Tuesday, February 22, 2011

Invasive species: Ailanthus altissima (tree of heaven)

A. altissima can grow almost anywhere provided there is sufficient light. This seedling shows less than one season's growth. Note the large, pinnately compound leaves.

Ailanthus altissama pisses me off. This medium sized tree is native to China and is possibly the fastest growing tree in North America. Its common name, tree of heaven, comes from its ability to grow as many as 3 meters towards the heavens in a single growing season. It is a particularly nasty invasive species for a variety of reasons. Like many invasive species, A. altissima reproduces prolifically via both seeds and through its extensive shallow root network. It is also allelopathic, meaning it secretes chemicals that inhibit the growth of other plants. The particular chemical is called ailanthone. It is present in all parts of the plant, including seeds and inhibits cell division in other plants. This can be devistating to the seedlings of native species because they have not had the chance to evolve resistance to A. altissima's chemical attacks.

A. altissama can be found all over Ann Arbor, but it is particularly prevalent in disturbed sites. There are also some cases where it appears as if it has been planted as an ornamental. For example there are several large A. altissima planted in a row between the parking lot on 4th and Catherine and \'aut\ bar. There is also a large female in the parking lot behind Kerrytown.

Form: medium tree
Leaves: large, alternate, pinnately compound leaves, up to 1 m in length. Leaflets are ovate to lanceolate (broader at the base). They taper to the base where they have 4 prominent teeth. On the underside of the teeth there is a single circular scar. The base of the petiole is broad and leaves a distinctive heart-shaped leaf scar on the branch.
Twigs: thick and light weight. Light brown with lenticles.
Bark: thin and graphite to charcoal gray. It is smooth but becomes wrinkly with small tan furrows on older individuals. Some people say it looks like an elephant's skin.
Fruit: Samara (fruit with an airfoil) with seed in center of wing. (As opposed to maples whose fruits are samaras with seeds at the end of the wing.) Prolific seeder, females are easily identified by their large bunches of samaras that persist through winter.
Miscellaneous: A. altissima smells like rotten peanut butter when the bark/twigs are scratched.
Habitat: Light demanding, tolerant of a wide range of environmental conditions (acidic soil, high salt levels in soil, drought, air pollution). Often found in disturbed sites.

Similar species: native shrub Rhus typhina (staghorn sumac) has alternately arranged, long, pinnately compound leaves and could be mistaken for a young A. altissima. R. typhina has much serrated leaflets that lack gland tips. Its twigs are densely pubescent and resemble a stag's antler covered in velvet.

A. altissima regrows and reproduces vigorously. It pays to nip this one in the bud before it becomes hard to manage. Adult trees can be chopped down or girdled. This thought will cause vigorous sprouting from the root system. Fortunately the wood is very week, so you can just mow/kick the sprouts down. If you are willing to use herbicides, an application of oil-soluble triclopyr at the base of the bark in late winter or early spring will do the trick on smaller trees (less than 15 cm in diameter). For larger trees you can strip off bark pieces and apply triclopyr. You can also apply glyphosate on the stump after felling the tree to prevent re-sprouting. As with many invasive species, A. altissima is fire intolerant; regular burning prevents establishment and will any individuals present. Burning is not for novices thought. If you are interested in burning an area to control A. altissima (or other invasives) you should probably cut your teeth by volunteering to help with a controlled burn with NAP or the University. Permits for controled burns are available through the fire department.

Here is something I don't see mentioned often when discussing strategies for removal of invasive species. Almost all invasive plants colonize disturbed areas particularly well. When you remove invasives, you are creating a disturbance, the ideal habitat for a new (or old) invasive to colonize. After removing an A. altissima, you may want to consider planting a native species to replace it so that you are not just creating habitat for more invasive species.

Ann Arbor is fortunate enough to have a city department dedicated to preserving native biodiversity--Natural Areas Preservation. They are a great group of people doing good work and very worthwhile group to volunteer for.

A. altissima is dioecious meaning there are plants with male reproductive structures, and separate plants with female reproductive structures. Here we can see the characteristic samara fruit of a female A. altissima. A mature female can produce literally millions of seeds.

Two A. altissima shoots can be seen on the right side of this picture. Each shoot represents a single season of growth! Note the distinctive, large, heart-shaped leaf scars.

Female A. altissima are easy to identify in the winter because of their persistent clusters of samaras.

If you have any further questions about A. altissima, feel free to leave a comment.

Up next: Rhamnus cathartica (common buckthorn)

Photo credit:
A. altissima seedling: Dalgial
A. altissima samaras: Luis Fernández García
Remaining pictures: Damn Arbor


  1. When do I get my own invasive species post for commonly showing up uninvited and punishing your toilet?

  2. "There is also a large female in the parking lot behind Kerrytown."

    Ben, stop talking about my mom.

    /chris and I trolling your site.

  3. I was wondering if anyone would notice that sentence.