Tree of Heaven trunks marked for removal from a natural maple forest.
Tree of Heaven trunks marked for removal from a natural maple forest.

(Click on any photo to enlarge)

   An invasive species is a non-native animal or plant (tree, in our case) that negatively affects the economy, ecology or environment around it. Invasive species may be introduced to our region accidentally, such as a seed hitchhiking on a cargo ship, or intentionally, such as by sale through a nursery. keith_3-logo

   Some non-native trees are not considered invasive, such as the Norway maple. Although Norway maple is not native to North America, it does not negatively affect its surroundings. Trees are usually considered invasive if they reproduce prolifically and displace native vegetation.

   Tree of Heaven (Ailanthus altissima) is native to China, Taiwan and Korea and was first brought to the United States in 1784 at a time when Chinese art had a heavy influence on Western culture. It was planted extensively as a street tree in the 19th and early 20th centuries due to its high tolerance of the poor growing conditions found in the urban environment, as described by Betty Smith in “A Tree Grows in Brooklyn”:   

   Tree of Heaven is a large tree, reaching up to 80 feet tall and 3 feet in diameter. It regenerates through suckers shot up from its root system up to 30 feet away from the trunk, and creates enormous amounts of winged seeds disseminated by wind. This style of seed is called a “samara,” the same kind present on maple trees. Unlike maple trees, however, Tree of Heaven is highly tolerant of dry, nutrient-poor soil and is notorious for its ability to grow almost anywhere. Tree of Heaven is also known as Chinese sumac because its leaves closely resemble those of our native sumac. “Stink tree” is another common name resulting from the repugnant odor the tree produces.

Whether young or old, Tree of Heaven has very smooth, light gray bark.

Whether young or old, Tree of Heaven has very smooth, light gray bark.

   “There’s a tree that grows in Brooklyn. Some people call it the Tree of Heaven. No matter where its seed falls, it makes a tree which struggles to reach the sky. It grows in boarded up lots and out of neglected rubbish heaps. It grows up out of cellar gratings. It is the only tree that grows out of cement. It grows lushly … survives without sun, water, and seemingly earth. It would be considered beautiful except that there are too many of it.”

Tree of Heaven's leaves resemble those of our native Staghorn sumac.

Tree of Heaven's leaves resemble those of our native Staghorn sumac.

   Tree of Heaven is an opportunistic species and tolerates pollution extremely well, though it rarely lives more than 50 years. It is often found on mine reclamation sites where no other trees can grow due to the presence of toxins such as sulfur dioxide and mercury. Its root system is very well adapted to dry conditions, seeking moisture from sewer pipes in urban areas and storing water for extended periods. The root system produces a unique chemical called ailanthone which strongly inhibits the growth of other plants, though not of itself. This chemical weaponry, in combination with its aggressive approach to reproduction, is what gives Tree of Heaven the ability to obliterate natural forests.

   Tree of Heaven poses a real threat to natural forests in our region and is currently found in all 92 counties of Indiana. It is not uncommon to find entire hillsides in southern Indiana covered with nothing but Tree of Heaven, the native tree species long out-competed. Considered a noxious weed, it is quickly becoming more common in northwest Indiana as our natural areas are disturbed for new development.

   Tree of Heaven should not be planted under any circumstance and should be removed and treated with chemicals to prevent aggressive re-sprouting at the stump where discovered.

KEITH O’HERRIN is the City Forester for the City of LaPorte. He can be found at the Park and Recreation Office at 250 Pine Lake Ave. or reached at 326-9600.

Tree of Heaven will grow almost anywhere.

Tree of Heaven will grow almost anywhere.