Ailanthus Rising

Tree of Heaven. Ghetto Palm. Ailanthus altissima. Where this particular story begins is with my son, who was writing up a project for his urban geography class in which he examined our nearby Macauley Park, a small triangular sliver of green formed where Kingsway, the diagonal thoroughfare through East Vancouver, intersects with the regular cartesian street grid. McCauley Park features a bus stop, some picnic tables, a statue commemorating Vietnamese immigrants to Vancouver, a collection of lovely magnolia trees, and one giant tree that towers over everything else—a tree no one knows, other than “that big tree in the park.” It was March when my son researched his project, and there were no leaves yet, so it wasn’t easy to identify the tree. And notably, this huge specimen is strangely absent from Vancouver’s Street Tree open data portal, maybe because the tree pre-dates the data.

It is a big tree, almost 2m in diameter and at least 20m tall; it dominates the park. But when you stand under it, all you can really see—apart from its elephantine trunk—are the magnolias that grow in the tree’s understory. From a distance, it’s just that big tree in the park.

Once the leaves came out this spring, I made a bit of a spectacle of myself wandering around with my neck craned, trying to see the leaves. They’re pretty distinctive, actually, and armed with my small collection of tree guides, I had no trouble with the identification: Ailanthus altissima or Tree of Heaven, a native species of China. Now, I just had enough of a recollection to go looking, and sure enough, this is the tree mentioned in the Chuang Tzu (or Zhuangzi) story about the tree that is so gnarled as to be judged utterly useless—but its uselessness is the very thing that leads to its great age, and size.

Just a couple of seconds of Googling gave me the other popular story about this tree: it is the infamous “Ghetto Palm” that has taken over neighbourhoods in Detroit, Baltimore, New York, and other big American cities (“A Tree Grows in Brooklyn,” right?), bursting right through the pavement, straight out of the foundations of buildings. This thing will grow anywhere, and in the summer it produces zillions of samaras (that is, seeds with wings, the kind that fly on the wind). So Ailanthus is considered wildly invasive in most places.

I checked our local bible of urban trees, Gerald Straley’s Trees of Vancouver (UBC Press 1992), which does cite our “most massive and attractive specimen” in Macauley Park, but offers the following comment:

This native of China is among the most tolerant of all trees to city conditions. It is often seen in eastern North American cities, where it is considered a weed tree because it reseeds freely and it has become widely naturalized. In Vancouver it does not usually reseed, is not weedy, and becomes an attractive specimen tree, if given time.

Hmph. Maybe things have changed since 1992; or maybe Straley merely drove by in a car and didn’t stop to wander the streets here. Because if you take the time to stroll down East 15th Ave directly opposite Macauley Park, you’ll see the offspring of this massive and attractive speciment growing out of the sidewalk, out of the pavement, out of the foundations of buildings, just like it does in Detroit.

I started walking the streets and especially the back alleys in the blocks around this big old tree. The offspring of this thing are everywhere, and anywhere they have been allowed to grow up, they are now mature enough to be producing seeds of their own and throwing them to the wind. Mature trees can be found in alleys about a block or so away from the park, and small seedlings up to three blocks away from the original tree. It’s become a bit of a hobby for me when out walking the dog to look for baby Ailanthus growing in the cracks in the pavement around the neighbourhood.

It would be easy enough to be upset about this spreading weed, with its dodgy (and frankly racist) reputation. But it’s also not hard to see this as one of those inspiring stories where, even in the teeth of environmental disaster and collapse, we see mother nature coming back with a vengeance. Ailanthus will grow bloody anywhere. It doesn’t apparently need much in the way of water or soil. Vancouver’s three straight years of summer droughts don’t seem to have done anything to discourage Ailanthus. And its prolific explosion of winged seeds is nothing but astonishing; Macauley Park the other week was covered in a carpet of reddish samaras—while city workers with shovels and hoes dug the seedlings out of the flowerbeds.

Otherwise it grows wherever it is allowed to, or wherever it escapes notice. It becomes part of the invasive wildlife of Vancouver, along with the blackberry canes, Japanese knotweed, English ivy that flourish in the alleys, vacant lots, and laissez-faire backyards. Ailanthus isn’t really a local threat; if you find one you don’t want, you just cut it down or dig it up; it’s not an unstoppable green juggernaut like knotweed. Then again, if you read the Wikipedia page on Ailanthus, there are plenty of stories there of it taking over swathes of landscape from native plants (and that story never gets old).