I am sorry for this delayed reply to your gardening question. We are transitioning to a new Q&A system and your question was unfortunately lost in the transition. I have discovered it now and hope this reply is not too late to be of help.
If what you are describing is on the trunk, no that is not a concern. Moss and lichens do not draw energy from the tree but only use it as an attachment on which to grow.
Thanks for the question. Please stop in again soon!
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