MICHEL MARTIN, HOST:
Why are bur oak trees, also known as Kings of the Great Plains, dying? Harvest Public Media's Jackie Ourada takes us to Nebraska.
JACKIE OURADA, BYLINE: At the base of the observation tower in eastern Nebraska's Mahoney State Park is a graveyard where giant bur oak trees once stood. Horticulturist Noah Sundberg removed 75 oaks here that died in the direction of the southerly winds.
NOAH SUNDBERG: They were dying from the tips down. And we noticed in this specific area, it was almost a wedge effect.
OURADA: The widespread oak mortality started to show in 2023 and was a mystery to park officials. Test results eventually confirmed hypoxylon canker, a disease-causing fungus, was running rampant with help from a five-year drought.
SUNDBERG: We're seeing change at an accelerated rate that they can't adapt as readily. So these 150-, 200-year-old oak trees just can't handle the conditions of today.
OURADA: The U.S. Forest Service, in a 2023 report on forest insects and diseases, said climate change is dialing up the effects that disturbances such as fires, flash floods and drought have on trees across the country. And in turn, pests and pathogens have more opportunity to attack. Usually, the fungus isn't an issue for Midwestern trees, but it's caused mortality in the South for years. Clarissa Balbalian, a diagnostician and lab manager with Mississippi State University, helped horticulturists in Nebraska identify the disease.
CLARISSA BALBALIAN: By the time you've seen it, the tree has been under stress for so long that it's probably irreversible at that point. It's just in a decline spiral.
OURADA: Hypoxylon canker also recently affected trees in other Midwestern states like Kansas and Iowa after extremely dry periods there. University of Illinois forestry specialist Chris Evans saw thousands of oaks die following the 2012 drought, one of the worst in recent history.
CHRIS EVANS: It was just constant calls about, why is my tree dying? What's wrong with my tree? A lot of trees died for us over a bigger area.
OURADA: Beside the widespread cases in southern Illinois, hypoxylon canker also severely affected trees in Missouri. At the time, Evans recommended property owners replant with trees that could survive a future with less water.
EVANS: Instead of a pin oak, maybe think about a black oak or a white oak, or move over to other species in general. Maybe black gums. Some of the hickories are more resistant, as well.
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OURADA: In Nebraska City, a town designated as a Tree City of the World and the founding home of Arbor Day, arborists are also figuring out how to hold on to their tree canopy during drought. For Rob Schreiner, chairman of Nebraska City's Tree Board, it's hit close to home.
ROB SCHREINER: I've lost two in my yard this year, and one of them is just - it was absolutely gorgeous last year. It showed no signs.
OURADA: Now he's introducing newer species to town that may have better luck through wild swings in weather.
SCHREINER: I'm doing a lot of experiments now with the Japanese maples, having really good luck with those. They've come out with some new hybrid elms, which so far have been out for quite a while, and they're really doing well.
OURADA: While more oaks will be cut down throughout Nebraska's state parks this winter, their stories may not be completely over. Months after forestry crews cut and burned the dead oaks at Mahoney State Park, they noticed resprouts starting from several stumps, sowing hope that the mighty native Nebraska oaks - the King of the Great Plains - might one day return.
For NPR News, I'm Jackie Ourada in Ashland, Nebraska.
(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.
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