You guys are likely going to scoff when I say that all dry wood releases about a million BTU's per 132 pounds, but I believe that is the case. However, the species vary substantially in density. The denser the wood, the more BTU's that a given volume will deliver and the less room that it takes up inside the stove or fireplace. Usually, the denser the wood, the slower that it burns because there is less air trapped inside. So, 132 lb of dry cottonwood will deliver as much heat as 132 lb of dry oak, mulberry, ash, hedge, or other hardwood goodies -- about a million BTU's.
Now I will start to duck as the raspberries and eggs are thrown.