Japanese Red Maple bark has fungus on it
It is probably moss or lichen which to not cause harm to the tree. This is more common in shaded conditions.
For information on lichens, please watch the following video:
https://extension.psu.edu/do-lichens-cause-harm-to-trees. Detailed information is addressed until the 3:10 mark in the video which then addresses: Do lichens cause harm to trees.
Additional information is available in print at:
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