I have a small patch of ground (15x30) I've cleared for use as a firewood cutting & storage area. I'd like to keep the vines, saplings, etc. from coming back. I don't have the money to pave it, or even gravel it yet. It's surrounded by trees I want to keep.

Anyone know of an herbicide that will kill the small stuff, and keep new from growing back, while not harming the trees?