Hello, happy to help.

Your closeup photo of the needles don't show any black spots on them which would indicate a fungal disease.  It's possible that disease didn't kill that part of the tree.

Since I can't zoom in to your tree's profile photos to see whether there is evidence of separation between the dead side and the living side, you might look to see if the trunk on the dead side has been girdled (bark removed all around its circumference).  If that's the case and the live side appears to still have access to water and nutrients from the roots, then you could cut off the dead side without hurting the live side to watch it grow.  Since it's so small, it has a chance to straighten out as it grows.

Voles and rabbits are the chief culprits behind bark chewing in winter.  Until your young trees are bigger and have thicker bark, I recommend installing a hardware cloth fence around your trees to keep them out in the winter.  The fence can be removed once there is more available food  to distract these critters from your young trees.

If you don't see bark chewing evidence, feel free to reply and we'll discuss other possibilities.

Good-luck!

Hello,

It's hard to tell. The white stuff appears to be part of the decay process of the bark of the dead section of the tree along with the decay of the leaves that covered the base of the tree. I don't think it presents any issues for the live portion of the tree.

The bark doesn't appear to have been chewed away. At this point without an in person assessment by a certified arborist, it's hard to determine the problem. A professional can inspect all parts of the tree to identify canker issues, environmental damage, and signs of disease. If you're interested in hiring a professional, here is a link to information about how to find and hire one.

It remains up to you whether to remove the dead portion and carry on or remove the tree entirely. If you should decide to replace it, I recommend planting your new tree a few feet away from where this tree is. The old tree's roots need time to decay and can marginally deplete the surrounding soil of nitrogen during the decay process most of which occurs within a year.

Good-luck!