do not show a health response to restoration. Colleagues with the
Forest Service suggest lama may increase its photosynthesis and water use under restored
conditions, but these ecophysiological improvements have not yet translated into greater canopy
density, reduced dieback, or lower incidence of parasitism or disease. Removal of ungulates and
control of invasive grasses allow for natural regeneration of native plants, especially during wet
years. However, they must be able to survive dry years for restoration to be called a success.
| Degraded Dry Forest
|
Uhiuhi Regeneration
in a Restored Site
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Dr. Miura and I have collaborated on a new project
to map remaining dry forest cover using multi-spectral satellite images
(Ikonos). Rodolfo Martinez-Morales has used new object-oriented image
analysis to distinguish different forest cover types and identify tree
canopy from surrounding cover types. This allows us to identify areas
with higher cover and thus higher potential for restoration at the landscape
scale. It can also be used to track changes in land cover types over
time.
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. in press.
Future Directions:
We will combine 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 health assessments will be used to ground-truth remote sensing
estimates.
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Land Cover Types from Satellite Image Analysis
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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 a sustainable agroforestry
system of 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 oliviformis),
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).
The plot design is illustrated below. 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.
Survival of inkberry seedlings is lower under
the most exposed conditions, but growth of the surviving seedlings
is
greater. Total weed regeneration has declined significantly over
the 2 years of clearing, and replanting with native species improves
weed suppression. This suggests that this 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
 |
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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 stand prior to pollarding
|
| Coffee planted under
leucaena
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New agroforestry planting
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Last modified: April 14, 2008
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Environmental
Controls Over Acacia koa Productivity
