When I was making a new world with custom settings under the "Forest" and "Caves" tab, I saved it hoping to use it again for another world should I start a new one. However, upon starting a new server, my first preset disappeared, so I recreated the exact same preset, but instead of being saved as "Custom Preset (1)", it was saved as "Custom Preset (2)" as if the first one existed, but didn't want to show up. Sadly, I have more to say. I started another world again and Preset 1 reappeared, but Preset 2 disappeared. I'm sure they both exist, but can't both appear. This may be an issue if one plans to make a third preset. I just wanted to point this out since many DST Players may save different settings, but not be able to access them due to their reoccurring disappearances.
Make a world and adjust the variables under the "Forest" and, or "Caves" tabs and save it. Start the world and exit to make another world and try searching for the preset you have saved. You may see it is not there. If desired, recreate the same preset and save it. Repeat starting a world and exiting to start another world and see that "Custom Preset 1" reappears, but "Custom Preset 2" has disappeared.