Elm would be my guess...
Have you ever attempted to split elm as fire wood?
Twisted grains...
I used to have a large elm in a veggie garden... digging through it's roots each year was a bit of work...
Something they didn't want resprouting from. The scoring and drilling looks like what we do and then apply glyphosate. Are there any Maples or Oaks nearby? Look at the surrounding trees and compare the lower trunks.
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