Outbreak of native oak borers threatens Ozark forests

November 21, 2002

Preliminary results from biomonitoring studies by USDA Forest Service researchers confirm an unprecedented outbreak of red oak borers in the upland hardwood forests of the Ozark and Ouachita Mountains in Arkansas, Oklahoma, and Missouri.

Jim Guldin, research ecologist with the FS Southern Research Station (SRS) and project leader of the SRS Upland Forest Ecosystems unit in Monticello, AR, recently announced the results of a pilot study started this summer to quantify the extent of the outbreak. Designed to provide more information about the distribution of the insect, the plot-based study is funded by the Forest Service, with the research conducted by scientists from SRS, the University of Arkansas at Fayetteville, and other agencies.

The red oak borer, an inch-long beetle native to forests in the eastern United States, causes most of its damage while in the larval stage of a two-year life cycle. The larva burrows through the bark of the oak, carving out galleries in the cambium and the heartwood of the tree. The adults emerge from the oval holes they chew in the bark in odd-numbered years. The red oak borer is usually an insignificant pest that oaks can easily fend off, but since 1999, when unusual levels of infestation were found by the Forest Service near Clarksville, AR, the density of red oak borer populations has steadily increased.

"What we found in our preliminary results confirms an explosion of oak borer infestations," said Guldin. "Outbreaks once consisted of five to 10 borers a tree: now we are seeing 1500 a tree. At this level of attack, the insects literally girdle the tree: tens of thousands of trees have died so far."

During the summer of 2002, researchers installed a pilot study on 44 plots, primarily on National Forest land in Arkansas and Oklahoma."Traditional plots established by the Forest Service for forest health monitoring cannot capture the extent of the problem because the plots are too dispersed and not visited frequently enough," said Guldin. "We need an intensive and wide-scale sampling effort to predict how long this epidemic will last."

Half of the red oaks on the 44 plots were dead, with no new sprouts evident. Ten percent of the white oaks were dead and dying. Based on the preliminary counts from the biomonitoring studies, Guldin estimates that 25 percent--possibly up to 33 percent--of the red oaks of the interior highlands of Arkansas and Missouri will be lost. Guldin believes that the effect on the forests of Oklahoma may be even worse. Guldin emphasizes that results are preliminary and may change with further sampling in the coming year.

Researchers are not sure why this current cycle of infestation has proven so devastating to the red oaks of Arkansas and Oklahoma. Drought and attacks by other insects such as walkingsticks and grasshoppers, combined with the advanced age and high density of the oak stands, may have contributed to a general state of decline that has left the oaks particularly vulnerable to red oak borers.

"Right now we are in the middle of a cycle," said Guldin. "We will learn more when the adults emerge this coming summer. It is very troubling that the oaks killed by borers do not produce sprouts that grow into new trees. If the red borer continues at this level, we may see a significant reduction in the red oak component in the forests of the Interior Highlands that will last for decades."
-end-


USDA Forest Service ‑ Southern Research Station

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