Heat output per pound does in fact vary somewhat by species. The main component of wood is cellulose, which produces the same heat per pound for all species. But wood also contains lignin (a polymer that provides structural integrity) and "extractives" such as resins. Lignin and resins produce more heat per pound than cellulose, and the lignin and resin content tends to be higher for conifers than for hardwoods. As a result the heat output per pound is slightly higher for Douglas-fir than for oak. Of course Doug fir has a much lower density, so a cord of oak contains significantly more heat than a cord of Doug fir, but on a per-pound basis Doug fir is a tad better. That said, I much prefer oak. Oak produces more heat per cord, and has better coaling properties. And of course there are other hardwoods that are even better than oak.
I love living in the Pacific Northwest, but the quality of (readily available) firewood is better elsewhere.
Doug