That looks really cool, maybe they are thriving because they support each other (physically, food-wise, shelter). Maybe plants are happier when they are together like that.
I think that the physical support might have something to do with it aye I'm expecting that after a couple of years that they will fuse together into what's pretty much one plant, sharing the xylem and phloem etc... who knows!
Well maybe someone on here does, anyone done/read anything like this before?