Hello Wayne, What ecosystems have you witnessed "colonization" ecology in? Invasive plant ecology is different in different ecosystems, though disturbed landscapes, landscapes highly managed by humans, or those close to human development generally tend to be popular with most invasive species in most regions. Also it depends on how well established the invasive plants are. I'll bet promoting a healthy, native ecosystem and preventing further disturbance may prevent exotic species from establishing in a particular area. However, if they are already well established and mature, or have completely taken over, you may need to employ some eradication (I prefer "management", as it is virtually impossible to eradicate some species) methods. Also, what do you mean, by "used?" Did you plant them, or harvest them for a particular use?
~Chris
