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I suspect that tree grew with something else twined around it. That something else has meanwhile died or been removed. Bittersweet is a likely candidate for what might have wound around the tree ...
Answer
#1: Attribution notice removed
by
System
·
2020-06-03T15:54:24Z (over 4 years ago)
Source: https://outdoors.stackexchange.com/a/16868 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/