Tag Archives: ecology

❤️ Weed Trees ❤️

Here’s a dictionary definition of a weed: “a wild plant growing where it is not wanted and in competition with cultivated plants.”

That definition leaves out a lot, doesn’t it? You hear the word “weed,” and somewhere in your mind you’re probably thinking “annoying” and “unsightly.”

People talk about “weed trees,” too. They spring up on their own, often in places where other trees may struggle to thrive or even survive. They’re exceedingly common. They may have characteristics that don’t fit the classic image of a tree, e.g., they may be bushy, misshapen, etc. And they’re scrappy: they can out-compete trees that we think of as conventionally beautiful, stately, grand, majestic, noble — all that good stuff.

Boxelder (Acer negundo) comes to mind. It’s a species of maple native to North America. Check out this guy. Talk about scrappy:

Photo credit: Arieh Tal

Here’s its compound leaf with leaflets (7 here but can be as few as 3), to help you identify the tree :

Photo credit: Glen Mittelhauser

Weed tree? Yet entomologist Doug Tallamy says 285 species of Lepidoptera (moths and butterflies) rely upon boxelder to survive their caterpillar stage.

So many bugs! Here’s the secret: boxelder is terrible at doing what many other trees do incredibly well, which is to seal off decay. Which means that boxelder rots. And what loves rotting wood? Bugs!

And birds love bugs, of course. So boxelder indirectly feeds lotsa birds, too.

Can you build a beautiful, long-lasting dining room table out of boxelder wood? Nope. But can you sustain an ecosystem encompassing hundreds or perhaps even thousands of different insect and animal species with boxelder trees? ? Yep.

From Ecology of Center City, Philadelphia by Kenneth D. Frank.

Yes, those are boxelder seedlings, bringing a stone staircase to life. Not bad for a weed.

EWW!

It’s that time of the year.

Chinese chestnut (Castanea mollissima)
Spiky flowers of the Chinese chestnut tree, called catkins.

A large Chinese chestnut tree (Castanea mollissima) is in bloom near my house, and it’s once again filling the air with an . . . ammonia smell which is seriously unpleasant.

The culprits are nitrogen-containing volatile organic compounds (VOCs) which include (for you chemists out there) 1-pyrroline, 1-piperideine, 2-pyrrolidone, and phenethylamine.

Chemical structure of 1-pyrroline

What’s the deal? Presumably the tree evolved this smell to attract pollinators. A recent scientific study of Castanea mollissima in China identified the chestnut’s pollinators as flies.

Those researchers suggest that we should add Chinese chestnut to the list of plants that rely upon sapromyophily for a reproduction strategy.

That is, this tree emits a smell that deceives carrion flies into believing that they’re visiting rotting flesh.

Eww.

Naturally, I cannot help but imagine what it must have been like to be out in the forest when the mighty American chestnut (Castanea dentata), erstwhile queen of the mountainous forests in the eastern U.S., was in bloom.

And, hey, I’d happily cope with a couple of weeks of that yucky odor to have those trees back, safe and sound from the chestnut blight.