>  few trees can survive a large hollow for long

Again, speaking from personal experience of owning a deciduous hardwood wood lot for 25 years, trees can live for many decades completely hollowed out. We have several magnolias that are immense, being probably 100 years old (judging from aerial photographs). They frequently grow in pairs so when they mature they are leaning away from each other at the crown. In fact, it is beyond my comprehension why the hollowed leaning trunks don't fall down. Evidently a hollow hard trunk can maintain long past the point I would have guessed it would flow over. Willows, on the other hand, blow down all over the place. I am attaching a picture of one of the smaller pairs. The big one is so big that it's hard to get a decent picture of it, to give a sense of what a towering beast it is. 

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