Tree trunks are subject to wildlife predation, especially when normal foods are scarce. Tasty saplings are particularly vulnerable to rabbit and deer nibbling. To escape injury, a tree trunk must be completely encircled by an object that can't be penetrated by the teeth of hungry animals. While rabbits only damage the lower 2 feet of a plant, deer can reach food 8 to 10 feet above ground.
The simple solution is a tree guard. There's a wide variety of products made specifically for this purpose, but they can be pricey. Recycle plastic jugs to make no-cost tree guards, and stack them as high as the lowest branches--no matter how tall the tree.
Use sturdy scissors to cut the bottom 1 inch off of a clean empty plastic milk jug. Cut 3 inches off the top of the jug, as well.
Turn the milk jug tree guard upside down. Slip it over the top of the sapling and move it all the way down to the soil line. Position the guard so that the handle faces the prevailing winds. Push it into the soil and work it several inches deep to add root protection against voles.
Slide the dowel into the guard and down through the handle of the milk jug. Work it about 6 inches deep into the soil.
Stack more tree guards on top of the first one if it's not tall enough to completely protect the trunk of the tree, right up to the foliar canopy if necessary. If rabbits are your biggest issue, then protection 2 feet above ground level will be sufficient. Deer can reach as high as 8 to 10 feet by standing on their hind legs, so taller specimens should be guarded accordingly.
Add more tree guards to the stack following significant snowfall because rabbits are light enough to stand on top of snow without sinking into it. That means you'll need to protect tree trunks an additional 2 feet higher than the surrounding snow surface level to keep them out of the reach of rabbits.