Eastern Nebraska’s Bur Oak Trees, Known as the ‘King of the Great Plains,’ Dying Due to Widespread Drought

By: Jackie Ourada, All Things Considered Host - Nebraska Public Media

Published June 24, 2025 | Article republished with permission

Dead trees line the Salt Creek and Platte River near Mahoney State Park in June 2025. Horticulturists with the Nebraska Game and Parks Commission were stumped when they started seeing significant dieback in many of their old bur oak trees in 2024. (Photo by Jackie Ourada/Nebraska Public Media)

It’s difficult to spot the difference at the entrance of Eugene T. Mahoney State Park in eastern Nebraska. Drive a little deeper near the horse barns, and the death is more stark. Dotting the tree lines are towering ashy brown trees grasping onto their last shriveled-up leaves.

Farther into Mahoney Park, where its perimeter meets the Platte River and the giant observation tower stands tall, a graveyard of dark brown pits, the remnants of dead trees, greets park guests. Many of the remaining nearby oaks are bare with silver crusty patches wrapping like a grip around their trunks and branches.

What used to be a field full of shady, large bur oak trees is now home to tall grasses and weeds in June 2025. Nebraska Game and Parks crews cleared about 75 dead trees from around Mahoney State Park’s observation tower. (Photo by Jackie Ourada/Nebraska Public Media)

Noah Sundberg, a Nebraska Game and Parks horticulturist who’s cared for Mahoney Park’s trees for several years, first noticed the dieback among these bur oak trees in 2023.

“It brought some concern, but we weren't sure what was going on,” Sundberg said. “We thought the oaks could pull out of it.”

It became apparent when the summer of 2024 rolled around that some weren’t going to hold on anymore, and it wasn’t just a few of the park’s older bur oak trees. Dozens started dying.

What was once an area at Mahoney State Park crowded with leafy trees is now an open field with several remaining dead ones, leaving visitors and bright white concrete sidewalks to bake in the hot June sun. (Left photo taken by Dedham Go-Getter’s 4H Group of Iowa in July 2022. Right photo taken by Nebraska Public Media in June 2025.)

“It’s a night and day difference,” Sundberg said, peering out at a grassy field, where large, leafy trees had spent years giving park visitors reprieve from their treks up the tower. “An area that was once almost completely shaded by these oak trees is now full sun. On hot days, it's even hotter.”

The trees’ quickly declining appearances were out of the norm for Nebraska’s towering bur oaks. They’re some of the most common native oaks in Nebraska. But the once soaring and wide-canopied trees – known by some as the “King of the Great Plains native hardwoods,” since they’ve withstood hundreds of years of extreme Nebraska weather and varying pests – are dying en masse throughout eastern Nebraska’s deciduous forest.

An oak tree, estimated to be more than a century old, shows signs of stress. (Photo taken by Jackie Ourada/Nebraska Public Media)

As more trees started suffering, Nebraska Game and Parks horticulturists who’ve spent their careers monitoring the trees were puzzled. What started as brewing concerns at a few state parks last year has now quickly transformed into massive areas of tree mortality in at least seven Nebraska state parks – all along the state’s eastern half.

“We’re not talking square feet here. We’re talking acres,” Nebraska Game and Parks horticulturist Richard Whemeyer said. “I believe Ponca State Park has it the worst. We're seeing 70% loss of bur oak canopy – just large dead swaths of oaks on our ridge lines. We lost elms, we lost hackberries, we lost ash, red oaks. We've lost a lot of species, but the species that happen to be very prominent in these areas were the bur oaks.”

Nebraska’s historic Old Wolf Oak at Ponca State Park in June 2025. (Photo by Jackie Ourada/Nebraska Public Media)

Included in the large number of deaths was one of Nebraska’s oldest trees. Believed to have been planted in 1644, according to two cores drilled into the tree’s center, the Old Wolf Oak spiraled over Ponca State Park for more than three centuries. The Nebraska Game and Parks Commission announced earlier this year that whatever was plaguing some of Nebraska’s hardiest eastern trees had also taken out this behemoth, recording-holding bur oak tree.

“The trees that I have personally had to remove…they've been large, substantial trees,” Whemeyer said. “It's pretty disheartening, especially seeing trees that we, as arborists for the state park system… some of these trees we've worked on for years. And to see them go out so fast, like this... It's been sad.”

