The Tree of Heaven (Ailanthus altissima) is a fast-growing deciduous tree native to East Asia, introduced to the United States in the late 1700s as an ornamental species. Its ability to thrive in poor soils, tolerate pollution, and establish itself quickly in urban environments made it popular for a time. These characteristics, however, have allowed it to spread aggressively across the globe, becoming a highly destructive invasive species that causes widespread environmental and structural damage.
Ecological Displacement and Soil Alteration
The Tree of Heaven aggressively displaces native vegetation by quickly forming dense thickets that block sunlight from reaching the forest floor. Its rapid growth rate, which can reach up to three feet per year, allows it to outcompete slower-growing local species. Furthermore, a single female tree is a prolific seed producer, generating hundreds of thousands of wind-dispersed seeds annually, allowing it to colonize new areas rapidly.
The tree possesses a distinctive biological weapon known as allelopathy, which is the release of chemical compounds that inhibit the growth of surrounding plants. This toxic effect is primarily caused by a chemical called ailanthone, a quassinoid compound found in its roots, bark, and leaves. Ailanthone is particularly effective at suppressing the germination and growth of many native plant species, essentially sterilizing the soil for its competitors.
By introducing this toxic compound into the soil, the tree not only outgrows but also chemically attacks its neighbors, fundamentally altering the local ecosystem. This process leads to the formation of monocultures, where the Tree of Heaven dominates the plant community, drastically reducing native biodiversity. The loss of native plants subsequently degrades the habitat for native insects and wildlife, which rely on specific plant species for food and shelter.
Infrastructure Damage from Root Systems
The Tree of Heaven’s root system is shallow, aggressive, and highly problematic for human-built structures. These roots send out numerous suckers, which can emerge up to 50 feet away from the parent tree. This vegetative spread makes eradication extremely difficult and allows the tree to colonize urban areas rapidly.
The vigorous, fast-spreading root structure is powerful enough to compromise concrete and masonry. It commonly causes cracking and upheaval in sidewalks, driveways, patios, and asphalt roadways. The roots also pose a threat to underground infrastructure, frequently damaging water and sewer lines, leading to costly repairs.
Beyond the subterranean damage, the tree itself presents structural risks due to its weak, brittle wood and fast-growing nature. During storms or high winds, the limbs are prone to breakage, which can cause damage to vehicles, roofs, and other property. This combination of aggressive root growth and structural frailty makes the Tree of Heaven a significant liability for property owners and municipalities.
Hosting Invasive Agricultural Pests
The presence of the Tree of Heaven serves as a biological platform for the spread of other invasive organisms, most notably the Spotted Lanternfly (Lycorma delicatula). This tree is the preferred and primary host for the Spotted Lanternfly, an invasive insect accidentally introduced from Asia. The insect requires the Tree of Heaven for a portion of its life cycle, making the tree’s presence a direct factor in the pest’s establishment and proliferation.
The Spotted Lanternfly is a sap-sucking pest that feeds on over 70 different plant species, but its reliance on the Tree of Heaven allows its populations to multiply and expand their range. Once established, the lanternfly causes extensive damage to valuable agricultural products. High-value crops such as grapes, apples, hops, and various fruit trees are particularly vulnerable to its feeding habits.
The economic damage caused by this pest is substantial, with potential annual losses estimated to be in the hundreds of millions of dollars. When the lanternfly feeds, it excretes honeydew, a sugary substance that promotes the growth of black sooty mold. This mold covers the plants, impairing photosynthesis and weakening the trees, which compounds the ecological and economic harm linked to the Tree of Heaven.
Health Hazards and Nuisance Factors
The Tree of Heaven is also a direct source of discomfort and health issues for people who live near it. The male flowers, which appear in late spring, produce a strong, offensive odor that many people find unpleasant. This smell is often described as rancid, similar to burnt peanut butter or stale athletic socks.
Contact with the plant’s sap can lead to skin irritation or dermatitis in sensitive individuals. The sap, found in the leaves, bark, and seeds, can cause a rash or other adverse skin reactions upon exposure. Although rare, more severe reactions, such as inflammation of the heart muscle, have been reported when the sap enters the bloodstream through broken skin.
The tree also produces pollen, which can contribute to seasonal allergies. In addition to the smell and potential for skin irritation, the tree’s tendency to drop its large leaves and numerous winged seeds creates a constant nuisance for homeowners. This combination of foul odor, minor health risks, and mess makes the tree a significant detractor from the quality of life in urban environments.