Location, location, location. We have some live oaks here that are just loaded with these ferns. The trees are very old though, perhaps approaching 100 years old! I see no ferns whatsoever on live oaks that are less than 50 years old though. I don't know whether the age of the tree is important or not though. That's just what I see. I planted live oaks when I lived on the MS coast, and they are now 45 years old. There is nary a fern on any of those trees.