Red Cedar Invasion

What are those pesky evergreen trees popping up in large numbers all over your pasture?

Most likely they are eastern red cedar trees, the only evergreen native to Kansas.

Is the Eastern Red Cedar Invasive?

You may be wondering how a native tree can be invasive. The U.S. Fish & Wildlife Service provides the following definition of an invasive species:

An “invasive species” is defined as a species that is

non-native (or alien) to the ecosystem under consideration and

whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

First we must consider the nonnative aspect. Although the eastern red cedar is native to Kansas, its range has expanded to include ecosystems where it is not native. Cedar trees were formerly restricted to steep, rocky places where fires were uncommon. Now they have expanded across the prairies of the Flint Hills and Red Hills, and have even crept into the Cross Timbers of the Chautauqua Hills. In Riley County alone, cedar coverage increased by 382% in 21 years!

The second criterion was “causes or is likely to cause economic or environmental harm or harm to human health.” The eastern red cedar definitely fits this description in a number of ways.

Economic Harm:

Costs millions of dollars in forage production loss annually.
Draws countless gallons of water annually from nearby streams.
Intercepts 40% to 79% of the rainfall that passes by.
Reduces soil fertility by depleting nitrogen and altering soil pH.
Spreads cedar-apple rust, a disease that affects apple trees.
May cause abortions and low birth weights in sheep and cattle.

Environmental Harm:

Produces toxic oils that kill other native plants.
Destroys the habitat of birds native to open prairie ecosystems.

Harm to Human Health:

Increases risk of dangerous fires in populated areas.
Causes seasonal allergies.

How Cedar Gets a Foothold

So how did the eastern red cedar get so out of control? Cedar trees are opportunists—ecologists call them pioneer species. Pioneer plants are the first species to move into disturbed or damaged soil, quickly putting down roots and shading the ground to prevent further erosion. Obviously, then, pioneer species such as red cedars serve a useful purpose in nature.

But something seems to have changed in the last couple hundred years. Nature must have managed the eastern red cedar a little differently than we do now.

Historical Eastern Red Cedar Management

Historically, there were two tools used to manage the native prairies:

Fire.
Bison herds.

The bison trampled baby cedars and rubbed their horns on the larger trees, keeping them in check. Furthermore, the bison also aided the health of the soil and native grasses by providing fertilizer. Thus grazing was both a proactive and a reactive strategy.

But since some erosion is bound to happen every now and again, fires occasionally swept the prairies clean so that the bison could start over.

Modern Eastern Red Cedar Management

Today, ranchers have access to four tools for controlling invasions:

Fire.
Cutting.
Chemicals.
Livestock.

Fire is a very familiar tool to those who live in the Flint Hills. Many ranchers rely exclusively on prescribed burns to keep their pastures free of trees.

Cutting is now an option with modern equipment, and is sometimes the best bet for larger trees. Unfortunately, cutting cedar trees can sometimes disturb the soil, which will invite more pioneers onto the scene.

A variety of chemicals are available that work on eastern red cedar trees. Needless to say, these herbicides often pose a risk to the surrounding noncedar plants.

One tool that is all too frequently forgotten is livestock. Grazing pressure still works well on eastern red cedars. Of course, overgrazing will erode the land and create a new invasion problem, but skillfully managed grazing has a very beneficial impact on pastures.

So even though the eastern red cedar problem has exploded in recent years, there is still hope. With a little care, the beautiful native prairies of Kansas can remain intact.

Helpful Resources

Eastern Red-cedar: Positives, Negatives and Mangement
Excellent 8-page PDF download that explores the history of cedar expansion, the pros and cons of cedar trees, and different management techniques.

Lessons from the Bison
In case you wanted to learn more about nature’s way of managing tallgrass prairie.

What is Management-Intensive Grazing?
A starting point for further research on using animals to manage pastures.