What is the Tree of Heaven?
The Tree of Heaven or Ailanthus altissima is a plant native to areas of Korea, Taiwan, and China.
Oddly enough, much like Spotted Lanternflies, Tree of Heaven was first brought to North America via the Philadelphia, Pennsylvania area in the late 18th century. The tree can tolerate low pH, high salt, poor quality soil, and heavy drought conditions which made it popular for planting as it would take hold and grow in many applications. It later fell out of popularity as those investing time in the plants realized the true nature of the tree.
The Tree of Heaven grows extremely quickly. It is one of the fast growing trees now found in North America. In fact, the trees grow faster in North America than they do in their native Asia. The tree can take advantage of almost any soil type and is sometimes found where no other plant or tree would prefer to grow. They do require full sun to grow, and are severely stunted in dense shade. Interestingly, where there are large areas of Tree of Heaven growth, there are usually not many other plants or other trees growing in the immediate area, even in good soil/sun conditions. This is due to a toxin that the tree produces to prevent any competition from neighboring plants. Specifically, the Tree of Heaven produces Ailanthone, which is considered an allelopathic chemical which is simply a chemical produced by a plant that has an affect on another plant, either positive or negative. In this case Ailanthone is thus allelopathically negative (or herbicidal) to the plants around it. The Tree of Heaven is also known to have a distinct unpleasant odor emanating from the stems and leaves of the tree.
Why is Tree-of-Heaven considered invasive?
The inhibition of neighboring plants and extremely quick growth is why the Tree of Heaven is widely regarded as invasive outside of its normal areas.
The Tree of Heaven has many factors that make it incredibly invasive and hard to control.
- The tree creates an overabundance of seeds which can be propagated and grown into new trees. Some trees may produce several hundreds of thousands of seeds in a season. The seeds are usually singular and not connected to other seeds, leaving them very light and able to travel far distances on wind and water.
- The seeds can survive poor soil conditions, low soil conditions (like in between cement cracks, on the side of the road, etc.), they are also heat tolerant, drought tolerant, salt tolerant, wind tolerant, and pollution tolerant.
- As mentioned before, the tree grows extremely quickly both branches and stems. The tree can create quite an extensive root network rather fast.
- The tree can reproduce both sexually and asexually. Asexually, or vegetatively, the tree can create numerous sprouts. In fact, Tree of Heaven is known to be a competent stump sprouter. This is why it's not enough to simply cut the tree down to a stump. The stump and its roots must be removed to fully destroy the trees growth. The Tree of Heaven aggressively grows back after being cut or broken.
- Many potential predators to a growing Tree of Heaven may avoid the tree entirely due to the unpalatability of the leaves, possible due to the toxic allelopathic nature of the tree.
What does the Tree-of-Heaven Have To Do With Spotted Lanternflies?
While earlier SLF nymph instars (instars are the stages of development an SLF experiences) may colonize and feed off of many varieties of plants, later stage nymph instars and adult Lanternflies preferentially both feed off of and lay their eggs on the Tree of Heaven. One reason may be due to its familiarity with the plant, considering they are both native to China and other areas of Asia.
An additional reason postulates that Spotted Lanternflies prefer to feed and lay eggs on trees with toxic metabolites. As previously mentioned, the Tree of Heaven contains ailanthone which is cytotoxic to some plants and potentially some animals. This allows the Spotted Lanternflies to feast and lay eggs in an environment that will be mostly left alone by other predators. Lanternflies may also sequester and take in some of the toxins making them unpalatable, which may work to prevent other species from eating them. However, Spotted Lanternflies will colonize and feast/lay eggs on many other plants and trees in the absence of Tree of Heaven It is noted that Spotted Lanternflies have an affinity for higher sugar plants, hence why they are a threat to many agricultural industries, especially those involving grapes and grape vines.
Tree of Heaven Removal
Removal of the Tree of Heaven is an important but potentially
tedious task. As mentioned previously, it’s not enough to simply cut the tree
down to the stump, as the Tree of Heaven is a vigorous stump sprouter and will
come back with a vengeance. Most effective removal applications involve the use
of a systemic herbicide. Systemic refers to the “translocation” of the
herbicide throughout the entirety of the tree which allows it to seep into the
circulation of the tree system and destroy more of the tree than if it were a
simple “local” herbicide. There are a
few methods of removal, and their use generally depends on the maturity of the
tree itself. Smaller trees and Larger trees may benefit from different
techniques.
The most commonly used systemic herbicides include
Glyphosate (commonly found in Roundup) and Triclopyr (commonly found in Weed-B-Gon,
Brush-B-Gon, and Turflon). Herbicides should be applied from roughly July to
mid-October. During this time, the
carbohydrates created during photosynthesis are being transported throughout
the tree, including the roots. Applying herbicide during this time allows the
chemicals to “hitch a ride” and spread throughout the tree.
For nascent seedlings, it is possible for one to manually
mechanically pull the tree out of the ground. Care must be taken to ensure the
ENTIRE tree is removed, including all of the roots. Certain soil conditions, such
as moist/damp soil will allow for easier removal of the tree. Failure to remove
the entirety of the tree would most likely result in the tree resprouting and
continue to grow.
- Foliar Herbicidal method – The foliar herbicidal method is used on smaller trees (typically under 10 feet), especially those growing densely packed together. This method allows most of the tree to get treated by the herbicide, including the stem, leaves, and other above ground portions of the tree.
- Basal Bark Method – This method would typically require a backpack sprayer. Herbicide is applied to the bark near the base of the tree, hence “basal”. Typically, the bottom foot or foot and a half of the tree is wetted with herbicide. This method requires an oil-based solution herbicide such as triclopyr ester. The oil allows it to stay on the bark and seep into the tree. This method typically would not be used on trees that have a trunk diameter of more than 6 inches. This method would need to be used by someone licensed to use triclopyr ester.
- Hack and Squirt – Sure it sounds funny, but it’s a common method for fully grown trees that are more than 6 inches in diameter. This method CAN be used on smaller trees if warranted. The method involves using a hatchet to impart cuts into the trunk (stem) of the tree. Typically, 1 cut per inch of diameter is warranted. After the cuts are made, concentrated herbicide, especially Glyphosate is sprayed into the wounds. Spacing between the cuts is important, as you want the tree to maintain its ability to “translocate” nutrients throughout the tree. Inhibiting the trees ability to do this will not allow the herbicide to spread throughout the tree.