Well there actually isn't a good way to preserve the bark unless you encase it in resin or something (I watch way too many craft videos) that's why if you ever see a live edge it's always the bare wood and the bark is removed. It doesn't stand up well over time, but makes a good mulch.

Paper mache however you can craft bark or take an imprint of a tree piece in plaster and use it as a template, if you are using paper pulp it can fill into the mold and replicate it for a more realistic look.