A logo question of trademark/copyright?

I recently helped a client with a logo. They were using a copy of the forest service shield with some extra text. They wanted to stay close to the forest service shield, but make it their own and different enough to avoid any trademark copyright issues.

here is the forest service logo

here is the logo I created for them

Clearly we are pushing the bounds here. The shield is the same shape. The tree is very similar. They wanted it close. Today the called me to tell me a forest service officer called them and left a "friendly msg" saying they will need to change the logo because it will be a problem.

So my question is. -Do you think their logo is sufficiently different that it is not a real issue. Obviously a ground officer is not a lawyer and though he might not approve, that doesn't mean hes right.

-If we should change it, do you think replacing the tree and/or the F S would be enough?

Thanks!

EDIT* I am not a designer by trade, I work in film and tv so i'm not as well schooled in design issues.