Ref :
http://i7.photobucket.com/albums/y269/CliffStamp/fiskars/hatchet/fiskars_log.jpg
That stick is at least two years seasoned, so it is really dry, there is no weight to it, I would not even shoulder it to carry it for example, and have shoulder 12"+ sticks like it trivially and stack them all day long.
It is frozen, meaning it fractures violently when chopped and even has ice inside, the grub trails get filled mainly, but the outside can absorb water. It is really bad for fire starting if you get a decent rain + high temps followed by a really fast and sudden drop and everything freezes.
The ideal woods to burn are those that are seasoned and opened, either by rot, or insects (ants locally) which can reduce it to cardboard consistency which you can pick apart with your fingers, you can slice off 1"+ thick sections easily with a knife, but they absorb water like sponges with it rains and get soggy so go from being best to worst.
Yes it is bad to burn, sometimes it is all you have so you have to make due. However the frozen and icy wood dries out *way* faster than actual green wood when split. That bucket in the picture will be bone dry with one day next to a wood stove, only the outer shell is frozen (there is water everywhere in it of course, just not significantly) but if it was green it would be days longer unless it was at least quartered.
Green wood doesn't burn very well here at all unless it is very sappy or you split it really fine, birch is ok because it is fairly clear and you can split it really fine, with pine boughs and birch bark and trunk you can get a fairly hot fire even in bad conditions, the bark and boughs don't hold water or snow, and birch rarely rots or gets eaten by ants so it can be split and used almost anytime, I have seen it otherwise.
Ideally you have no rain, snow or wind, lots of tinder (grasses, bark, lichens) and small dry wood, but who plans for ideals.
-Cliff