Grown by Steve Breyer at Tripple Brook Farm where both species are native. Butternut was already perhaps 15' tall when Steve planted "Concord" grapes beneath. He reports that both seem to be producing well. Nearby are hardy kiwis growing on a much larger butternut, which appear to be smothering it a fair amount. I think what makes butternut-grape work so well is that the grape, in this case, is not vigorous enough to cause much compeition with the butternut. Now it just needs some cool stuff happening in the understory: perhaps something with hog peanut or tick trefoil to fix nitrogen.