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Fascinating. It looks a little like knuckles. And, did it change the bark? In the later pics it looks less smooth than in the first. ... I'm glad the tree is doing well.

Right after the lightning I took a photo (the second one), its not very visible, but the bark looked quite burned on the spots, if I touched it it fell off into ash. Bark on the burned spots started to fall off in pieces during the winter and now the tree looks very wounded and when I touched the burned parts it was not falling off anymore. A few new green leaves on top tells me its still strong and it survived the winter.
I'm really fascinated by the strength of plants.