There have a been a few long threads on this in past years. Here’s one from 2020:
https://lists.openstreetmap.org/pipermail/talk-us/2020-June/020215.html
The outer boundary of the US National Forests is the “proclamation boundary” where congress has authorized land acquisition, whereas the forest-service-owned lands are where public use is allowed/controlled by the Forest Service.
Paul White said it well:
However, doesn’t that [mapping both] violate “one feature, one OSM
element” ? I
believe we should stick with the inholding method, because separating
national forests into different relations complicates search features,
rendering, etc.For most users, the proclamation boundary would be pretty useless if
ownership is already there. As Kevin noted, the proclamation boundary shows
an area that the government has been authorized to acquire land, and has
little impact on actual protection and land cover.
I believe the result of that and other discussions (such as in the #protected-lands channel of the OSM-US Slack) wrapped up with the consensus that only the ownership boundaries would be mapped for National Forests and BLM lands.