A similar thing happens with acers. I would be a millionaire if I could have sold all the ornamental acers I have "weeded" out. But we do have indigenous rare ash trees in the Avon Gorge in Bristol, and it is my hope they will spread via their seeds and entice waxwings in good numbers to us. I have just been working among my bluebell plantations which have spread wherever they find a suitable corner and hope they will survive if there is no gardener after me. I agree , James, it is very comforting to realise how powerful nature is and our attempts to tame it( which is what Shakespeare said we gardeners do) are quite puny.