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White Oak Mortality in the Missouri Ozarks

Gary Grigsby
/
KBIA

In the past few years white oak mortality has killed an untold number of trees in the Missouri Ozarks.

A company called Pioneer Forest is located in the Missouri Ozarks and sustainably harvests timber on its vast holdings.  Holdings that are in the heart of the area hardest hit by white oak mortality.  It has lost a lot of white oaks in recent years and its managers have had to deal with it.  "This is a larger, healthy tree that you would expect to survive and it did.  We are happy with that," said Brandon Kuhn who is Pioneer's Forest Manager.  "Here's one here that looks like it died, or is dying.  We haven't seen much of that."  Kuhn is talking about white oaks in a stand we are walking through on some of its land in Shannon County.  "You can see the silver streaking on this tree, that's the hypoxylon canker.  That's what we feel like killed this tree."

Kuhn and I took this walk in December of 2014 when he wasn't seeing much of the hypoxylon canker anymore.  He felt the worst was over for the white oaks that make up 30% of the trees growing in the woods here.  But in 2012, Kuhn said the worst was just beginning.  "We had a late frost, killed the leaves on the white oaks in these low-lying areas.  Right after late frost we had a really bad drought," he said.  "That stressed those trees really bad.  We feel that canker was able to move into this area and kill these white oaks."

Once they saw what was happening, Kuhn says they began to take action and salvage many of the trees.  Kuhn's boss, Pioneer Forest Chief Forester Jason Green, was also in the woods with us in the woods a few months ago in an area especially hard hit by white oak mortality in 2012 and 2013.  I asked Green what the losses were, roughly, for every 100 white oaks on their land in low-lying areas.  "If we had 100 live white oak trees we would have cut probably 75 of them.  Probably 25% of them are left," Green said.  "Pretty severe.  We certainly wouldn't cut our timber normally this way."

Green said the white oak is a tough tree that lives a long time and is usually not prone to things like disease and drought.  "The interesting thing about this white oak mortality is it didn't discriminate based on size.  It didn't discriminate based on vigor.  It hit all class sizes.  All vigor sizes."

As for the white oaks growing higher up the hillsides, well, Pioneer's Brandon Kuhn said there were no problems at all basically for them.  "You could see a distinct line on the hillside, almost a frost line.  It only went up so high on the hillside and essentially the white oaks on the bottom had died from the hypoxylon and the stress of the frost and the drought and the white oaks up on the hillside survived." 

Credit Gary Grigsby / KBIA
/
KBIA
At a lab on the MU campus, research scientist Dr. Sharon Reed slices off bark from a white oak tree that died in the Mark Twain National Forest in southern Missouri. She's conducting tests to try and determine how insects or fungal pathogens in the bark might be contributing to white oak mortality.

Pioneer Foresters believe the hypoxylon canker they feel caused rapid white oak mortality on its land has run its course.  Others say white oak mortality is more complex than that.  "So I would be hesitant to suggest that any forest health issue is ever really done," said University of Missouri Forestry Professor Dr. Rose-Marie Muzika.  Muzika leads a team of scientists doing research on white oak mortality in Missouri.  Team member and MU research scientist Dr. Sharon Reed said a lot of things could be at play in addition to the hypoxylon canker that hit those Pioneer Forest white oaks so badly.  "Right now we are just trying to understand if there are any insects or any type of pathogens, fungal pathogens specifically, that are involved in the decline of the white oak trees."  The research is being funded by the Missouri Department of Conservation and the U.S. Forest Service.