Species Profile: Tree of Heaven

In the novel “A Tree Grows in Brooklyn,” the tree-of-heaven is described as follows: “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… survives without sun, water, and seemingly earth.”  Indeed it is one of the most stress tolerant (high pH, drought, salinity, air pollution, compact soil) and fast growing trees (more than one meter per year as a sapling!) found in North America, making it a formidable invader and a problem in forested and urban environments.

Tree of heaven (Ailanthus altissima), introduced from China in the 1700s, is short-lived (50 years) and usually gap-obligate (needing full sunlight).  It has invaded much of the USA from Iowa to Texas to Massachusetts and also along the West Coast (as well as throughout Europe, and southeast Australia), most commonly along roads, fence lines, and railroads, and at abandoned mines or dump sites.  Ailanthus can quickly colonize areas of natural forest that have been disturbed by fire, cutting, or heavy insect damage.  The tree outcompetes native forest hardwoods due to its fast growth, many seeds (hundreds of thousands!), and suppression of other species by releasing toxins from leaves and roots (called allelopathy, in which plants release chemicals to kill other plant species).  Ailanthus can grow in concrete and causes urban problems including damage to building foundations and sewer pipes (not to mention the awful smell of the male flowers).

Tree of heaven branch
Tree of heaven branch, from invasive.org

Ailanthus can often be identified simply by its extremely fat twigs with large buds, astonishing growth, and long (more than 12”) compound leaves with 11 to 25 leaflets.  However, its bark and leaflets may be confused with ash, black walnut, and other native species.  Ash has opposite rather than alternate leaflets and walnut species have fewer and fatter leaflets.  More good photos and descriptions can be found here and here.  An excellent general guide to native species and their invasive look-alikes is here.

The tree is incredibly difficult to eliminate once established.  If cut, the tree vigorously sprouts from the stump or roots, and combinations of mechanical, chemical, biological and thermal treatment may be needed (application is described here).  Young trees can be removed by hand pulling but you must be sure to remove all root fragments, which can sprout new trees, so pulling in wet soil is helpful.

As it has reached a high volume in some states, and requires high investment to eradicate, ailanthus is a good example of an invasive species that, while it cannot be eaten (sorry, no recipes!), has other uses and can be marketed, providing an economic incentive for land owners to manage this invasive.  In addition to larger scale uses such as pulpwood, the wood can be used as firewood- it is relatively hard and heavy, comparable to oak, ask, maple and hickory.  It must first be dried well for one to three months (preferably away from your home as it harbors carpenter ants!).  A very practical and interesting summary of other uses, and programs by the Department of Forestry in Virginia to test the properties of ailanthus wood, can be found here, and more recommendations are found here.  As these publications show, it can also be used to make charcoal for cooking some of the other tasty invasives found at Invasivore!

Here are some photos of ailanthus outside my work, in Italy.  It commonly colonizes the edges of walls and parking lots.  You can click for zoom ins.

You can see here the bright colored seeds this time of year.
Ailanthus
Ailanthus tree 

This tiny seedling is growing right out of the wall. Not a bit of soil!

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