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.

> It doesn't take too much knowledge to maintain a biosphere, otherwise it would have collapsed long before humans arrived on Earth.

Well. It did. Multiple times.http://en.wikipedia.org/wiki/Extinction_event

It's just that things tend do kick back in if you give them few millions of years.

> However, it's likely that any extraterrestrial intelligence capable of maintaining life on it's home planet, will have an understanding of their fellow life forms, which is more than we have.

That's quite the assumption. Right now, our sample size of one shows the opposite.