Once upon a time, I thought about having wilderness difficulty scale up and down sort of like dungeon difficulty. I think that proposal had several problems, but I think maybe I see a better way to do it now.
I've been thinking about how one would/could do low-level wilderness adventures in OSR games. The monsters in wilderness encounters are just so numerous that any encounter is likely to wipe out a low-level party that gets a poor reaction roll and fails to evade, and none of your "win buttons" work - if you cast sleep on the goblins, you drop a quarter of the warband, and the rest will still get you.
Some OSR systems already sort of have a method to adjust encounter difficulty based on dungeon level. It's possible it was in AD&D and I just haven't seen the original source. In OSRIC,
Lesser monsters encountered on a lower dungeon level
should have their numbers increased by the same amount
for each dungeon level lower than their monster level. For
example, the sub-table # column lists 2d10 for goblins (1st-lvl)
encountered on the first level of the dungeon. If encountered
on the third level of the dungeon, they would be three times
as numerous (6d10).
ACKS has a similar rule, with a different constant:
Roll the appropriate number encountered for the creature to determine how many are present. Increase or decrease this roll by one-half for each step of difference between the dungeon level and the Random Monster table used (round down).
OSE, surprisingly, does not seem to have such a rule, which is part of why I think it might be an AD&Dism.
But if we accept that the number of monsters appearing scales up with dungeon level, then we can argue that the wilderness is something like the 7th level of a dungeon, on the basis that a wilderness encounter of goblins is seven times (on average) the size of a dungeon encounter of goblins. Taking ogres instead, we get something more like a 4th-level dungeon, since ogres appear on the 3rd level of dungeons and an encounter with them in the wilderness is only twice as large as a dungeon encounter. We could probably go through and figure out the average "effective dungeon level" of wilderness from all of the monsters that appear on the "random monsters by dungeon level" table.
Just looking at the table and a few entries instead of doing that analysis, I think something around dungeon level 5 is probably pretty close. Possibly with an extra adjustment for ~1HD creatures that causes them to scale up faster.
If we characterize generic wilderness in this way, as a multiplier on encounter size, then we can alter that characteristic for different wildernesses, just as we do for dungeon levels. This provides another way to create difficulty gradients in pure wilderness like we already have in dungeons - and a much finer-grained one than ACKS' borderlands-vs-wilderness distinction! If you meet goblins in the Sunny Meadow, effective dungeon level 2, you only encounter two gangs, and sleep can still save the day. If you encounter goblins in the Ash Wastes, effective dungeon level 7, you get your usual 2d6 gangs and sleep will not save you.
Characterizing biomes with effective dungeon level also provides a way to figure the size of unguarded treasures (or trapped treasures) in the "wilderness as dungeon" model.
It might also be useful as a starting point for the effective level of the first level of dungeons located in those biomes. If you're in the Ash Wastes and you find a dungeon entrance, the first level is not going to be as easy as the first level of a dungeon in the Sunny Meadow!