I'm burning dry but punky Hackberry and Maple right now. It had spent a couple years outside in the elements, and another year in a woodshed. It's dry and I have no trouble lighting it up, but it's burning very fast and not putting out as much heat as I like. It all depends on the species. S0me types of wood cannot be left out in the elements or it gets punky real fast.
I'm assuming that fungus is the culprit here that gets into the wood and starts sucking out the btu's. What about spraying a woodpile that's exposed to the weather with a bleach solution to stop fungus? Could that cause any other problems? Bleach is cheap, you just need a sprayer equipped with rubber seals designed to handle the stuff. I've sprayed roof areas with bleach solution and successfully killed moss that was causing trouble. Why not a woodpile?