Personally I think Wurm got trees right. They naturally spread from trees of the same type to any terrain suitable for tree growth, and they can be planted using sapling. This is realistic, trees are not a rare commodity that people would fight over except in climates where it is hard for them to grow. They spread on their own, and can be grown by men as well. There are plenty of forms of resources worth fighting over that can be introduced before wars, I can't see a reason to make trees one of them. Who has ever heard of a war over lumber in a temperate/forested region?
Also tree-regrowth should be unrelated to stumps. They make an ugly mess. I personally went around destroying them before I realized they were where trees regrew. If they were made unrelated to tree growth, I could continue destroying the ugly things without destroying our future lumber supply.