When to fell/chop down trees for hugelkultur?

I hope I can explain (:
To my limited knowledge, trees prepare for winter freeze, by limiting water uptake. They increase their salt to water ratio, to achieve lower freezing temperature (might be wrong here). For my location, logging happens between 9/28 to 3/02 when trees are "driest". It is followed by 3/10-3/15 - last froze date. Roots pump water for a month and then they leaf out (3/30). I used to collect all wood needed for my hugelkultur projects but this year I ran out of sources, and decided to chop down some trees. I cut down 3 plane trees, 8 poplars and many insignificant others. When I lifted up each log, magic to my eyes, water started to pour down, like a small spring. I am planning to cover the pile with thick plastic, to block light and create a micro-environment to aid decomposer to set in.
So here I am wondering, does natural-water content of logs somehow affect decomposition speed? Which wood is a better choice, wood that cut in mid winter when it is driest or early spring when it is wet? Or it is insignificant, since hugelkulter is already a slow process?
Or should I leave them uncovered to dry out?  

It seems like it would make most amount of sense to cut them when they have more water naturally in the growing season.  but when they are active, then they might have lots of new shoots that will need to be coppiced too, but if you want these new shoots for the next generation of trees, then you might want to cut them when they will be most active in producing new shoots.    Some people cut in the winter simply because they are less busy then in the summer.

Interesting discussion!  I would like to know if it really makes much difference from a hugel culture point of view.  A forester friend of our told us to cut in the fall or winter when the trees drop leaves if we want to use the wood for firewood as it would have less moisture and dries faster for firewood.  So the opposite would make sense for hugel culture, cut when the trees have higher moisture.