There’s a tree that’s widespread in my NE Portland neighborhood.
No one plants them. Because of high rates of seed production and germination, they grow as volunteers. You might not notice the young tree hiding at the base of a fence post.
It might show up as a welcome bit of green in a neglected spot. It’s not bothering anyone in a weedy curbside strip.
Or distracted by garden flowers, you might not notice it’s there.
Tree of heaven, Ailanthus altissima, is not a tree most people want to host on their property. It’s considered highly invasive. It’s quick to establish on disturbed sites and is thicket forming. Left alone, before long a yard might host 80-foot specimens to the exclusion of any other tree.
Once it gets too big to pull out completely by hand digging, it’s very challenging to remove this tree. Cutting stimulates more vigorous growth, it resprouts from stump and roots tenfold, and in most cases it can’t be killed without chemicals. Here’s a tree around the corner on my block someone has attempted to thwart by girdling.
How much is this tree suffering? Not very much.
It doesn’t happen overnight, but let go for too long and eventually you’ll see a rearrangement of any concrete structures in the rootzone of this tree.
Not to turn this into a horror show, but I couldn’t resist showing a healthy little sprout from a mass of stumps that otherwise gives the appearance of having been put to rest long ago. The base is over 5 feet long.
The time to get rid of this is now, when it looks like this:
Ailanthus altissima can be mistaken for other trees with pinnately compound leaves. Distinguishing features include leaf arrangement, number and shape of leaflets, flowers and seeds. OSU Department of Horticulture lists some useful facts here.
Other resources can show and inform better than I can. Incomplete at best, here’s just a few tips. Walnut leaves are similar, but English walnut leaflets are larger, rounder, and black walnut leaves are toothed on the margins. For walnut, look for the large green fruits, or furrowed bark pictured below. Tree of heaven bears seeds in a samara like maples, and has smooth bark. Walnut can appear similar as a young tree and like ailanthus they also get tall, shading out other plants, and produce toxins to inhibit growth of other near by plants. (Yes, you might want to yank those seedlings too.)
Finely toothed margins on sumac leaflets, below, distinguish it from the tree of heaven.
On the reverse side of the leaflets, look for a small circular gland at the tip of the lower lobes for positive identification of Ailanthus altissima.
Here is tree of heaven in flower:
As humans, it’s inevitable at times that we assign judgement to plants based on their aesthetic value for garden use or ecological function in natural areas. Even though images like the one below keep me awake at night, I have a little trouble with this because of course trees themselves are without intent, positive or negative.
I look over my back fence at a quickly maturing specimen and wonder how large it will get. My hope is that it will be removed some day soon, halting damage to the home’s foundation and preventing seed dispersal to my yard and many others. But I’m skeptical — each tree of heaven in my neighborhood is a short stone’s throw from the next.
For further reading, here’s a perspective and lots more information I encountered on a blog called Necessary Forests. The City of Portland Bureau of Environmental Services also has this bulletin on Ailanthus altissima.