Game and Parks horticulturists spent months studying the symptoms, researching varying diseases and bugs. The crew finally sent samples off to its diagnostic lab, hoping to uncover a solution that could help save their historic trees.

The results identified a sneaky, tree-killing culprit that wasn’t one known to strike in Nebraska: hypoxylon canker. When the lab called Whemeyer back, they said he might find more answers down south.

A familiar foe in the South finds a home in Nebraska

Clarissa Balbalian, a diagnostician and lab manager with Mississippi State University Extension in Starkville, wasn’t surprised last summer to receive an uptick in calls from neighbors wondering why their oak trees weren’t looking too well. During the last half of 2023, Mississippi suffered from months of “exceptional drought” – the worst classification of drought on the National Drought Mitigation Center’s scale.

The dry conditions took a toll on a number of the southern state’s trees and ushered in a harmful caterpillar species and fungus to team up and feast on them. In years with regular moisture, neither would have left a significant mark on most healthy trees, but the severe drought dealt the trees “a compromised ability to defend themselves against any kind of trauma, including damage from insects and disease,” according to a news release issued last summer by the extension office.

Both tree irritants weren’t new to Mississippi. The caterpillar even arrives in two different generations to swarm the state’s trees during different points of the year. The fungus causes hypoxylon canker, which is a common oak tree killer in Mississippi. It’s known to take over rapidly if a tree’s defenses are knocked down.

“It's very cyclical, because it's closely linked with severe drought,” Balbalian said. “When those conditions ease, we get back into more favorable conditions for the trees, and we stop seeing the problem. Then people forget about it, because usually we're fine for maybe a decade or so, and then we have another really bad couple of years, and it pops up again.”

Hypoxylon canker pushed off large chunks of the Old Wolf Oak tree’s bark. After struggling from dry conditions and age, the record-holding tree died in 2025. Cores taken from the tree suggest it was first planted in 1644, making it the oldest known tree in the state. (Photo by Jackie Ourada/Nebraska Public Media)

The fungus is a normal part of a healthy tree’s bark. If it gets past the bark into the tree, high water pressure and natural chemical defense systems typically provide a strong shield that prevent it from overrunning the tree.

“But when we get into situations like you guys have been experiencing with the severe drought, especially in multi-year droughts, the moisture content in that wood is going to drop,” Balbalian explained. “And essentially your defense compounds are dropping with that, and it gives the upper hand to the fungus.”

Hypoxylon canker can attack a variety of tree species, but finds an especially fitting and familiar home in oak trees. There’s no cure or treatment that can save a tree once the fungus spreads and closes in on it. Eventually, hypoxylon canker will cause the tree’s sapwood vessels to collapse, which cuts off water and nutrient movement.

“It'd be like having a kink in a water hose or a tourniquet on your arm,” Balbalian said. “And when enough of that sapwood is compromised, the tree is going to die just from lack of water, essentially.”

When a tree is overrun with the fungus, it can start to develop smaller leaves toward the top of the tree’s crown; whole branches appear dead; leaves begin yellowing or wilting; and sapwood turns brown.

One of the most obvious indications that the fungus has established itself is when strips of bark start to pop off. That’s a sign the infection has put enough pressure under the tree’s bark to push the outer layer off. Underneath the removed bark will typically lie a beige, fuzzy strip, which will turn black as it ages, according to Balbalian. By the time hypoxylon canker is running rampant and physical symptoms appear, it’s typically too late to reverse course.

And what’s worse – when the fungal material is there, it’s producing spores that can spread to neighboring trees. It’s recommended to burn the trees and bury them to eliminate the possibility of the spores spreading.

Hypoxylon canker’s fast-moving proliferation quickly became evident in the heart of Mahoney State Park.

“It was almost a wedge effect,” Sundberg said. “It looked like it was one tree, and then it spread in the direction of the predominant wind. We get a lot of south wind here, so it looked like that fungus had spread and was killing the trees down the hill.”

To limit the spread of hypoxylon canker in a large forested area like Mahoney State Park, the Game and Parks crews decided to burn their dead trees. After watching them wither away during the remainder of last year, the crew of about 10 workers set up an operation in January near the tall observation tower to cut down the trees and burn them on the spot.

When the ash settled and the debris was cleared, the destruction caused by the hypoxylon canker really set in for the Game and Parks crew. The park was changing before their eyes – rapidly.

