TREE OF HEAVEN: FRIEND, FOE, OR FRENEMY?
There are trees busting through the nature-squelching asphalt of my neighbor's courtyard. When I walk to work, I see one growing right out of a sewer grate where one week prior there wasn’t even the faintest sign of life. They're everywhere in NYC, and seem to come from nowhere. They're all the same type of impossibly tough tree: the Tree of Heaven, a.k.a. ghetto palm, or as botany nerds would tell us, Ailanthus altissima.
Some see the Ailanthus as a weed, the veritable cockroach of trees. To be destroyed and driven out. But I see it more like a New Yorker. Persistent, resilient, able to survive and even thrive in the most unlikely cracks and gutters of the city, often seemingly on nothing.
Their opportunistic hardiness means they grow where other trees can't, or wouldn’t dare try. E.g., there are five ghetto palms sprouting directly from my apartment building roof. My landlord keeps trying to eliminate them but the sprout back. Two are growing right from brick wall, and the other three miraculously burst forth from the silver tarpaper. No, I'm not advocating leaving trees to grow right in your home's infrastructure but it does inspire awe.
When a huge back extension was added on building next door, suddenly there were balconies ablaze with “security” night lights and allowing nosey neighbors to see right into my kitchen window. I used to have an unobstructed view of oaks and Trees of Heaven all the way to the end of the block. I was grudgingly mulling over window treatments and fantasizing about taking a BB gun to the new glaring utility lights. I could hear the satisfying high-pitched popping explosion in my mind’s ear. But before I got any closer to realizing my vandalistic fantasy, something amazing started to happen.
First, like grasping fingers, the very tips of three dark green pointy leaves attained the bottom of my second floor window. Within two weeks, three fine, chartreuse branches reached across the bottom of the window. Two months later, like a divine intervention, this new Tree of Heaven grew into a living screen, offering up a thick spray of leaves to shield me from the visual noise of the offending new construction..
This magic beanstalk-like tree deeply piqued my curiosity. Some say the beginning of wisdom is calling a thing by its right name. While a little research taught me what it was called, I otherwise knew nothing about Ailanthus altissima. I was impressed by its protective heroics (at least in my personal situation) and its Houdini-esque ability to emerge alive from the most improbable places.
I began to suspect there was a dark side to this Tree of Heaven. That it might be…an invasive species. One that is introduced from another ecosystem and threatens the environmental balance of its new home. In fact, my detective work soon lead me to discover the Brooklyn Botanic Garden Gardener’s Desk Reference includes the Ailanthus altissima in the top 10 list of “worst invasive species”!
The main problem is three-fold: the Ailanthus creates an unusually large number of seeds with excellent self-sowing success; it produces a toxic substance that inhibits the growth of most native species; and it grows extremely rapidly – easily 6 feet per year – thus intercepting sunlight while slower sapling species below die off in the shadows.
But in my view, the Tree of Heaven should be judged in context. When it springs to life in an otherwise dead asphaltscape, it brings the benefits of oxygen creation, carbon dioxide and sulfur dioxide absorption, shade to help cool buildings, and habitat for birds and squirrels. Not to mention the aesthetic pleasures of leaves rustling in wind or tinking with rain, or the poetry of shifting shadows, cast by moonlight-silvered branches.
Like the Chinese gold rush immigrants who brought it to North America, the Tree of Heaven is largely underappreciated. You could say it is a victim of its own success. The parks department won’t even allow the Tree of Heaven on its property. Gardening guides instruct to avoid it like the plague. But I maintain that there is a place – are many places, actually – for the Tree of Heaven in our urban ecosystem. It can be an excellent scrim between neighboring buildings, and brings all the positive effects of having a little piece of nature outside your window. So why not let the ghetto palm live where other trees can’t?