Tuesday, April 22, 2008

The sex life of trees

I've been thinking lately about one of North America's least appreciated trees, acer negundo, better known as the box elder or ash leaf maple. This is a tree that is so common, that has been so much of the background for so many places that we've lived up north, that when we moved into our current apartment and discovered one growing on the edge of the patio I didn't recognize it. The last thing I expected to find next to our back door in Atlanta was the same type of tree we had shading our deck in Hancock, Michigan. I actually checked a tree i.d. book out of the agency library in order to pin down the species. I kept thinking, "It looks really familiar. Now what is it?" Definitely a "duh" moment when I learned what I was looking at. (The book did come in handy for identifying the stuff around Atlanta I really had never seen before, like mimosa and balloon nut, so carrying it home from work wasn't a total waste of time.)

Tree i.d. books use terms like "invasive" and "weedy" when describing acer negundo. Maybe "highly adaptable" would be a better term. Box elders like disturbed areas and edge spaces so in urban areas they tend to pop up in vacant lots and along alley fences. Or, in the case of the fellow pictured here (and it is a male tree; box elders are dioecious, which means every tree is either male or female, and those are boy parts dangling there), on the inside of a patio fence. Box elder grows fast so, at least according to the Corin Center for Biodiversity at UW-Green Bay, has occasionally been used in the past as a street tree. Not anymore. Box elders aren't particularly long-lived compared to other shade trees, nor are they particularly strong. They are, in fact, generally viewed with considerable contempt. No commercial value, no long term landscape value, ergo, of no use in general.

The song birds that hang out in the box elder growing on our patio would beg to differ, of course. The mockingbirds, cardinals, robins, and a wide variety of LBBs seem perfectly happy with the tree. And so are we. It may have popped up accidentally not that many years ago (I'm guessing sometime in the 1990s), but previous tenants ignored it. It's now tall enough to provide shade for our west facing wall, which is basically two stories of glass. That tree allows us to keep the blinds open all summer instead of turning our townhouse into a gloomy cave. It's leafy enough to provide shade, but the growth isn't so dense that it completely blocks light -- it just filters it. It may be a fragile tree compared to, for example, a white oak or a sugar maple, but the branches are still more than strong enough to hang a bird feeder or a potted plant from. It doesn't shed tons of crap like the balloon nut tree one patio over from us (although I will concede the balloon nut has showier flowers), and, maybe because it's male and has no seeds it doesn't seem to attract squirrels. I am, in short, rather fond of that tree.


  1. i like the idea of a tree being called ballon nut..

  2. My friend south of Madison, WI is at war with the box elder on his 8 acres. Being a farm boy he gets his exercise (no club for him) by hand cutting down and hauling box elder by the dozens. At the end of January he has a party which features a huge box elder bonfire. Even with his ruthless extermination the box elders still thrive better than his planted hardwoods and conifers. But at least it keeps him in shape.

  3. Box elder is notorious for sprouting vigorously from the stump as well as sending up shoots from the roots. They're not quite in the same class as speckled alder when it comes to being fruitful and multiplying (tag alder has both male and female flowers on the same tree, sends up shoots from roots, and does opportunistic rooting if a branch hits the ground), but box elders come close.


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