Some of the trees you see in your local forests, local parks -- or perhaps even in your own yard -- may look like they're just innocently standing around, improving our air quality. That's what they want you to think! The reality, however, is that they're on the march, as part of a massive alien invasion. Steve Nix has been scouting these alien invasive trees, and his troubling report does not shy away from alluding to collaborators.

_{Photo of silk tree flower ©2007 David Beaulieu (licensed to About.com)}