Behold a dreadful strangling monster!  This entity cannot be easily killed by conventional means and it reproduces both by asexually spawning duplicates of itself (at first attached to the parent by runners) and by releasing tens of thousands of wind-born flying pods.  When these pods land on something they take root and start to grow—even if it is another tree or a roof or a bit of concrete.  This monster comes from the primeval forests of China, indeed it is mentioned in the most ancient Chinese texts, but today it has spread everywhere.  It eats toxins and is not affected by most pollutants or even by high doses of toxic metals. It produces a poison which kills plants. If you live in a major city there is probably more than one outside your door right now!

Ailanthus altissima, the Tree of Heaven (photo by Cheryl Moorehead)

Thanks to the title at the top of the page, perspicacious readers will probably already have guessed that the monster I am writing about is Ailanthus altissima, aka the tree of heaven.  This is one of the most successful invasive species out there.  People unfamiliar with the plant are probably chortling at my rhetoric, whereas people who do know this tree, especially gardeners, are most likely making murderous gestures and exclaiming wild oaths.  The tree reproduces like crazy and it grows with seemingly supernatural speed.  Anyone who has tried to garden anywhere near a tree of heaven has spent a great deal of their time pulling up saplings or sawing them down only to see them rise again and again like the fearsome horde of hellspawn which they are.  When chopped down the tree grows back with redoubled vigor and produces suckers (basal shoots which grow from the roots and produce independent trees).  The tree of heaven may not be a massive clonal colony like Pando, but fighting the suckers and the seedlings and their many offshoots makes it seem like a single malevolent entity. And it is everywhere—when you see a tree growing on top of an abandoned building or sprouting improbably from sheer concrete, it is most likely the tree of heaven.

So Many Seeds!

The tree was not always despised. Eighteenth century European gardeners (under the spell of Chinese gardens and all things Chinese) were beguiled by its swift growth and elegant looks.  They brought the tree to Europe in the 1740s and to the United States in 1784, but, as soon as the tree was planted, the honeymoon ended.  In formal gardens Ailanthus trees tendency to sucker and set seed became very apparent as did the abominable smell of the male trees which produce a urine-like stench to attract unsavory pollinating insects (European botanists should probably have translated the Chinese name before planting: 臭椿 literally means malodorous tree). The tree’s prettiness though undeniable is not as great as that of other Chinese invasive trees like the lovely Empress tree (which is not nearly as aggressive or malodorous).

Samia cynthia--the Ailanthus Moth (note the lack of a mouth--saturniid moths do not feed in their final adult stage)

Aesthetic concerns were not the sole motivating factor which caused European gardeners to import the fearsome tree.  Although the finest silk comes from the silkworm, Bombyx mori, which feeds only on the mulberry tree, a more durable and coarse silk can be produced from the cocoons of the ailanthus moth  (Samia Cynthia) which, of course, eats ailanthus leaves. Ailanthus silk is distinctly inferior to true silk in that it does not readily take dyes, but it is durable and pretty in its own right.  Unfortunately it proved to be too labor-intensive for western production. Ailanthus moths, the huge saturniid moths, which produce these cocoons also went rogue and are now spreading across North America and Europe in tandem with the trees.

The discerning reader may have apprehended that I am no fan of the tree of heaven.  Even literary allusions to the ailanthus are problematic (it is the tree from A Tree Grows in Brooklyn, a novel about alcoholism, poverty, cheating, and misery in early twentieth century immigrant life). However, having said that, Ailanthus altissima demands respect as a supremely effective life form.  It is probably the fastest growing tree in North America and is able to grow 2 meters (6 feet) in a year (as I know from cutting down 15 foot tall suckers in my tiny garden). Additionally the tree produces a chemical, ailanthone, which inhibits or prevents the germination of other seeds and is toxic to other trees.  Ailanthus altissima can live in locations that are dry, salty, or toxic and can survive on water as acidic as tomato juice. For these reasons as well as its staggering number of wind-born twirling seeds it can be found in industrial or urban wastelands where nothing else grows.  It is impossible not to feel a bit of awe for a 50 to 90 foot tall weed.

Ailanthus Trees Growing in a City

Not only is the tree is an opportunist which can live by itself in places too dry or poisonous for other trees but its incredible rate of growth allow it to compete with other deciduous trees by quickly growing into unoccupied canopy space (although adult forest trees in healthy woods can probably out-compete it in the long run).  The tree of heaven pays a price for its quick growth and heavy suckering.  Its life is short and specimens rarely live past 50 years.  However one individual tree is not the problem—if you have one tree you already have many.  Like the Lernaean Hydra, the tree of heaven is a exponentially increasing monster, but something so tough must have a use.  Perhaps a future generation of space colonists living in Konstantin Tsiolkovsky’s fantasy will spend their time wrinkling their noses and wandering why anyone chose to plant such a thing.

A photo from my nearest train station in Ditmas Park, Brooklyn