Regarding that sawdust pile never decomposing, was it hardwood or softwood dust? Maybe I'm wrong (feel free to let me know) but don't most hardwoods have some nasty compounds in them that softwoods usually don't? For example, oak and similar woods contain a lot of tannin. This might also explain:
Around my area I've run across a few old sawmill sites while exploring, dating mostly from the late Thirties up to the early '60s. A few have massive sawdust heaps, all pine - D Fir - spruce, and while they definitely still stand out trees will grow in them, mostly poplar. I have a theory on why they don't decompose well - they sit so densely that oxygen can't penetrate them very far, so bacteria can't break them down. On the other hand, I've seen small piles of planer shavings and chainsaw chips (same wood) completely disappear in two years.