You came across a tree with long palm-like tropical leaves. What is it? In New England, it is mostly likely to be ailanthus, sumac, walnut or ash. Ailanthus (Ailanthus altissima), the Tree of Heaven, Asia, and Brooklyn is often considered by naturalists and homeowners alike to be a menace to society with little redeeming value for wildlife. In contrast, smooth sumac (Rhus glabra) and staghorn sumac (Rhus tyhina) are great native Americans, as useful to humans as to our smaller residents. The black walnut (Juglans nigra), another great American, is cultivated in the wild by squirrels who adore these tall, graceful hardwoods, perhaps even more than humans do. The ailanthus is from the Quassia family of tropical plants, the sumacs are cashew family, and the black walnut comes from the walnut family which includes hickories and pecans. Our wonderful native ash trees are olive family members so can be distinguished from the others by the oppositely arranged branches and leaf stalks.

The ailanthus, sumacs, ashes, and black walnut come from totally different families and backgrounds, but can you tell them apart? All have long, palm-like compound leaves but there are major differences in flower, fruit, bark, bud, and leaf shape. This article covers the ailanthus and the sumacs. The black walnut is the subject of Issue 149 (January 30, 2005). Some of the ash trees are pictured in Issue 138 (November 14, 2004)

AILANTHUS: Graceful, tropical-looking ailanthus is the tree that grows in Brooklyn, and just about everywhere else (including Africa and Australia). It is as much a part of the urban landscape as the Norway rat, the cockroach, and the feral cat. Ailanthus was featured in “A Tree Grows in Brooklyn” where this arboreal immigrant’s determination to survive and flourish despite all odds gave inspiration to immigrants of the human species. In Brooklyn, I once saw a ghostly ailanthus sapling growing out of the dirt floor in a lightless sub-basement. Ailanthus saplings waving from roof gutters and fire escapes are common inner-city sights.

As a long-time Brooklyn resident, I have a unreasonable fondness for my old neighbor, the “Tree of Heaven”, as it is known in its native China. In China, the mature trees are valued as ornamentals; and the tree is used for lumber, firewood, medicine, and silkworm farming. (The wood, by the way, is similar to ash in look and quality, and actually is quite useful.) Conversely, in Virginia, where it threatens new forests, ailanthus is known, appropriately, I think, as “stink-tree”.

Unfortunately, like many back-alley denizens, ailanthus is “armed and dangerous”. Ailanthus uses its wind- and water-borne winged seeds (“samaras”) to spread into surrounding neighborhoods. Once it gets established, it spreads into a grove by means of underground shoots. Ailanthus is a proven alleopath; it uses chemical warfare to control its turf. The chemicals it makes can ward off at least 70 other species that could compete with it for space.

Ailanthus, however, can not tolerate deep shade, so despite its chemical armaments, it can’t compete under the thick forest canopy. Instead, ailanthus tends to grow in the sub/urban environment where few trees can compete with ailanthus for ability to withstand urban pollution. Ailanthus can also out-compete native trees when the forest canopy has been disturbed by logging or fire, and it can gain a foot-hold at the forest’s edge by out-competing and poisoning other “pioneer” and edge-of-forest plants. According to the US Forest Service, in China, ailanthus only grows “in a densely populated area of China where no wild lands are left.” Chilling thought.

Ailanthus was first imported into North America, they say, in the 1700’s, and was widely planted in cities (on purpose!) because it was pollution-hardy. Today, ailanthus is found in this hemisphere, in Zones 4 to 8, from Argentina to Canada. In the USA, it is found everywhere except the really cold places such as Alaska, Idaho, the Dakotas, and Minnesota. Ailanthus is useful for ground stabilization in pollution-prone industrial sites but I doubt anyone has to take the time to plant it.

Ailanthus is a fast, fast growing tree that lives only 25 to 50 years but it can get very large – 60 to 100 feet–in that time. While the individual trees aren’t that long lived for trees, the ailanthus groves can sustain themselves for hundreds of years.

Most American wildlife hasn’t much use for the foreign-born ailanthus. Even white tail deer and grey squirrels aren’t partial to it. A couple of bugs of Asian origin, such as Japanese beetles, munch on it (and presumably provide some value to the ecology when the bugs are then munched in turn by birds and small animals). Honeybees (a European import themselves), though, do relish the pollen which makes quality honey after it has been aged.

Ailanthus is weedy and aggressive; it should be controlled for the sake of the environment. In particular, the female plants which send out the seeds should be kept cut to the ground. Further, the trees are not desirable around human dwellings. Larger trees can be a winter/wind hazard and the water-seeking roots have been known to interfere with sewer lines and wells. The roots are also said to give water an unpleasant taste. The males flowers have a strong odor often considered disagreeable (hence the name “stink-tree”). Ailanthus sap can cause dermatitis and the tree is a 9 out of 10 on the bad-for-allergies scale.