Pine can be incredibly elastic, given the right thickness. It looks like you've figured out what that is. That's a nice looking bow, and it's good cheap tillering practice.
I've always wondered how hemlock (Tsuga Canadensis, not the poisonous weed) would do, If I remember correctly, the specific gravity is only about 0.45, but it was truly evil wood to frame with. My dad would have it sawn into rough framing lumber and barn boards, saving our rare spruce and fir for planed finish boards. Compared to lumberyard framing, it was heavy, stiff, and difficult to drive nails into.