Why do deer's eat bark?

In the winter, all the leaves fall off trees, and grasses and herbs die and are covered with snow. Deer will also eat all of the vegetation out of a forest, so the bark is the last thing they have. Why do deer's eat bark?
Its deer, not ';deer's';. They eat bark so they won't die of malnutrition and starvation.Why do deer's eat bark?
Deer eat bark when there isn't anything better to eat so they won't starve.

what in your opinion is bes c ide and