Psyllid May Be Cause of Forks Seen in Plantation Koa Stands

posted in: March 2012 | 0

When it comes to the prospects of growing high-value koa in plantations, Hawaiian Legacy Hardwoods CEO Jeffrey Dunster and University of Hawai`i forester J.B. Friday do not see eye to eye.

They disagree over the yields of marketable koa that can be expected from a given area, with Dunster predicting productivity rates more than twice those reported by Friday.

They also disagree over the quality of the wood, especially when it comes to the production of the tall, straight trees highly valued in hardwood markets.

When it comes to the prospects of growing high-value koa in plantations, Hawaiian Legacy Hardwoods CEO Jeffrey Dunster and University of Hawai`i forester J.B. Friday do not see eye to eye.

They disagree over the yields of marketable koa that can be expected from a given area, with Dunster predicting productivity rates more than twice those reported by Friday.

They also disagree over the quality of the wood, especially when it comes to the production of the tall, straight trees highly valued in hardwood markets.

In the journal Small-scale Forestry, Friday, Travis Idol (also with the University of Hawai`i), Paul Scowcroft and Janis Haraguchi (both with the U.S. Forest Service in Hilo), and Nicklos Dudley (with the Hawai`i Agriculture Research Station) published a paper called “Poor Stem Form as a Potential Limitation to Private Investment in Koa Plantation Forestry in Hawai`i.” As the title suggests, they found that “most existing plantation koa trees fork so close to the ground that they will produce little to no merchantable wood.”

“The product in forestry ventures is often sawtimber, which requires trees with straight, single-stemmed, defect-free trunks,” the authors write. Often, plantations of high-value hardwood trees “tend to produce low-value, short butt logs and bolts due to crooked stems, low fork heights and delayed shedding of lower branches.”

The plantation koa studied by the authors follows that pattern: “few plantations contain large proportions of well-formed trees that might one day yield sawlogs. Instead, plantation trees generally appear to have multiple trunks originating within 3 m [meters] of ground level, a growth form unlikely to yield much merchantable wood.”

Dunster argues that his company has the benefit of knowing the source of its seeds and that, by tracking seedling growth from one year to the next, his workers can figure out which seed sources are most successful and eliminate the less successful ones from their future plantings.

Of the first 20,000 seedlings planted, Dunster said, “none of them forked. We did notice differences in growth, though, and we monitored that over the next year. We started to notice trends – certain trees were really vigorous, strong, and straight…. In year two, we selected trees for planting and refined our mix. Year two trees are faster [growing], more vigorous…”

Friday is not so sure that the HLH trees will escape the same fate as other plantation koa, however. While superior genetics helps, he told Environment Hawai`i, there’s also the koa psyllid, Psylla uncatoides, to deal with.

“Koa wants to be a big tree,” Friday said. “It’s in its architecture. But if bugs come in and kill the terminal leaders, they branch out. At Umikoa [a neighboring ranch where koa has been planted], every single tree is forked.

“What I guess happened is, all the plantations were hit by psyllids. They take off in summer and nail the terminal leaders… At Umikoa, all the trees forked at six feet. If it was three feet, you’d suspect cows were responsible. But at six feet, it’d have to be a pretty tall cow. I suspect they got hit by psyllids.”

“To get a straight tree,” he continued, “everything has to be right – good genetics, good environment. But if you kill the top, you’ll get branching.”

Patricia Tummons

Volume 22, Number 9 — March 2012

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