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

Three Fast Growing Trees with Problems

Think twice before planting these trees!

As America gears up for the spring planting season, stores and nurseries across the nation will stock millions of trees. Some of them will be labeled, "Fast growing," and those are words that bring joy to the hearts of tree-planters. Be careful! Here are three fast-growing trees that you may regret planting.

1. Bradford Pear/Pyrus calleryana 'Bradford'

Bradford Pear image by Britt Slattery,
US Fish and Wildlife Service.

This tree is beautiful in three seasons --  spring, summer, and fall. It has abundant white blossoms early in spring, and its shiny green foliage turns red in autumn.

In winter, the Bradford Pear is not so attractive because its broken parts are no longer hidden by its leaves. And this tree does typically have a lot of broken parts. The dense branching, narrow branch crotches and weak wood cause it to break in wind, snow, ice -- and even heavy rain!

I have personally seen dozens of Bradford Pears severely damaged by weather events. Often the whole tree splits apart and an entire quarter or half of the tree tears away and falls to the ground.

If the tree lasts more than ten years without a disfiguring loss of branches or a partially dead crown, count yourself lucky. Bradford pears are very short-lived (30 years, max.)

2. Mimosa Tree/Albizia julibrissin

Wikimedia image by Simon Garbutt (SiGarb)

Mimosa trees (also called silk trees) have fragrant pink blossoms in summer, and their lacy foliage and multi-stemmed growth has a tropical look. It is a very fast-growing tree (3 feet or more per year.)

Mimosas grow all over the southeastern United States, where they have naturalized after being introduced as an ornamental in 1745. They are an invasive species; that is, they reproduce so freely and rapidly in the wild that they displace native species. That alone is good reason not to plant them. Mimosa seedlings and suckers will invade any part of your yard that's not regularly mowed and any flower bed that's not frequently weeded. They will also invade your neighbor's yard and flower beds!

 Besides being extremely invasive, the mimosa is a problem tree because of its weak, brittle wood which often breaks in storms.  It is vulnerable to a number of insects, and it is very short lived (15 to 20 years.)

3. Lombardy Poplar (Populus nigra)

Lombardy poplars grow very fast indeed, and their narrow columnar shape makes them desirable for tight spaces. However, they are weak-wooded and very short-lived due to their susceptibility to disease. They send up suckers from their roots in a hundred-foot circle or more. Their rooting system includes extensive surface roots which can make mowing difficult.

Even the "hybrid poplars" that are touted to have a longer lifespan will die young. We planted ten hybrid poplars about 15 years ago, and three have already died. In retrospect, we regret planting them, even though they served their purpose effectively for a few years as a screen from the road.

An interesting history of the Lombardy poplar (pdf) 

Flikr image by wallygrom