Thinking Really Hard About Trees As Tall As Mountains

I have written semi-regularly about the concept of a megadungeon inside an impossibly large tree. (See here, here, here, here and here.) Recently I tried to do some calculations to figure out, essentially, how tall such a tree would have to be in order to have, say, 10-12 'dungeon levels' of 30-50 chambers or more each tunnelled into its trunk.

The answer is: really tall.

Googling around on the internet it seems that 80:1 is a rough rule of thumb for the height-diameter ratio of a stable tree. This will obviously vary between species (and many environmental factors). This means that if a tree is a mile high (meaning a mile from the base all the way to the top of the crown), the diameter will only be about 22 yards and the circumference just under 70.

That's really not very thick if you want to imagine that human-sized tunnel networks are burrowed into it. You're talking essentially about having to fit each dungeon level roughly into a 22 x 22 yard space (yes, I know the area of a circle isn't the same as the area of a square - I'm just using rough figures).

For a mile high tree, then, it isn't realistic to think of the dungeon levels as being sprawling networks of chambers and corridors as a subterranean dungeon would have. Each level would have to be smallish, or maybe with lots of small rooms, or very dense (meaning the rooms are compressed together with only short distances between them), or all three. Or scale would have to be achieved by each dungeon level mostly being spread vertically rather than horizontally - which is hard to map.

For a ten-mile high tree, of course, it's a different matter. There, you are definitely in 'traditional megadungeon' territory in terms of mapping. A tree trunk 220 yards in diameter and just shy of 700 yards in circumference can fit a heck of a lot of dungeon into it. But then one runs into a different problem - figuring out how to map it.

Previously, I argued for using Excel for tree-trunk mapping (see here). The basic idea here is that you imagine the surface of the tree trunk as a 'wrap around', like sections of a cylinder laid out in 2D. You can then plot out where the climbers are on its surface at any moment like in Battleships:

Imagine the above map shows a cross-section of tree trunk measuring 500 x 700 yards, assuming a 10-mile high tree (whose circumference, remember, will be just under 700 yards). Each square here represents a 50 x 50 segment of tree trunk surface. Fine for the circumference. For the height, assuming that the tree trunk is probably half the height of a tree from base to crown, we would need roughly 15 (rather more really, but we'll keep things easy) of these cross-sections to make it to 5 miles, given that each such cross-section as a height of 500 yards.

That is a lot of map, but it is just about workable. It suggests that a way of presenting a megadungeon inside a 10-mile high tree would be to break it down into 15 cross sections of 500 x 700 yards. Each such cross section could have burrowed into it a 'major' dungeon level of 30-50 chambers (perhaps with some sub-levels), together with other mini-dungeons and monster lairs, as well as things like wizards' dwellings, villages, druid temples, and whatever other adventure sites you were to come up with.