Tree Notes is about trees -- especially native trees, trees for wildlife, and trees in history.

Thursday, May 10, 2007

Four trees to avoid

Invasive trees threaten urban forests and native woodlands.


In today's Leaf Chronicle, Jeremy Meyer, city forester of Clarksville, TN, writes about invasive trees that are pushing out native species.

Meyer cites four trees as dangerously invasive in the Clarksville, TN, area. (This area includes my home, Christian County, KY, just across the state line). Meyer points out that these trees have brittle wood and are highly susceptible to weather damage, in addition to being invasive.

  • Bradford Pear -- Pyrus calleryana 'Bradford'
  • Empress Tree -- Paulownia tomentosa
  • Tree of Heaven -- Ailanthus altissima
  • White Poplar and Lombardy Poplar -- Populus alba and Populus nigra


I was alarmed at Meyer's statement that he has seen Bradford Pear establishing itself in woodlands along Interstate 24. It would be a great loss if even one native oak, hickory, ash, maple, etc., is choked out by a Bradford Pear.


I have previously said that you should be aware of a high likelihood of problems and early death with Bradford Pears, but plant it if you must. I hereby retract that statement and urge you to avoid the tree.

This is part one in a series by Meyer that will list a dozen invasive trees. I am sure that the mimosa tree will be featured in one of the future columns. It is a weed tree in this area. It's extremely prolific, and it's hard to kill, once established. Its beauty does not make up for the problems it causes. I have one in my yard, so I know what I'm talking about.

At right: Bradford pear in bloom. Image courtesy of http://www.flickr.com/photos/minidriver/ / CC BY 2.0

10 comments -- please add yours:

Collagemama said...

Please keep me posted on the invasive trees. I've been on a recent kick about three on my block--those darn mimosas, chinaberry, and Arizona ash.

I'm not positive that the "trash tree" down the block is an Arizona ash because it has rough bark. The seeds and leaves and annoyance match the fiendish "trash tree", though.

I've also seen the results of a fire caused by cottonwood fluff on an outdoor air conditioning unit. Folks need to be aware how flammable it is, and keep their a/c units clean.

I've always had allergy problems around sycamore trees. If you have a sycamore, you MUST rake. When the leaves stay on the ground over the winter, they become home to nasty molds.

Genevieve said...

I am not familiar with the Arizona ash, so I looked it up and read that it is fast-growing, withstands heat and drought, produces a lot of seed, and is native to Texas. I can imagine how it might become a problem tree.

That's good advice about sycamore leaves. They probably don't biodegrade quickly because of their large size and general toughness. You'll like this as an art teacher -- sycamore leaves can be used as a canvas for painting!

Oak Leaf said...

Some other trash trees to add to the list, Siberian Elm, Amur Maple, Russian Olive and Buckthorn. Buckthorn is now illegal here in Minnesota, but it is not illegal in all states.

Russian Olive is a threat to river side ecosystems. It has a nitrogen fixing taproot and it makes the soil around it arid.

Bradford Pear smells like Play Doh. Not only that it is notoriously short lived tree.

Anonymous said...

Hear, hear, I agree. Funny that the ads posted by Google at the bottom of your post are advertising the Paulownia as "perfect for your area" and "hardy." They are a beautiful tree, as advertised, but the outward appearance of a few flowers cannot cancel the inherent weak wood, susceptibility to storm damage and invasiveness.

Royal Empress said...

If these trees do so well in your area could they not just as easily be native trees? If a majestic tree like the empress tree takes over, I really dont see the issue.

Genevieve said...

Royal Empress, I republished your comment without the link to your website because I don't provide free advertisements on this blog.

When invasive species -- like the Royal Empress trees you are trying to sell -- crowd out native species, it decreases biodiversity.

Perhaps you don't understand "why biodiversity is important"? You should read about it.

Sequoia said...

The Empress tree is one of those that just takes over and soon that the only tree you'll have. I prefer to have my native species in my backyard.

Anonymous said...

One lovely thing about empress trees is that they are nitrogen fixing. This means they are a fabulous choice to begin food forests as they can be a beautiful and highly efficient "sacrificial tree" to nurse your long term tree of choice. There is a place for everything if you take the time to understand their benefits and uses...

Felix Nuts Tomcat said...

I removed a dead Russian Olive from my front yard last year. I replaced the tree with a native Burr Oak. The tree is growing very fast as it feeds off the rotting roots of the Russian Olive.

Genevieve Netz said...

There is probably a good place for the Empress tree in its native ecosystem. Here, as an exotic tree, it tends to reproduce too freely.

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Print references I frequently consult

Benvie, Sam. Encyclopedia of North American Trees. Buffalo, NY: Firefly, 2000.

Brockman, C. Frank. Trees of North America: A Guide to Field Identification. Ed. Herbert S. Zim. New York: Golden, 1986.

Cliburn, Jerry, and Ginny Clomps. A Key to Missouri Trees in Winter: An Identification Guide. Conservation Commission of the State of Missouri, 1980.

Collingwood, G. H., Warren David Brush, and Devereux Butcher. Knowing Your Trees. Washington: American Forestry Association, 1978.

Dirr, Michael. Dirr's Hardy Trees and Shrubs: an Illustrated Encyclopedia. Portland, Or.: Timber, 1997.

Elias, Thomas S. The Complete Trees of North America; Field Guide and Natural History. New York: Book Division, Times Mirror Magazines, 1980.

Grimm, William Carey. The Book of Trees;. Harrisburg, PA: Stackpole, 1962.

Hightshoe, Gary L. Native Trees, Shrubs, and Vines for Urban and Rural America: a Planting Design Manual for Environmental Designers. New York: Van Nostrand Reinhold, 1988.

Little, Elbert L. National Audubon Society Field Guide to North American Trees. New York: Chanticleer, 1996.

Martin, Alexander C., Herbert S. Zim, and Arnold L. Nelson. American Wildlife and Plants. New York: McGraw Hill, 1951.

Mitchell, Alan F., and David More. The Trees of North America. New York, NY: Facts On File Publications, 1987.

Randall, Charles E. Enjoying Our Trees. Washington: American Forestry Association, 1969.

Settergren, Carl D., and R. E. McDermott. Trees of Missouri. Columbia: University Extension, 1995.

Sternberg, Guy, and James W. Wilson. Native Trees for North American Landscapes: from the Atlantic to the Rockies. Portland: Timber, 2004.

Wharton, Mary E., and Roger W. Barbour. Trees and Shrubs of Kentucky. Lexington: University of Kentucky, 1973.

Wyman, Donald. Trees for American Gardens. New York: Macmillan, 1965.

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