Invasive Exotic Trees: Avoid Planting Princess Tree, Tree of Heaven, Paper Mulberry

Not all trees you find in a greenhouse are good for the environment. Take exotic invasive trees — they are known to take over a landscape. Avoid them at all costs.

“Invasive Exotics Take Over!” It could be the title of a science fiction movie. While invasive exotic trees are not out of this world – most are from Asia or Europe – many areas in North America are being threatened by imported trees that have an aggressive and rapid growth rate.

According to Invasive.org, a website dedicated to informing the public about invasive plant life, an exotic invasive is categorized as, “…any species, including its seeds, eggs, spores, or other biological material capable of propagating that species, that is not native to that ecosystem; and whose introduction does or is likely to cause economic or environmental harm or harm to human health.”

Exotic invasive trees comprise a small percentage of the total invasive plant life (which includes aquatic plants, herbs, shrubs and vines) – but what makes them so insidious to our North American woodlands is that they have distinct advantages over native trees.

Invasive Exotic Trees Edge Out Native Species in the Landscape

For example, many invasive exotic trees leaf out before native trees – creating growth-inhibiting shade for the indigenous species and give the exotics a leg up in the growing season.

Since exotic plants do not have the natural controls present in their native lands – such as herbivore animals, parasites and diseases — these exotic plants have an unfair advantage over native species and often go “wild” expanding over large areas, overwhelming existing vegetation and sometimes forming dense one-species stands.

These aggressive invaders also reduce the amount of water, nutrients, light and space for native species and alter the soil chemistry and erodibility.

Some exotic plants can even hybridize with native plant relatives, resulting in unnatural changes to a plant’s genetic makeup; others have been found to harbor plant pathogens. Still others contain toxins that may be poisonous to some native animals. (For example, garlic mustard is lethal to a native butterfly species.)

The Top 10 Exotic Invasive Trees in the U.S.

At last count there were about 4000 species of exotic plants (including trees, herbs, vines and shrubs) in the United States.

About 1000 of these exotic plants are considered invasive and a threat to our native species.

Here are some of the top exotic invasive trees in the U.S.:

#1. Tree-of-Heaven (Ailanthus altissima)

from China (also known as ailanthus, Chinese sumac, and stinking shumac)

#2. Silk Tree (Albizia julibrissin)

from Iran to Japan (Also known as mimosa and silky acacia).

#3. Paper Mulberry (Broussonetia papyrifera)

from Japan and Taiwan

#4. Australian Pine (Casuarina equisetifolia)

from Malaysia, southern Asia, Oceania and Australia (Also known as ironwood, beefwood, she oak and horsetail tree)

#5. Carrotwood (Cupaniopsis anacardioides)

from Australia, Irian Jaya (Indonesia) and Papua New Guinea

#6. Paperback Tree(Melaleuca quinquenervia)

from Australia, New Guinea and New Caledonia (Also known as punk tree, cajeput tree, and white bottlebrush tree)

#7. Princess Tree (Paulownia tomentosa)

from China (Also known as royal paulownia or empress tree)

#8. White Poplar (Populus alba)

from Central and southern Europe to western Siberia and central Asia (Also known as silver-leaved or silverleaf poplar.)

Related: Types of poplar trees

#9. Common buckthorn (Rhamnus cathartica)

from Eurasia

#10. Salt cedar (Tamarix species)

from Eurasia and Africa