There are several definitions floating around on what it means for a species to be invasive. A lot of laymen and scientists alike tend to use “invasive” as pertaining to the agressive nature or habit of a species of plant or animal where the new species negatively affects native species, by means of crowding it out; competing for nutrients, food, water, and light; or directly consuming or killing it. That is definitely one way of looking at this phenomenon. I personally don’t subscribe to this narrow viewpoint, because in nature this behavior is a rampant and every-day occurence. Just think of two competing ant hills, or a big pine denying light to saplings of other species or even its own kind. Are there, or were there ever, “safe” and balanced eco-systems? I don’t think so – competitive advantage and opportunistic tendencies are part of the DNA of anything alive today, and even that is sometimes not enough to safekeep a future for the next generation. Today, just like eons ago, the threat could come from a thousand miles away or from the brush or thicket right next to you. Have we, as humans, facilitated invasive behavior? Undoubtedly, our highways and parceling up of ever smaller tracts of land have led to situations where a handful of trees, rather than whole forests are competing with other species under changing environmental circumstances. Now, before I go off on a tangent (and it may already be too late for that) I want to point out that I use “invasive” as meaning “not originating from the eastern US or Canada”, and having arrived here by some kind of human intervention – whether it was last week or 400 years ago. The definition I use does not indicate agressiveness or anything else pejorative. It simply means that a plant or animal is originally native to Europe or Asia. It wasn’t here before, and now it is. Simple. As for the plants thenselves – a good amount of them are quite docile, happy to get along with other vegetation, and more often than not they (as Chris from Forest Keepers pointed out) have nutritional and medicinal value that should make it worth our while to get to know more about them, instead of reaching for the Roundup… I am actually fine with having dandelion and other assorted European and Eurasian species sprouting up. It’s futile to try to get rid of them, at best you’ll get temporary reprieve, and using chemical means just creates havoc downstream and over time in many unintended ways. Maybe the more obnoxious species such as asiatic bittersweet are more deserving of the “invasive” label, but again I am looking at plants from the point of origin, not from any behavioral approach.