I see that some artificial vanillin is made from lignin, but I don't know whether natural wood decomposition creates vanillin. Do you have a reference for that?
https://www.sciencedirect.com/science/article/pii/S134035400...
https://www.jstage.jst.go.jp/article/jjfs1953/37/7/37_7_298/...
> vanillin was also detectèd as a product of wood degradation by some other wood destroying fungi.
The levels of vanillin in waterways (14mg per liter) are ridiculously high for human urine to be the sole source.