Dear salmo,
Just a guess but look at how browns have out competed brook trout in PA for a clue.
Browns are invasive in Colorado too, though I know few CO fisherman who care. Rainbows are a west slope fish, supposed to be only in streams on the western side of the Continental Divide. Cutthroats are native CO trout throughout the State.
With invaders everywhere, can you see how and where brook trout can carve out a niche?
I'm not trying to be a jerk when I say that. We've moved a lot of fish around in this country and there are bound to be both winners and losers.
Regards,
Tim Murphy 🙂