Pat's got that one fielded, for sure, but there are types of pine that can be used from what I understand. I just got The Encyclopedia of Native American Bows & Arrows and noticed that one of the northern Canadian groups used a pine bow and have heard of it used elsewhere, I think like Siberian areas and such.
I've been real curious about the Southern Yellow Pine and Slash that grow down here. They're supposed to be pretty dense. Don't know though.
I'd love to see some true pine bows.