Here are all the barks I ended up creating for all the tree variants across all 5 Open World levels of Shadow of War. There was lots of re-use of these between levels and even eventually to create the canopy textures, bush branches, etc. The bark was always the starting point for me when I started on a new tree as lots stems from it.
I used photosourcing techniques on this with heavy cleanup for PBR. I also used Zbrush to generate a clean heightmap and a clean-reading normal map, focusing on large shapes (baked in Substance Painter). Any finer detail was generated with nDo/Photoshop at the end. With this workflow, turnaround time for final-ish bark could be 0.5d-1d, depending on complexity. Was even able to use tessellation/displacement on the trunk for the PC version of the game!