They are imported, I don't think they are as bad as what Wood Doctor's post makes them out to be. Although they do pop up readily in disturbed fields. I built a house last summer, and have had quite a few pop up in my new yard (along with a bunch of cottonwoods) this spring and summer. I just mow them over. I am letting one go just for curiosities sake. It has grown to about 3ft over the summer so far. Round-Up will kill them when they are small too. These are the trees that get topped around here and then grow back just as full as they were before you top them although their branches are much weaker than they were before. So it isn't suggested to top them unless there is no other alternative. They aren't the best of trees, but I burn them a lot so I don't think they are as bad as what some people make them out to be. Just my opinion though.
