Dr. J. B. Friday
CTAHR | University of Hawaiʻi
Cooperative Extension Service
875 Komohana Street
Hilo, HI 96720
Telephone: (808) 969-8254
Fax: (808) 981-5211
Email: jbfriday@hawaii.edu

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Field Day at Kukuaiu Ranch

Koa pasture scarification, silvopasture, and plantation

August 17, 2009 ~ Kukaiau Ranch

Koa forests can be restored to upland pastures in Hawaii either by soil scarification to stimulate germination of buried seeds or by planting. Cattle may be able to graze in open koa stands in silvopasture systems, but cattle eat the tops of young koa and may damage roots and introduce diseases even in older trees. Most koa plantations have been damaged by livestock and have very low potential timber yield. Here we demonstrate different methods of soil scarification and herbicide use to regenerate koa. We also investigate timber yield and quality from a nearby 33-year-old koa plantation.


University of Hawai‘i at Manoa
College of Tropical Agriculture and Human Resources

USDA Forest Service Institute of Pacific Islands Forestry

Kukaiau Ranch


USDA Natural Resource Conservation Service Conservation Innovation Grant, http://www.nrcs.usda.gov/programs/cig/, Hawaii contact: Mike Whitt, Resource Conservationist, USDA NRCS (Honolulu), 808-541-2600 ext. 153, michael.whitt@hi.usda.gov.

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Herbicide application for grass suppression for koa establishment

Cattle were removed from this pasture in August 2008 and lines sprayed with imazapyr (applied at 1 qt/acre) in September 2008. Photos were taken February 2009.The herbicide was effective in the healthy kikuyu grass growing under the residual koa canopy in some spots. .The herbicide was much less effective in open areas of dense kikuyu grass.While there was some injury to the treated kikuyu grass, the single application of imazapyr was not enough to cause mortality. A second application of imazapyr plus glyphosate applied at 1 qt/acre was made in March 2009.A few koa seedlings were observed germinating in the treated kikuyu grass.Koa seedlings were observed in areas where a bulldozer had passed, indicating that there is still a viable seed bank in the area.

Soil scarification for koa establishment [photos by J. B. Friday]

Using a pasture aerator the scarify for koa regeneration. The weight on the rolling drums causes the spikes to sink into the soil.The effect of the spiked pasture aerator in a mowed strip and a strip where herbicide had been applied.The disk used for scarification.scarification.   	  The disk in action, turning over the sod.A strip where herbicide had been applied 3 months previously vs tall grass in an untreated area that had not been grazed for a year.Mowing to knock down the tall grass in advance of scarification. The field had not been grazed for a year. Under operation conditions, a field could be grazed immediately before cattle are excluded and the area is scarified.The disk turns over the sod and disturbs the site more than the aerator.

Experimental harvest of five koa trees in the 33-year-old “cornfield” plantation at Kukaiau Ranch [all photos are by J. B. Friday except for photo 9 by Jian Wang.]

The “cornfield” koa was planted in 1976 by the USDA Forest Service as a demonstration that koa reforestation could work in upland pastures on Mauna Kea. The trees originally were planted at 4 x 4 foot spacing and were never thinned. Today, probably half of the trees have died fro rel="lightbox[harvest]" title="my caption"m overcrowding.About twelve trees in the plantation had potential as future crop trees. These were marked with a single blue ribbon. “Cull” trees are trees that would be removed in a thinning operation to allow the crop trees to grow. Four of these were marked with double blue ribbons and measured.Four “cull” trees and one “crop” tree were felled for determination of wood yield and quality. This cull tree was 15.1 inches dbh.Logs were measured and scaled; this log scaled out as 70 bf Scribner, not allowing for defect.Butt log of cull tree showing sapwood and heartwood. Only the heartwood is merchantable.Logs were milled on site and tally was kept of yield of individual logs. This cull tree yielded 42 bf net. The wood was light in color with little figure.Some curl developed in the branch forks.Twelve trees in the plantation had potential as crop trees. Tree 1 had a dbh of 20.2 inches and was harvested for determination of yield and wood quality. Photo by Jian Wang.Logs were milled on site on a Wood-mizer band saw.Decay resulting from injuries years previously ran through the logs causing a significant loss in yield.Crop tree 1 yielded 200 board feet. Lumber was light in color with little figure.

Handouts from the field day (all files in pdf format acrobat reader icon)

References for further reading on koa