My neighbor had his land logged off and the crew dropped some big red oak over his property line onto mine, and left them where they fell. Neighbor didn't want them so I hooked on to them and hauled them out. They laid there for almost 5 years, cut off from the stump,with tops still on. Some of the bark had fallen off but most was still attached. If it wasn't for the fact that bare wood was showing, it was hard to tell that they had been down for 5 years. I cut them up and found absolutely no rot any where in the tree. Some of the best oak I ever burnt. Split easy and was dry enough to burn quickly ( 6 months stacked). The limbs were bone dry and solid. You could tell the difference between the trees being held off the ground by the tops and laying on other trees, and the ones laying on the ground, by a wide margin. I frequently drop hardwood trees and leave them to be picked up later. Sometimes it's a year or more before I finally haul them out to the landing. Never had one rot or get punky yet, and a surprising amount of moisture has been removed by the time I process them. Pick up a 4 ft. stick of fresh cut wood and compare it to a stick of downed wood, of equal size and species, and you can tell the difference. The key is no ground contact, and most times the tops left on the tree takes care of that.