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The Tree of Heaven….is not so Heavenly it seems

If a rose by any other name would smell as sweet, then the opposite must be true when considering some of the less charming plants. I know that it’s unfair to condemn one individual plant, no matter how smelly, allergenic, or uncharismatic it might be. But when that plant has run amuck with great masses of its equally offensive offspring, then fairness must take a back seat to a measured amount of negativity. Such is the case with one of the most successful woody weeds that we have in Arizona. Its botanical name is Ailanthus altissima. The genus Ailanthus  is  a Latin-ized version of an Indonesian word that means “tree of heaven” and the species name altissima is Latin for “very tall”. Rather than complimenting each other, the genus and species mean essentially the same thing, making the two names together only half as meaningful.

The common names that people use for Ailanthus roll off the tongue with such a wide range of meaning that you wonder if they are all looking at the same tree.

The most widely used common name is the “tree of heaven,” but an equally ethereal “paradise tree” runs a close second. To a vocal minority of naysayers, they are known as “cancer trees.” Some really angry people even call them “stinking sumacs,” a particularly ugly name because Ailanthus  isn’t even a sumac.

The difference in this wildly differing point-of-view depends on your definition of the word “success.”

Ailanthus can grow in nearly any kind of soil type or soil pH, reproduces rapidly from as many as a third of a million seeds per tree, forms large masses from root suckers, and prefers disturbed areas in towns and cities as well as the banks of many riparian areas. It is a tree that is now found in 42 states, exploiting opportunities and moving fast, colonizing the dregs of plant habitat. It’s almost as if it had been coached, a halftime pep talk that the tree took a bit too literally.

As far as the tree of heaven is concerned, it has reached the pinnacle of success. It has not only reached vertically towards the heavens, it has crept steadily in a horizontal direction as well, creating its own mono cultural version of paradise.

How did it get here? The first seed was smuggled out of China into England in the mid 18th century and brought to the east coast of the US a few years later. After the tree had gained a substantial foothold in the eastern states, the seed is thought to have been brought to the west coast by Chinese gold miners. Possibly for the same reason, it is strongly associated with mining towns in Arizona. It is the tree that some say is “holding up Jerome,” and it is a dominant tree in the towns of Globe, Miami, and Cottonwood, Arizona, both in residential and native riparian areas.

Once Ailanthus trees invade a new area, they effectively out-compete native species and then, in a showing of what can only be called plant greed, they produce allelopathic chemicals that affectively poison the soil and prevent most other plants from growing near them. Every spring, they repel humans too with copious amounts of wind borne pollen production from flowers that could smell better.

If you try to mow them down with chainsaws, they will return fire by coppicing themselves ten-fold with new shoots that sprout from the stump. It’s like fighting an army of self-replicating robots in a Star Wars epic. The only way to really control them is through the proper timing and repeated application of several very specific herbicides.

In a few last words of defense, Ailanthus can be an attractive and broadly-rounded shade tree that is re-markedly drought tolerant and fast growing. It has yellow fall foliage, produces copious amounts of shade, has a smooth gray bark and, if managed correctly, can make an attractive street tree that rarely suckers once it’s mature.

Despite its short list of positive attributes, it still sits at the lowest level of desirability—to be tolerated at best, but never encouraged.

Reprinted from GMT Spring 2008, regarding the ubiquitous “Tree of Heaven” now seen all over Globe-Miami.

About Kim Stone

Kim Stone was a horticulturist, writer, and editor of several publications for the University of Arizona at Boyce Thompson Arboretum over the better part of three decades. He is now happily self-absorbed in freelance writing, travel, and content marketing.

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