On the ground,...depends, it will likely still have some BTU's left in it. Question is, is it worth the hassle/handling. Depends on whether it is "on the move" (your bugging out) or if it is in your BOL (my case).
Inner bark of a poplar/tulip can be woven into cordage. Can be somewhat dead. The one I used the bark on the big trunk was able to peel away, so likely a little dead.
I have a woodlot (10 of our 20 arces), and I do occasionally cut deadwood. I mostly have it hauled in by urban tree trimmers, or by my truck. I have ALOT of old saw logs laying that I will be "cutting to firewood length" while fuel/oil are still available. This is on my short "to do list". I have enough t oheat my home and shop for....probably 3-4 years laying around. I can always split it by hand if necessary, but the fuel/oil could be an issue during any crisis.
I am also, preping my fields for "cropping" if necessary, got a manure spreader and have been hauling in horse manure, and the tree guys bring me tree chips which will also add some nutrient once they begin to decompose just under the surface (disc them in).
We try to maximize EVERYTHING around these parts, even the stuff others "cast off".
Good luck.