According to the USDA Forest Service, an invasive species is defined as “a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” Invasive species along with habitat loss and pollution are the most severe threats to biodiversity and ecosystem function. Why are they such a problem? One factor that my colleague, Lenny Farlee, points to is that people don’t know they have a problem. That is, they are all around us and most folks don’t even know it. People must first be able to recognize invasive species from non-invasive species. One of the more recent invaders is tree-of-heaven (Ailanthus altissima).
Don’t be fooled by the name. They are far from heaven for us. It’s actually been around for a couple hundred years. However, only over the past 10-20 years has it really begun to expand its range. This pattern is very typical of invasive species invasion. Mid-summer is one of the best times to identify and control this tree. Ohio State produced a publication on control methods and this is linked at the end of this article. I want to focus on identification here.
Tree-of-heaven may be confused with similar-sized sumacs or even black walnut to the untrained eye. Because tree-of-heaven can grow very rapidly, they will often have several feet between branching along the main trunk. Some have also described the strong odor from tree-of-heaven similar to rotting peanuts. For most folks, the leaflets and fruit are the easiest features to go by. Each leaflet has one or more glandular lobes or teeth near the base. This is the best feature to differentiate it from similar species of similar size. On older trees, numerous fruit clusters will begin to form towards the end of June and will be present throughout most of July or longer. Black walnuts and other native trees with compound leaves lack these seed clusters.
Figure 1. Tree-of-heaven have pinnately compound leaves with 11 to 27 leaflets. Each leaflet has one to several glandular teeth near the base. These are lacking on other trees and shrubs.
Figure 2. The fruit of tree-of-heaven are winged samaras. They can be green, red or brown in color. Numerous clusters of fruit are easily observed on tree-of-heaven during the summer.
Controlling Non-Native Invasive Plants in Ohio: Ailanthus
Indiana Invasive Species Council
Brian MacGowan, Extension Wildlife Specialist
Department of Forestry and Natural Resources, Purdue University