The Tree of Heaven (Ailanthus altissima) is a rapidly growing deciduous tree native to China, introduced to North America in the late 1700s. Initially valued for its hardiness and fast growth as an ornamental shade tree, it has since become a widespread invasive species across the United States. Its aggressive nature causes significant environmental degradation and structural damage in both urban and rural environments. Its tolerance for poor soil and air quality allows it to thrive in disturbed areas like roadsides, railways, and vacant lots.
Mechanisms of Ecological Dominance
The Tree of Heaven aggressively outcompetes native plant life through allelopathy. This involves the tree releasing phytotoxic chemicals into the surrounding soil that inhibit the growth and germination of other plants. The primary compound responsible is Ailanthone, a quassinoid that acts as a natural herbicide.
Ailanthone is concentrated in the tree’s roots and bark, disrupting root elongation and suppressing seed germination of nearby species. This chemical warfare allows the Tree of Heaven to quickly establish dense, nearly monocultural thickets, displacing native species and degrading wildlife habitat. The tree exhibits a rapid growth rate, sometimes up to six feet in a single year, enabling it to quickly overtop and shade out slower-growing competitors.
Beyond chemical dominance, the Tree of Heaven is a prolific reproducer, ensuring its swift spread. A single female tree can produce hundreds of thousands of wind-dispersed seeds annually, contributing to its wide distribution. The tree also regenerates vigorously from its extensive, shallow root system by sending up numerous new shoots, or suckers, that can emerge up to 50 feet away from the parent tree.
Damage to Built Infrastructure
The Tree of Heaven’s aggressive root system threatens human-built structures and utilities, especially in urban settings. Its shallow, strong roots seek out moisture and exploit weaknesses, leading to extensive physical damage. This destruction includes cracking concrete sidewalks, lifting asphalt driveways, and compromising building foundations.
The roots invade underground utility lines, such as sewer and drainage pipes, causing blockages and necessitating costly repairs. As the tree matures, its wood is relatively soft and structurally weak, making it prone to breaking. This weakness creates a risk of falling branches or entire trees during storms, posing a hazard to people and property.
Direct Health and Nuisance Concerns
The Tree of Heaven is a source of nuisance and health issues for people who encounter it. When the leaves, bark, or twigs are crushed, the plant releases a strong, offensive odor often described as rancid peanut butter or rotting nuts. This unpleasant smell is particularly noticeable around the male flowers when they are blooming.
Contact with the plant material can trigger health concerns in sensitive individuals. The sap from the leaves, stems, and seeds is known to cause contact dermatitis, which manifests as a skin irritation or rash. The tree is a high pollen producer, and its wind-borne pollen can cause seasonal allergies in some people.
Facilitation of Invasive Insect Pests
A primary problem caused by the Tree of Heaven is its role as the preferred host plant for the invasive insect, the Spotted Lanternfly (Lycorma delicatula). The presence of the Tree of Heaven is a primary factor in the establishment and spread of the pest across North America. The Spotted Lanternfly requires the Tree of Heaven to complete its life cycle, particularly for adult feeding and reproduction.
The Spotted Lanternfly threatens agricultural industries, feeding on the sap of over 70 plant species, including crops like grapes, hops, apple trees, and stone fruits. While feeding, the insects excrete a sugary waste product called honeydew, which promotes the growth of black sooty mold on plants and surfaces beneath them. Due to this host-pest relationship, managing the Tree of Heaven is considered a strategy in controlling Spotted Lanternfly populations, with some management plans using the tree as a “trap crop” to concentrate and eliminate the insects.