Far as I know there are very few true "barren" landscapes where anyone actually lives or would ever bother moving to. Desserts are not lifeless, for example. Yes not as diverse as rainforests, but not lifeless and a surprising amount happens in them. Furthermore affecting one ecosystem affects the next. They do not operate in isolation. Just take the example of beaches, build sea defences to protect your down and further down the coast another area, previously never affected by erosion, suddenly gets eaten away by the sea. As for control - bleh. You'll always have escapees of some kind; and if the hybrid is designed to resist natural predators and be big, healthy and produces lots of seeds - well then you don't need many escapees to cause a major problem.