This small tree is growing in numerous places on my property, around the edges of woodland and amongst bushy undergrowth. The bark is smooth and cherry-like on the branches, but rough and flaky on the trunk. It doesn't match any cherries in my Trees of Ontario reference book. Is it Buckthorn?

Yes. You may want to try to kill it if you can. It's an invasive species and often referred to a "green death" by ecologists who manage native woodlands.

Thanks for the positive ID, Kent. I'll add my pic to the ATP plant database. I think buckthorn falls short of being invasive in this climate zone. It is short-lived and is out-competed by wild apple, dogwoods, cedar, maple, and ash. I won't encourage it to grow in the cultivated part of my property, though.

It's unlikely to be a problem in the cultivated part of your property, that's true, but the woods are probably a different story. Land managers throughout the upper Midwest and Northeast U.S. consider it to be one of the biggest threats to their forests.

The fact that you stated it is growing in numerous places on your property and you did not plant it would definitely indicate that it can be and probably is invasive. We need to see beyond our own property and watch out for all the land. Thank you for listening.

Point taken!