Heat, Drought Killing Nebraska's Evergreens

An Austrian pine tree suffering from diplodia blight, exacerbated by drought. (Photo by Ariana Brocious, NET News)
Root stock test plot at University of Nebraska-Lincoln's East Campus. (Photo by Ariana Brocious, NET News)
The Nebraska Statewide Arboretum tests and cultivates different tree and plant species to determine which do best in the state’s variable climate. (Photo by Ariana Brocious, NET News)
Root bags like this one can help trees grow healthier root systems, which will help them establish quickly and catch up to bigger trees in just a few years. (Photo by Ariana Brocious, NET News)
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May 23, 2013 - 6:30am

2012 was a record-setting hot and dry year—and a terrible one for trees. Thousands burned in wildfires, and thousands more were parched across the rest of Nebraska.  

Mark Harrell, forest health program leader with the Nebraska Forest Service, examines a tree just outside his office on the University of Nebraska-Lincoln’s East Campus. This Eastern white pine has several brown branches.

Harrell points to the dried resin on the bark, “That’s a typical symptom of fungus disease affecting branches. Those are very common on trees stressed from drought.”

Harrell said the tree is likely suffering from a fungus or a root disease, and may not survive the summer. Last year’s lack of water severely stressed trees in Nebraska, making them more susceptible to disease and pests—if not killing them outright. It especially hurt evergreen species that aren’t native to the region, and often aren’t adapted to drought. Deciduous trees can often respond better by dropping their leaves when stressed.      

“White pine is not native around here and it really needs more moisture than we have typically. And last year we actually saw quite a few of them die, just because it was so dry,” Harrell said.

"If we don't get rain, we need irrigation," NFS Forest Health Program Leader Mark Harrell said. For drought-stressed trees, he recommends one inch of water over their root area every week, applied all at once or split over a couple waterings. 

The city of Lincoln is seeing this play out. Lincoln Parks and Recreation Director Lynn Johnson said they removed more than 800 street trees last year, 50 percent more than normal. And Johnson said they removed almost the same number at Pioneers Park alone—mostly pine—despite earlier efforts to diversify the tree mix there. But they’re not planning to replace them all. Increasingly, Johnson said they’re using plants that are better able to withstand drought.

“On a proportion share, we’re probably planting less trees in parks than we used to per acre, and much more reliant on native grasses,” Johnson said.

This tree die-off isn’t limited to Lincoln. Communities all across the state are seeing the effects of the drought on their streets, parks and windbreaks.

NFS Northwest District Forester Doak Nickerson said things are significantly worse on the other side of the state.

 “We’re adrift in a really bad situation right now. Trees that are 20 to 30 to 80 to 100 years old are starting to go away. It’s just simply too many years continuous dry,” Nickerson said.

Nickerson said the drought has already been underway for a decade, despite a couple of wet years. But it was accelerated by last year’s record-breaking high temperatures, which helped spark the worst wildfire season in state history. Fires raged across north-central Nebraska and destroyed thousands of acres of the native Pine Ridge Forest near Chadron.

"In the matter of five short decades, we’ve seen our timber land base go from 250,000 acres of live, green viable forest to something less than 100,000 acres, probably more around 80,000 to 90,000 acres left," Northwest District Forester Doak Nickerson said about the Pine Ridge Forest in Northwestern Nebraska.

“After smoke cleared in 2012, we dropped our forestland acreage to about 40 percent of what it was historically. That’s how bad it is. We are literally losing this forest resource right in front of our very eyes,” Nickerson said.  

Wildfires in recent years have effectively reduced Nickerson’s forest management to triage, he said, trying to save the limited remaining stock of native trees from disease and fire so they can eventually repopulate the landscape. But he’s even more worried about the summer ahead—because the subsoil moisture stored from 2010 and 2011 is completely gone.

“Now, it’s talcum powder dry in the subsoil. So our trees are going into growing season with incredible heat. And really all they’re going to have to live on would be what might come from rain in the next four to six weeks,” Nickerson said.   

Eric Berg is Community Forestry Program Leader for the Nebraska Forest Service. The agency works with the Nebraska Statewide Arboretum to determine which tree and plant species do best in the state’s variable climate. Not only is there substantial climate and ecosystem diversity across Nebraska, but big ranges in temperature and moisture within a given year. Back on UNL’s East Campus, Berg shows me around test plots for different kinds of tree root stock.

NFS Community Forestry Program Leader Eric Berg said Nebraska's variable weather, combined with a changing global climate, present a challenge.  "The million dollar question for us--that we don’t know the answer to--is where should our seed source be coming from? Our response is, let’s just plant a whole lot of everything." Diversity is key, he said.

“Was last year normal? Hopefully not. But if we’re going to continue to plant trees, when we put them out in the landscape, they’ve got to establish quickly. So if we start them right with a vigorous root system, they’ll quickly reestablish and be more adept at taking those weather extremes we know are going to happen,” Berg said.

Clearly, this isn’t Nebraska’s first drought. But Berg said they’re still trying to figure out which trees do best. When disease began killing a large number of Australian pines decades ago, many people switched to planting Scotch pine. But then pine wilt swept through and has killed thousands of those trees. Now other evergreens, like white pine, are struggling with the heat and drought.

So what’s the solution? Everyone had the same answer: diversity.

Berg said that’s a fundamental part of creating resilient landscapes. “The more we can keep it native, with proven stock, proven seed sources and adapted stock, we think the better off we’ll be in the long term,” he said.

With more drought and heat projected for the future, moving away from some of the cooler-weather species might be one option. ReTree Nebraska—a collaboration of several forestry, research and environmental partners—has released its annual list of recommended tree species that are well-adapted to grow in Nebraska. This year, only two evergreens made the list.

For more resources on how to care for trees, and which species are recommended for planting in Nebraska, see ReTree Nebraska and the Nebraska Forest Service.

Thursday evening on the UNL East Campus, Justin Evertson of the Nebraska Forest Service will give a presentation on “Trees for a Changing Climate” as part of the Maxwell Arboretum celebration. The event starts at 5:30 PM. More details here.




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