Oak Decline and the Future of Missouri’s Forests

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Published on: Jul. 2, 2002

Last revision: Nov. 12, 2010

Faint gnawing sounds come from within the trunk of a large black oak in an Ozark forest. A red oak borer, a large wood-boring beetle with very long antennae, is chewing through the bark, preparing to emerge from the tunnel where it has been living for the past two years.

Millions of oak borers emerged during the summer of 2001 in Missouri and Arkansas, and we'll likely have even higher numbers chewing through our oaks in the near future.

Populations of the red oak borer and other wood-boring insects are dramatically increasing throughout the Ozarks. Oak-attacking fungi have also become more active. Their increased attacks on oaks are part of a phenomenon collectively called oak decline. This condition has worsened in the Ozarks recently due to a few years of drought and the advancing age of many oaks, resulting in an ever-growing number of dead and dying oaks.

Although declines have occurred at times in the past, the current episode is unique. Missouri's early history of poor or no management, over-harvesting, burning, grazing and other practices set the stage for oak decline.

Trees take a long time to mature. In the late 1800s and early 1900s, Missouri's forests, many of which contained a healthy mixture of shortleaf pine, and black, white, scarlet and post oaks, were logged on a grand scale.

By the 1920s, most of our large trees had been cut. Subsistence farmers and ranchers burned the cut-over lands to encourage grass growth. Frequent burning killed pine seedlings but encouraged hardwoods to re-sprout, resulting in the hardwood forests we have today.

Most of the trees affected by oak decline are in the red oak group. the species most severely affected are black oak (Quercus velutina) and scarlet oak (Quercus coccinea). Many of these trees have managed to survive on shallow, rocky soil on broad ridges or south- and west-facing slopes, less than ideal conditions for red oaks. Often the stands are crowded with large numbers of trees that are at least 70 to 80 years old.

Oak trees growing under these conditions become physiologically stressed as they have to compete heavily for limited water and nutrients. Older trees are less vigorous than younger ones and can't withstand repeated attacks by diseases and insects. A multitude of stresses inevitably weakens a tree to the point that it only produces dwarfed, sparse foliage, and its crown becomes thin. Branches in the upper crown die back from the tips as

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