If there's no ground contact, and you keep up with a bit of finishing maintenance ( a good oil base sealer ) every so often (it will vary with your location, exposure to the elements etc) don't see why pine won't last well past your lifetime.
The desert is a true treasure for him who seeks refuge from men and the evil of men. In it is contentment In it is death and all you seek (Quoted from "The Bleeding of the Stone" Ibrahim Al-Koni)
