What's the big deal?
Except for a few nunatuks, most of Alberta was bare gravel or sediment sometime in the last 10,000 years. Had it not been for alien invasions, there would be no plants here at all! Homo sapiens has long been part of the evolving ecosystem here, so that's nothing new either. However, over the last 300 years or so the rate at which new taxa have been introduced has increased dramatically, as has the human population and it's modifications of the environment. Perhaps this is a matter of taste and nothing more, but we'd like to see things slow down again and hope that you agree.
If disturbances or climatic extremes recur that have been absent for the last 100-300 years, the day may come when many aliens cannot survive here. Native ecosystems have survived the worst the last 10,000 years or so had to offer. Recently introduced alien invaders may be doing fine for now, but may not be so resilient when faced with extreme conditions. We hope this won't happen after it's too late for the native plant communities that evolved under the old regime to recover from the impacts of alien competition. That said, it's also possible that our climate may be changing as rapidly as our flora.
Aliens are not the only vegetative threat to native ecosystems. Prior to settlement, some native plants were constrained by the former regime of periodic disturbance, now altered by changes in patterns of human use and preference (fire suppression instead of setting fires deliberately, for instance, extensive mechanical soil disturbance, or year-round grazing by cattle instead of seasonal grazing by migrating bison). Now that their former constraints have been removed, some native species challenge the preservation of natural areas because former equilibria, maintained by the pre-settlement disturbance regime, have been upset. However, they are not aliens, and in most cases are not listed here.