September Tree of the Month: TREE OF HEAVEN

Tree of Heaven (Ailanthus Altissimus)
by Martin (Mort) Schmidt for Simply Living

Left – Leaflets. Right – Compound leaves.
Photos by Mort Schmidt.
Left – Leaf Scars. Right – Bark. Photos by Mort Schmidt.
Left – Seeds. Right – Chambered pith in walnut. Photos by Mort Schmidt.
Spotted lanternfly. Photo by Pennsylvania Department of Agriculture.

The latest Tree of the Month is a bad seed, if you’ll pardon the expression. If you’re someone who’s drawn to exotic beauties who are known troublemakers, Ailanthus altissima is the tree for you.
Tree of heaven is native to China, and due to its hardiness, and in the eyes of many, it’s exotic beauty, it’s been naturalized worldwide. Like all invasive plants and animals, tree of heaven is perfectly well behaved in its native habitat. But while some species wither and die when they’re transplanted away from home, others go wild in the absence of competition and adversaries. Because of its hardiness and adaptability, this tree is often found on abandoned or neglected properties, growing up through drains and cracks in pavement.
Tree of heaven has alternate, pinnately compound leaves, with 13 to 41 leaflets. (Pinnately compound leaves have leaflets attached to the stem at multiple points, whereas palmately compound leaves have leaflets attached at a single point, like the fingers in the palm of your hand). Leaflets are several inches long, have no lobes, and have smooth edges except for several teeth near the stem. The leaflets have a disagreeable odor when crushed – hence the other common name, stink tree. The compound leaf is the largest of any found in Ohio, often several feet in length. Notice in the photograph that the compound leaf is longer than my torso! Because the compound leaf is so large, it leaves a huge scar when it falls off late in autumn. The horseshoe or heart-shaped scars are often larger than a quarter.
Ailanthus can grow to a height of 80 ft with a trunk diameter up to 3 ft. Also owing to the immense leaf size, the twigs are unusually stout – typically the diameter of your pinky or thumb. The bark on twigs and saplings is light brown and smooth, but becomes light gray and fissured on larger trees. Seeds typically appear on female trees in late summer and fall, and consist of twisted, reddish, 1.5″ samaras (wafers) with one seed. Large trees with seeds are recognizable from a distance by their reddish color.
Sumacs can be distinguished from tree of heaven by their toothed leaflets, agreeable odor, and berry-like fruits. Tree of heaven also resembles walnut, but a lengthwise slice in a walnut twig reveals chambered pith.
According to Wood-Database.com, Ailanthus provides potentially useful lumber. It’s moderately hard, with a dry density of 0.60 g/cc, on par with white ash. It works well, readily takes stains and glues, and can be planed or sanded to a fine luster. Unfortunately, sensitive people are allergic to its dust and leaves. It’s toxic properties are no doubt responsible for its natural resistance to insects.
According to the book Leaves in Myth, Magic & Medicine, tree of heaven was brought to from China to Europe to feed a species of silkworm, when disease threatened the silkworms that fed on mulberry leaves. Ailanthus silk is tougher and cheaper than mulberry silk, but coarser and less glossy. An extraction of the leaves and bark was also ingested to drive out tapeworms.
The main problem with tree of heaven is that it also drives out native plants, due to its hardiness and its allelopathy – the production of chemicals that harm surrounding plants. Ailanthus also serves as a harbor for the invasive spotted lanternfly. This moth has piercing mouth parts that enable it to aggressively suck large volumes of sap from maples, walnuts, and other valuable trees. The lanternfly also exudes large volumes of a sticky, sugary substance that grows harmful fungus and attracts wasps. The lanternfly is poisonous to many predators, and it’s suspected of extracting its toxin from the tree of heaven. Tree of heaven should be replaced with native trees, or simply removed. But, who knows? If we continue to destroy native trees with invasive pests, such as emerald ash borer and spotted lanternflies, we might be glad to have any trees at all!