The Mystery of the Dying Cedar Trees

As I travel across Nebraska this year, I keep seeing dead and dying eastern red cedar trees.  Some are big, some are small, but they’re definitely dead.  Since cedar trees are a major invader of grasslands across the state, I’m not complaining about all the dead ones, but I do wonder what’s killing them.

Why are cedar trees dying around Nebraska?

Why are cedar trees like these dying around Nebraska?

Interestingly, the trees seem to be dying in clusters, rather than as random or scattered individuals.  To me, that indicates at least two possible causes of death.  One possibility is that some kind of disease or insect is killing trees and then spreading to others nearby.  The second is that trees are dying from last year’s drought conditions and that local variation in soil texture means that cedars in some places were more vulnerable to drought than others.


Not all cedar trees are dying.  Sometimes it appears that random trees are dying and others right next to them are not.  Upon closer inspection, however, there are usually clusters of trees that are dying (note the right side of this photo).  Disease?  Or drought/soils?

Since my experience with trees is mostly limited to attempts to keep them out of my prairies, I thought I’d contact someone who has a broader range of expertise on the subject.  I emailed Scott Josiah, the state forester with the Nebraska Forest Service and asked him why cedar trees are dying.  Scott said he thought the drought hypothesis made the most sense, and that trees growing in soils with coarse sands and low levels of organic matter, for example, would be stressed more than those in soils that hold more moisture.

It was good to hear from an expert on the subject, but I’ll admit to a little skepticism.  I really like Scott, and as I said above, I’m no expert on trees, but cedar trees sure seem like they’d be tough enough to survive a one year drought…  Heck, I’ve seen them growing out of ROCKS!  I took Scott’s answer and filed it away, but continued to wonder about the possibility of a disease or insect outbreak that foresters and others just hadn’t yet identified.

And then last week, I found some pretty convincing evidence that I think has solved the mystery.

We were at our Kelly Tract on the North Platte River, working on some vegetation sampling and Canada thistle control when I noticed some dead cedar trees in some old shelterbelts on the property.  As I got closer, I realized this was a perfect site to test Scott’s idea that drought was killing cedar trees.  The Kelly Tract is a floodplain prairie with strong patterns of alluvial (river deposited) soils across the site.  That means there are lots of different soil types all mixed together – a naturally-occurring experimental design.

soil patterns

From this angle, you can clearly see some of the alluvial soil patterns that intersect with the line of cedar trees at The Nature Conservancy’s Kelly Tract along the North Platte River by Sutherland, Nebraska.

While conducting my vegetation surveys, I noticed that last year’s drought had definitely affected the grasses and wildflowers much more severely in some places than others.  Broad streaks of green and brown wound across the prairie, tracing the old channels and sandbars formed when the river had long ago flowed across the site.  When we’ve done soil sampling elsewhere along the Platte, we’ve found that soils with coarse sand and low organic matter are quickest to dry up in drought conditions – I assume the same is true at the Kelly Tract.  I figured that if drought, combined with soil texture, was killing cedar trees, I’d be able to see whether the dead trees were in the same “streaks” that contained dried up grasses and wildflowers.

They were.  In fact, every brown tree I saw was located along a streak of brown grass, and every green tree was in a streak of green grass.  It was as perfect a pattern as you could hope for.

The outlined area in this aerial photo.

This aerial photo from several years ago shows the alluvial soil patterns more clearly than in the earlier photo.  The red outline is approximately the same location the earlier photo was taken from.  I haven’t yet been able to find any aerial photography from this year (this older photo doesn’t show this year’s brown trees) but when I do, I’ll bet the brown trees will be in the brown streaks…

While cedar trees are certainly tough, it sure looks as if Scott was right – last year’s drought was just too much for those trees to handle, at least in some soils.  Mystery solved!

Way to go, Scott!   Now I have a new problem…  Do I hope for a wet year to help our prairies recover?  Or a dry year to kill more cedars??

Restoring Cottonwoods to the Missouri River (Part 2)

Back in February I wrote a short post about our cottonwood tree planting efforts on the Missouri River.  Here’s a more detailed description of that project, including some early (and interesting) results.

Tyler Janke, our Missouri River restoration ecologist, holds a young cottonwood seedling from our demonstration project’s first season.

The project started as some informal discussions with Scott Josiah, the state forester for the Nebraska Forest Service.   I mentioned to Scott my concerns that most of our cottonwood woodlands on Nebraska’s big rivers consist primarily of mature trees, and that we aren’t seeing many new cottonwood stands becoming established.  As existing cottonwood trees die of old age, they’ll be replaced by the trees that are now filling the understory of the woodlands, including species such as ash, mulberry, hackberry, and eastern redcedar.  Those are all fine trees, but provide a very different kind of habitat than a cottonwood woodland.  Scott was interested in the same issue and, a few months later, approached me with an opportunity to join them on a grant application to fund a collaborative project.

We successfully obtained a grant from the U.S. Forest Service for a three year demonstration project, and the National Arbor Day Foundation jumped in with additional funding and support.  Tyler Janke, our restoration ecologist along the Missouri River is spearheading the project, and will be restoring approximately 300 acres of cottonwood woodland over the next three years.  Along the way, we’ll be trying and comparing a number of techniques to figure out what works best, including:

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