Tree of Heaven Damage
Tree of heavens ability to withstand many environmental factors, as well as its ability to spread prolifically through vegetative and sexual reproduction make it extremely invasive.
TOH can interfere ecosystem processes, as it has the ability to out-compete other plants for light, water, and nutrients in sites that have been disturbed. Like many introduced invasives, limited pests and diseases pressure increase its spread potential.
Allelopathy - or the production of toxins that inhibit the growth of nearby plants - is another mechanism in which can help aid successful establishment. The highest concentrations of chemicals are found in young roots, though all parts of the tree (fallen leaf litter, etc) contain toxins1.
Other than being toxic to plants, it may also be toxic to some animals and microbes.
Can pose health risks: pollen grains can be an allergen; sap exposure, in rare cases, may cause dermatitis in susceptible people.
Tree of heaven can cause structural damage to buildings, pavement, and water facilities. Seedlings have been known to establish in cracks in walls and roofs.
Photo by Benton County Noxious Weed Control Board, WA. Available from http://www.bentonweedboard.com/previous-invader-updates-tree-of-heaven