Sounds nice! Few suggestions:
The day before a tree falls, it should have a crack in it's trunk so you could avoid it. Also it should make a cracking noise.
You should be able to gather nestingmaterial and nuts from fallen trees but once they're empty, they're empty and will disappear.
It would take 10 days for a fallen tree to despawn. They despawn faster if you collect from them. Also if you collec all they have to offer, they despawn during the next night.
Armored body would protect the nicheling so it would only take damage from the hit. It would still be stuck under the tree and it would take damage every day until the tree despawns. Also it could protect baby nichelings by standing in between the tree and the baby. Stones would do the same thing.