My mistake was not noticing the young tree when it first sprouted behind the garbage cans. In a couple months it’s grown into a robust young thing, insinuated in the slit between the asphalt of the alley and the foundation of my house. Now, with branches higher than my thighs and roots entwined with the house foundation, the sapling refuses to be yanked. When I tug hard, the upper branches tear away, leaving the stalk and the roots behind. I hold the leaves in my fists and disgustedly contemplate herbicide.
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To call the species fast growing is as much an understatement as saying that light travels at a pretty good clip. Scientists have monitored specimens that have sprouted 12 feet in a single season. This can be a good trait if you’re impatient, but it also makes the ailanthus a poor choice as a street tree. Speedy growers tend to be weaker than species like oaks, which grow ponderously, inch by inch, year to year. The fragility becomes a drawback when high winds break off heavy branches and drop them onto the hood of a car or the cranium of a pedestrian.
Frederick Law Olmsted created an ailanthus grove in Central Park in the late 1850s, and for a while trees of heaven were planted enthusiastically in eastern cities. But this love affair with the weirdly tropical-looking plant faded fast when its astonishing skills in procreation started making it an urban menace. The trees began to crop up everywhere and killing them off was no easy task. Female trees send out a million seeds each summer. And they don’t take chances with only one method of reproduction; each tree also has the capacity to send out suckers from its roots that saturate the surrounding area with new clones. Cutting one down may result in the creation of fifteen more. By 1875 the District of Columbia was fining citizens who allowed trees of heaven to grow, and other cities halted their once-enthusiastic planting.
When the tree of heaven first gained its powerful foothold in northeastern cities, biologists feared it would take over in the native forests as well. There seemed to be nothing to stop it. Except, as it turned out, the woods themselves. Exposed to the fertile conditions of a forest, ailanthus loses its competitive edge. Other trees–the oaks, maples, and ashes of the world–are so successful in this environment there’s no room for trees of heaven. Studies have shown that when ailanthus seeds are placed in rich soil and in sidewalk cracks, the trees sprouting from cracks have a higher survival rate. In one case, a forester from Milwaukee grew ailanthus trees in a nursery and found that most died over the winter. He surmised they grew so lushly that they didn’t properly harden off in preparation for winter.
