What makes you say that? It doesn't take too much knowledge to maintain a biosphere, otherwise it would have collapsed long before humans arrived on Earth. It seems more to do with how cautious you want to be, how far a race is willing to push the environment in return for faster progress.

I also suspect that any extraterrestrial intelligence capable of making a signal detectable by our equipment would have given up its biological roots a long time ago, as life as we know it is badly adapted for space travel.