Natives, Nonnatives, and Invasives!

This morning, which marked our second week and fifth day of class, we spent a few hours with Tom Lee investigating nonnative and invasive species in College Woods.  We learned that the real concern with invasive species are those that invade and then change the natural community.  I was surprised to find that of the over 2,500 species of vascular vegetation found within New Hampshire, about 500 of these are classified as nonnative species, and of those 500 species, only about 50 are classified as invasive species. 

Our main question of the morning was: Why are invasive plants so successful here?
 As we examined the reasons for why we would find, for example, glossy buckthorn on one side of a path but not the other, we found that a whole host of factors - soil composition, light availability, seed dispersal, and many others, can be the deciding factor in where a nonnative plant takes root.  We also discussed a few hypotheses that explain why a nonnative plant would be more successful here in the new world, than they were/are in the old world: the two main hypotheses being the enemy-release hypothesis and the disturbance hypothesis.  I learned that the enemy-release hypothesis "which states that plant species, on introduction to an exotic region, experience a decrease in regulation by herbivores and other natural enemies, resulting in a rapid increase in distribution and abundance" - http://www.sciencedirect.com/science/article/pii/S0169534702024990.  In this way, invasives are twice as likely to get a disease at home - in their native ecosystem - than in a new ecosystem.  The disturbance hypothesis explains the vigor of nonnative, invasive species as the result of our own human messes - whenever we create a disturbance in an area, we have opened it up for nonnative species to take hold and basically take over if they have the capability. 
Whatever the reason, the underlying problem with invasive species is how they change, and really mess up the progression of natural succession in the area.  And for many, the financial cost to get rid of invasive species is too great to bear any really onslaught against these species.  So what will New England forests look like in the future if we are unable to find a cost-effective way to uproot these invasives? Will future generations eventually call some of these invasive species native?