Some of the most common and troubling invasive species and what to do with them.

When fire is suppressed and herbivores are absent, a prairie will fairly quickly accumulate a variety of plants — mostly shrubs and trees — that will quickly degrade the quality of the prairie. Some of these invasives are nonnative introduced plants, but others are natives that are simply aggressively weedy when no longer constrained by natural means. Here are the invasives that we spend most of our time dealing with, and what we do about them.

Red Cedar

Eastern red cedar is a prolific native evergreen tree in Kansas. Female trees produces berries that are popular with birds — with the side-effect of this beneficial feature being that seedlings pop up everywhere. Left alone, a field will soon be crowded with large cedar trees that obliterate all other plants beneath them and shade and inhibit plants between them. Such former prairies are all too evident.

Regular prescribed burns will kill small seedlings and keep a remnant clear, but fire will not kill trees that are more than a year or two old. These larger cedars must be cut. If caught at this stage, a hand lopper works well, but once they’re several years old, a hand saw is required. When even older trees are present, it’s time for the chain saw. Since cedars produce a large volume of branches, brush removal is tedious and difficult, and most people promptly burn the debris. The good news about cedar is that once cut, the tree dies; there is no need to treat the stump with herbicide.

Because red cedar also provides good cover, there is some debate as to whether to extirpate them from a property or simply control them. One approach we’ve taken is to remove the female trees to reduce the number of new seedlings and leave the the male trees for nesting. Other people declare that the only good cedar is a dead cedar. One thing is certain: even if you remove all the cedars on your property, you can be confident that there will be plenty left in adjacent properties. The birds will be able to find sustenance somewhere.

Smooth Sumac

Smooth Sumac is another prolific native shrub that also produces lots of bird-friendly berries. It also is very attractive, particularly in the fall when its leaves turn a brilliant red. However, in addition to its aggressive propagation by seeds, smooth sumac grows rhizomatously and forms colonies in the same fashion as aspens — the result being that a given prairie can quickly become infested with wall-to-wall sumac. The sumac shade the ground and select for cool-season grasses and inhibit forbs — so any prairie needs to be controlled aggressively for sumac if it’s to retain high quality.

Unfortunately, sumac is tough to manage. Burning doesn’t kill it, and cutting (by hand or by mowing) merely seems to make it mad. Herbicides appear to be the only effective approach, and we spot-spray individual sumacs by hand with a foliar application during spring and summer. With careful reapplication, even nasty smooth sumac infestations can be controlled in a couple of seasons.

Sericea Lespedeza

Sericea lespedeza (Lespedeza cuneata) is actually the worst offender in this list. It lacks the thorns of some of the others, but it produces vast amounts of seed that remains viable for decades, so it can quickly convert a happy prairie into a nasty monoculture. Thousands of acres are infested in Kansas, and it is an official noxious weed that you are obligated to remove.

The only viable approach is herbicides. Mowing and burning merely amuse sericea. Careful repeat application is necessary because the heavy seed burden in the soil guarantees new seedings for years. Once you have a few plants, you’ll continue to have them, so infested areas must be tracked consistently and aggressively.

Osage Orange

Osage orange (Maclura pomifera) aka “hedge” is another native tree that doesn’t respect its neighbors. Planted extensively for windbreaks and property boundaries, the tree proliferates far beyond where you would expect to find its “hedge apples” — indicating that friendly birds are helping it along. The good news is that osage orange doesn’t form colonies, but the bad news is that it grows happily and produces nasty thorns. It doesn’t create quite the species-altering shade problems, but it will jeopardize the health and safety of you as you walk your prairie.

Osage oranges in the wrong place simply need to be cut, and the stumps need to be treated with herbicide, or else they’ll simply be back with a vengeance next year.

Honey Locust

Honey Locust (Gleditsia triacanthos) is another native tree that just doesn’t know when to quit. It also spreads rhizomatously to form dense colonies, plus it produces wicked 3-5 inch long thorns that putatively evolved to ward off the mastodons that once helped keep it in check. Locust seeds also appear popular with birds, and small locust trees show up in an prairie — just not as many as cedar, sumac, elm or osage orange (fortunately).

These nasty trees need to be cut promptly and the stumps treated with an appropriate herbicide. Be particularly careful with the debris, as those thorns take a long time to rot and will gleefully puncture tires long after the tree has been forgotten. Remove all debris to a safe location!

Others

We see plenty of small elms here and there; these are far less aggressive and nasty, but they also need to be cut and stump-treated with herbicide.

Created: October 22, 2008 18:13
Last updated: November 10, 2010 15:10

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