Damaging drought puts both rural and urban Nebraska tree lines in trouble

Those keeping an eye on Nebraska’s changing tree landscape include Laurie Stepanek, who’s specialized in forest management for the Nebraska Forest Service for more than 30 years. She knew hypoxylon was an issue for southern states, but it had never caused widespread issues for Nebraska’s trees before.

“Bur oak is generally a pretty tough tree,” Stepanek said. “It's more adapted to our Nebraska conditions. It seems to be pretty tolerant to a lot of urban-type stressors, such as air pollution. It’s a pretty tough tree for our climate.”

Stepanek has seen a number of pests, diseases and even human-caused stresses, such as pesticide use and construction, harm trees, but she hasn’t seen Nebraska’s notoriously dry weather take a toll like this on Nebraska’s oak woodlands.

“I can’t say I’ve seen the massive die-off of oaks like we're seeing currently,” Stepanek said. “Bur oaks have been known as a drought-tolerant tree, but I think that the drought conditions we've had in the past four or five years have been so severe and prolonged that it's affecting some of these older bur oaks.”

Drought conditions have been lingering in eastern Nebraska since the 2019 bomb cyclone that washed out a dam, crumbled several major bridges and flooded a handful of Nebraska towns. Since that deadly flooding event, parts of eastern Nebraska have seen a large deficit in precipitation, according to the National Weather Service. Not only is the state seeing a drop in timely summer showers, it’s not receiving adequate snow cover in the winter, either.

According to the National Weather Service’s official climate-tracking station in Lincoln, the Capital City has seen a deficit in precipitation – in both rainfall and snowfall – of about 2 feet since 2020. Three out of the last five years fell more than five inches short of normal precipitation, which is compared to accumulation data between 1991 and 2020.

The largest shortfall between that time period was in 2022, when the Lincoln climate site only recorded around 20 inches of rainfall or snowmelt, which is about nine inches short of the normal annual accumulation.

And much like drought’s seemingly never-ending grip on Nebraska, Stepanek said hypoxylon canker isn’t being picky about limiting its reach. From information collected so far by the Nebraska Forest Service office, drought-related bur oak die-offs seem to be hitting a number of forested areas and urban areas across Nebraska’s eastern side. While oaks are most commonly affected, other popular Nebraska tree species are susceptible as well.

Several trees that line Lincoln’s popular Rock Island trail show hypoxylon canker symptoms: sparse leaf growth and yellowing leaves along the outer edges of the trees’ canopies. (Photo by Jackie Ourada/Nebraska Public Media)

Adam Klingenberg, who’s spent years up in some of Lincoln’s tallest trees as a city forester, is used to seeing deadly tree diseases, but even he was alarmed at how quickly Lincoln’s aging forest is dying due to drought stress. He remembers hypoxylon canker first appearing as far back as 2019.

“I remember cutting into these trees and when you’d cut into it – how dry it was inside there, and just dusty,” Klingenberg recalled. “Every now and then we would see it in a branch or two, a little smaller on some removals. But it wasn’t as concentrated as it is now throughout the whole city. I mean, it’s not just spots throughout Lincoln. Hypoxylon is everywhere.”

Klingenberg estimates Lincoln has around 18,000 oak trees in city rights of way, either in public areas or lining along Lincoln’s roads. Many more shade Lincoln homes from property owners’ yards. So far, hundreds have been taken down due to hypoxylon canker running rampant.

And as Klingenberg stands along a residential intersection near 33rd and South streets in central Lincoln, he can point out a handful of infected trees that will probably need to come down within the next few years. He said dying trees can be spotted along most of Lincoln’s busiest roadways.

Hypoxylon canker overtook several trees in a neighborhood near 33rd and South streets in Lincoln. City crews notified several homeowners in this area that more hypoxylon canker-ridden trees in the city rights of way, including this large oak sitting on a corner lot, will need to be removed soon. The tree is displaying several signs of hypoxylon canker: yellower leaves in the top canopy, dieback on the branches’ ends, and chunks of bark falling off the trunk. (Photo by Jackie Ourada/Nebraska Public Media)

“The hardest part for me is – going to a homeowner, representing the city – how hard it is to tell them, ‘Hey, your tree that doesn't look horrible… is horrible,’” Klingenberg said. “It’s an emotional reaction. Some say, ‘I bought the house because of this tree,’ or ‘This tree has been here the whole time I’ve been here.’”

