My speculation is that just as critters above the ground go after stressed foliage, critters underground go for stressed roots. I've had two cases where gophers gnawed essentially all the roots away. One was Katharina Ziemet on it own roots - a multiflora hybrid. The other was Cary Grant on (presumably) Dr Huey rootstock. I believe that KZ was not getting enough water; CG was not getting enough sunlight. KZ is well branched and full of leaves, so it probably has higher water requirement for its size than most of my roses; and it was in a spot with punishing levels of sunlight. CG was in the shade of Graham Thomas so it was also being crowded a bit.
I suspect that Crepe Rose, on its own roots, got materially nibbled last summer. I pruned it severely as it wilted; but since it's not in commerce right now, I did not have the heart to dig it up. I'm overwatering it a bit this spring, hoping that what roots the gophers left intact will be enough to support the several green canes remaining. It's not clear how this rose was stressed when nibbled: crowding or drought. It's probably planted too near La Ville Bruxelles, which was in place four years before Crepe Rose was planted .
The stress theory could explain why new roses get hit before established ones. Of course, when a rose has lots of long filamentatious roots rather than a few fat roots, the roots are much more difficult for critters like gophers to consume. When gophers are to blame for rose failures, this makes multiflora rootstock better. Finally, gophers are creatures of convenience as we are. So some of it depends purely on the proximity of a rose to a gopher tunnel.
I also lost an aspen and half an apricot tree to gophers during the two years in which I took a hiatus from trapping. I hate to do it, but the traps are back. And roses are feeding on my gophers, too.
