Thinning, Fertilization and Herbicide Trials to improve Koa production

Thinning, Fertilization and Herbicide Trials to improve Koa production


Thinning, Fertilization and Herbicide Trials to improve Koa Production CTAHR virtual field day: Umikoa Ranch November 2008 Hi. I’m J.B. Friday with the UH Cooperative Extension Service and we’re here today to talk about research in
managing young koa stands. Over the past century a lot of hawaii’s upland forests
were turned into cattle pasture. Recently there’s been a lot of transition away
from cattle pasture back into native forest. The most common thing to do is to fence the area, get rid of the cattle, and then scarify the soil to allow the
forest, especially koa, to regenerate. Here we’re standing in a koa stand. This area was a cattle pasture 10 years ago. What the landowner did is he fenced it, moved out the cattle, and then scraped the surface of the soil with a bulldozer.
This is called scarification and what it does is it stirs up the koa seed that’s
buried in the soil and allows it to sprout. As you can see it worked very
well to regenerate the stand. 10 years later, we have 2700 trees an acre on these, and the trees have reached 35 to 40 feet tall. In this stand we went through and we selected the better trees in terms of the ones that were
straighter, didn’t have forks in them. But even these trees are growing at about a third of an inch a year Koa Thinning Trials Because of the high density to the stand,
there are so many trees an acre, the trees are competing with each other and the individual trees are growing slowly. When we look up into the canopy, we can
see the tree crowns are packed in very densely and shading each other. This
reduces the growth of the individual trees. Here we’re in a new site where we
conducted an experimental thinning, we selected crop trees, and then we released them from competition by cutting all the other koa trees within a 15 foot radius
of the boles. We went into this stand and we selected the better trees that had
the potential for being crop trees for timber. For example this one is a
straight bole and it doesn’t have any forks, as opposed to this one over here
that has a fork at about six feet above the ground. In the gaps that we created
by thinning, the crowns of the crop trees receive a lot more light. In the past year and a half since we released this crop tree, it has grown over an inch
in diameter. We found that in some forests, koa responds to phosphorus
fertilizer, so as part of the experiment here, we applied about nine pounds of
triple superphosphate to each tree. Herbicide trials to suppress invasive grasses during koa seedling establishment When we created this gap in doing our
thinning, a lot of light got to the forest floor and what happened is the
grass and the other weeds grew back really quickly. Now grass competes with trees, so
here we’ve invited Dr. James Leary at the University of Hawaii to work on
controlling the grass and the weeds under the trees. So Jim, can you tell us
what you’re doing as far as controlling the weeds here? Sure J.B. Today I’m going to make a herbicide application and i’m using my 12-volt backpack sprayer, and
I’ve modified the tip with a off-center tip that actually throws a distance of
four meters. And so what we’ll do is I’ll circumvent the tree so that we get a
nice four meter radius swath around the entire tree, so hopefully, hey you know
within sixty to seventy days, we should have a real good suppression of this
grass. So the herbicide i’m going to use today is imazapyr in the form of
Arsenal PowerLine, and some of the research i’ve been working on I’ve
noticed that the PowerLine is very effective on controlling kikuyu grass
and other weeds, but koa seems to have really good tolerance on it. So it has
real good selectivity in this case. And so this is what iʻm using, iʻm going to be applying at about 1 quart per acre rate. And that’s it. One year later – November 2009 Here we are one year later, on one of
these plots where we applied herbicide. Now you can see that the herbicide was
quite effective on the kikuyu. When we visited this plot three months after applying herbicide, we just saw it beginning to take effect. After 6 months we had seen a pretty good kill, and now after one year the kikuyu grass
is still dead. So this shows us that the imazapyr has a long-term effect, and
that one application of it was enough to take out the kikuyu grass. In some of our
other plots, we also have other weeds such as thistle, and the imazapyr was
effective on those. The crowns of the trees that we liberated in our thinning process have been expanding over the past year and are expanding to fill the
spaces and the gaps that we created. Here we’re measuring the width of the canopy using a height pole here to line up with the edge of the canopy and a measuring
tape. We calculate the area of the canopy and then we see how that canopy expands over the years to fill up the gap we’ve created. In plots such as this one where we applied an herbicide to kill the weeds, we see a trend towards the canopies
expanding quicker than we do in the control plots. We expect the diameter of the trees to follow up on this as the tree expands its canopy first, then grows a
greater bole diameter. This may take a long time, so we’ll be following up on this research for a number of years. We’re also sampling soils here to look
at phosphorus and look at pH. In the areas we applied phosphorus, our soil sampling shows that there’s increased levels of phosphorus in the soil, and
we’ve seen some increases in phosphorus and the tree leaves. What we haven’t seen
yet is any difference in the growth of the trees where they were fertilized. A
phosphorus fertilizer can take a long time to have effect, and once it has
effect, the effects can last for many years, and we’ve seen this in some other
forests in the island. So we’ll have to follow this for a number of years to see
what the results are. Dr. J.B. Friday
Dr. James Leary
Dr. Travis Idol Mahalo nui loa to Umikoa Ranch for hosting this research project. Mahalo to Dr. H.C. Bittenbender for his slack-key version of Manuela Boy. Tropical Sub Tropical Agricultural Research TSTAR
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