What Damaged the trunk of the trees?

What kind of tree is it? My suggestion would be to take your pictures and a sample of the bark to your local extension agent. They should be able to help you. Good luck.

I would either have an arborist do a consult or contact your local university agricultural extension program to deter what the disease/pest is and the appropriate treatment if it can be saved.

Could be sun scald on the younger thin tree trunk. Try painting tree with white paint. The larger tree looks like it's dying/already dead.

Where in Canada are you?

Alberta

I believe any acrylic water based paint is fine - but just to be sure, ask a nursery worker. If they don't know, google it. Orchard growers do it all the time for their trees.

These may need tree pruning and painting the stump of the tree to protect it from snow and direct sunlight.

I'd rethink the gravel near the trees-it tends to retain and reflect heat, excessively, requiring much more water in hot weather. Try switching to a hardbark mulch or pine needle mulch, either of which should retain/reflect far less heat. You may also pull back some gravel to see if any insects are hiding nearby.