The drastic drop in tree health comes as a double-whammy when the city is still in the thick of removing ash trees from the emerald ash borer that swept in, in 2016. City and contractor crews have removed thousands of ash trees in Lincoln since then, and with the additional oaks dying from drought stress, the city’s extensive tree canopy could start seeing larger pockets of sun. Klingenberg said that could add to the city’s heat island effect, where the urban sprawl and the lack of trees can magnify the sun’s heat.

He encourages residents who have had to remove their trees to consider replanting using the city’s voucher program. It’s a hopeful measure to offer after the difficult conversations with some homeowners who suddenly lost their trees to hypoxylon canker. The die-off is happening quicker than the city can replant trees, but crews are shooting to diversify the types of trees around the city streets in hopes diseases and bugs won’t spread as easily in the future.

Several drought-stressed trees surround a sign in Nebraska City’s Arbor Lodge State Park. The sign reads, “A tree can be a time machine.” (Photo by Jackie Ourada/Nebraska Public Media)

A similar experiment is happening in Nebraska City, known as the “Tree City of the World,” where the arborists are trying to rebuild canopy cover amid the drought-induced die-offs.

Standing in the town’s Arbor Lodge State Park, Rob Schreiner said he wants to retain the diverse group of trees that attract visitors from across the state.

“Any tree that you want in the state of Nebraska is probably in this park somewhere,” Schreiner said. “We've got them all.”

Schreiner knows just about every tree that’s sprouted here in his hometown. He runs the tree crew for the city’s utilities department and chairs Nebraska City’s tree board. After seeing a number of diseases, bugs and now drought take out several different kinds of Nebraska City’s trees, including ones in his own yard, he’s hoping the newer species he’s planting can better withstand today’s weather.

“I’m doing a lot of experiments now with the Japanese maples,” Schreiner said. “We’re 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 doing well. They’ve built a better tree, basically. They’ve gotten rid of some of the bad characteristics, and they seem to be doing really well.”

For the remaining, surviving trees, Schreiner said he’s taking more measures to ensure they stay perched over Nebraska City’s parks for a few more generations to enjoy.

“With these dry conditions, I tell people right now – yeah, water the trees. It’s not going to hurt them,” Schreiner said. “Normally, for years, I’d say, ‘Once you get it planted and it’s established, you don’t need to water.’ Now, I’m changing my tune. Just like that sycamore over there – a little bit of water on that wouldn’t hurt it at all.”

Nebraska’s forested future remains uncertain

The Nebraska Game and Parks horticulturists have several thoughts about what’s next for one of the state’s most popular parks, but it’s still difficult to picture what this land will look like after more large bur oaks are cleared away this winter. And they admit it’s an unfamiliar feeling to not know what’s in store for this area of Nebraska.

“We are getting to see a pretty significant reset to a climaxing system in our own time,” Whemeyer said. “It’s affecting spaces that we were very comfortable with them having stayed the way they were for a very long period of time. It's an adjustment for everybody, not just the folks working on the land, but the folks that come and visit and enjoy it.”

Nebraska Game and Parks Commission horticulturists Richard Whemeyer (left) and Noah Sundberg survey one of the areas worst-hit by hypoxylon canker at Mahoney State Park. What used to be an area surrounded by leafy trees is now pocked by dozens of brown pits where big bur oak trees stood. (Photo by Jackie Ourada/Nebraska Public Media)

They didn’t expect to see such a steep downfall for the “Titan-esque” bur oaks, as Whemeyer called them. Though it could have been a long time coming, it’s hard to believe that so many have been lost within such a short amount of time.

“Oak trees grow at a pretty slow pace,” Sundberg said. “That's what makes them so resilient to a lot of change, but we're seeing change at such an accelerated rate that they can't adapt as readily. These 150- to 200-year-old oak trees that have been here and have seen so much over the last 200 years just can't handle the conditions of today.”

Sundberg and Whemeyer, who both know these fields like their own backyards, believe these oaks didn’t go down without a hefty fight, and their stories may not be completely over. A few months after clearing 75 trees, Sundberg noticed a few resprouts starting from several stumps – sowing some hope that the mighty native Nebraska oaks might one day return.

A tree stump sits near the edge of Mahoney State Park in June 2025. (Photo by Jackie Ourada/Nebraska Public Media)