One of the most theraputic activities I can do is stacking the winters wood. Here in the Northeast, trees grow almost like weeds. If a pasture is neglected for a few years, it will quickly be taken over by birch and poplar. Later, this will change to pine, oak, beech and other healthy, mixed forest types.
As I'm stacking wood, my mind wanders over things I've wondered about over the years and, sometimes, the answers appear.
Building a proper woodpile is an art. Each 16" long bolt is a piece of a puzzle. It has to be twisted and flipped to match the row beneath it. The ends should be aligned to show an even aspect. Shorter or longer logs have to be matched with the row behind. Splits are arranged to expose the maximum surface area but not leaving obvious gaps. Packing density is desireable, but drying is important with green wood. It's nice to have a tall shed to minimize floor area, but too tall and the pile becomes dangerous. The end of the row needs support. Either a sturdy wall or a criss-crossed stack on the end, perhaps slightly biased inward to resist outward forces is needed.
One of the sad sights we see is a stack of wood someone has invested much labor into, fallen outward and collapsed. It has happened to me and most recently, to a nephew who had to have some large red and white oak taken down.
Now, I know how that happens. The answer, obvious now, is differential drying.
As wood dries, it shrinks and cracks. Drying is affected by relative humidity, direct sun and wind or air movement to carry away the moisture. If I have stacked three or four rows of green, undried wood, the exposed ends will dry faster than the inside rows. The closer the stack is to the outside, the quicker the moisture content will go from perhaps 60%+ to 12% or so water content. As the wood dries, the ends get smaller and the top of the row, especially if it is tall, will slowly ratchet outward. That then exposes the ends of the next row to more drying air and the process of movement proceeds.
This isn't an earthshaking revelation. It's probably been written up in some Mother Earth News article but asking the question "Why" and then coming up with the answer is quite satisfying. Perhaps there is another answer, but this fits my observations.
Earle Rich Mont Vernon, NH