Possible to apply physics to certain joints/bones only?

I think I have an idea of how to get my “bending tree” to work (I posted a question about that recently). Basically, I want trees in my landscape to react to nearby explosion forces. And rather than just blow away like solid objects I’d want the tree to softly bend from the force. Pretty much what strong wind does to trees in reality, but stronger.

I could show you pictures of what I’ve done but it’s pretty simple. I have a cylinder with eight bones in a tail. With some gravity, mass scaling and spring adjustment I think I can get the tree skeleton to behave somewhat realistic to impulse forces.

Now, the problem is obviously that the tree simply will fall over if I apply an impulse to the skeletal mesh. The tree structure might bend on it’s way down and all, but it will fall over. Is there a way to not apply physics to the root bone, but have the rest of the bones in the chain to use physics?