It’s hard to find official documentation (no surprise there), but there are many stories of Germans in WW I and WW 2 adding sawdust to their bread mix to make it go farther. The sawdust was called “tree flour”.
Perhaps everything old will be new again.
https://www.quora.com/Is-it-a-myth-that-some-bread-was-made-with-sawdust-as-a-filler?share=1
Pine bark has been used to make bread for centuries. Several other types of bark are edible, but pine seems to be the most popular, historically.
Make flour from acorns...need to soak in water a couple of times to get rid of the tannin...staves off starvation...also pine seeds are nutritious...and many wild plants are nutritious...cabbage and others...but be careful of wild carrots as are toxic.