Originally Posted by
DrTimPerkins
After a fairly cold spell, the water in the stem will be somewhat depleted due to sublimation of water vapor out of the branches into the air, so the moisture content in the tree starts out low, so flow will be minimal the first time or two there is a thaw. The soil in the woods rarely freezes solid more than a few inches at most, but if the snow is packed around the stem of the tree, the stem will be solidly frozen and water in the soil cannot be pulled up into the stem and branches until there is enough melt to get the snow away from the stem a bit. Once this happens, during a freeze water will be drawn up into the stem and branches and will flow out the next time there is a thaw. Kind of like priming the pump...it takes a little while for the process to really get going well.