Fantasy Demographics

[Xeviat]

Will do.

Anyone else have more thoughts on this?

[Bill Volk]

Mushrooms need food - their energy comes from whatever they grow on. So unless these are magical mushrooms, just having mushrooms doesn't solve your energy problem. A completely sealed, lightless "realistic" ecosystem would need plants that get energy from the earth's heat. I think a few of these actually exist in the deep oceans, but I don't know of any underground ones.

For orcs, you could always do what they do in Warhammer and have orcs that don't need to grow food because they themselves are weirdo plant/fungus symbiotes.

[Polycarp]

"Sealed" being the key word there.  No settlements save for experimental scientific ones have ever been designed to be "sealed" - unless they're under siege, which presents its own problems.  Unless having a dwarven biodome is necessary to your adventure, I don't think there's anything wrong with, say, a dwarven delving depending on above-ground farms and villages just like a castle would rely on the productive land around it.

Of course, if you're going the Underdark route, where the world beneath has its own self-sustaining ecosystem, some kind of magical/pseudo-scientific handwaving needs to be done.  Plants that use earth energy (from magma vents and such) are possible, as Bill Volk said, but there's also FR-style "Underdark radiation" (which has been used to explain everything from metals to mutations and plant growth), for instance.  Maybe there's a reasonably common kind of magic item that produces "real" sunlight, and dwarven fields are dotted with lamp-posts.

[Elemental_Elf]

Mushrooms need food - their energy comes from whatever they grow on. So unless these are magical mushrooms, just having mushrooms doesn't solve your energy problem. A completely sealed, lightless "realistic" ecosystem would need plants that get energy from the earth's heat. I think a few of these actually exist in the deep oceans, but I don't know of any underground ones.

Chemosynthesis is what you're looking for. It's definitely not traditional fantasy but it sure as heck would work.

[Ghostman]

Underground lakes and rivers could play a part in enabling lightless food production. Subterranean streams coursing near volcanic hotspots could convey the heat over long distances, thus providing warmth for life-forms. Such rivers may very well originate from the surface, in which case they'd be providing a continuous flow of nutrients to the underground ecosystem.

[Elemental_Elf]

Underground lakes and rivers could play a part in enabling lightless food production. Subterranean streams coursing near volcanic hotspots could convey the heat over long distances, thus providing warmth for life-forms. Such rivers may very well originate from the surface, in which case they'd be providing a continuous flow of nutrients to the underground ecosystem.

With Dwarves' mastery of stone and metal, it would be quite cool to see them build Aqueducts that dead-end in the foothills of the mountains.

[Xeviat]

Thanks everyone, that gives me some great ideas for dwarven ecology. I'm imagining a group of dwarves that are particularly close with the nearby human kingdom, so close that they have built aqueducts to take the human sewage and garbage away to underground lakes, where the organic waste is used to fertilize mushroom farms. These mushrooms are then fed to the livestock that the Dwarves eat.

[Bill Volk]

Another thing to consider: do these dwarves use fire to cook food and such? If so, how do they vent the smoke? If their underground environment is really deep, air circulation might be a problem as well. I don't think that mushrooms poop oxygen the way plants do.

[Xeviat]

I actually decided that my subterranean dwarves will have already figured out steam power, using geothermal vents and coal to power fans to ventilate their deep citadels. So that shouldn't be much of a problem.

But it is a problem for other worlds. I've seen drawings of dwarf caverns with ventilation shafts, but I don't think a shaft is really going to draw that much oxygen down or remove carbon dioxide (CO2 is heavier than 02 after all).

[Polycarp]

Well, you don't need steam power to run a pump.  In the middle ages, oxen/cattle were used to pump water by hooking them up to a treadwheel around a central shaft (which was then attached to a pump, maybe an Archimedes screw).  The same principle could work for air; a simple two-gear transmission could make the fan go much faster than the oxen (and not much torque is necessary since you're only moving air).

[Nomadic]

Well, you don't need steam power to run a pump.  In the middle ages, oxen/cattle were used to pump water by hooking them up to a treadwheel around a central shaft (which was then attached to a pump, maybe an Archimedes screw).  The same principle could work for air; a simple two-gear transmission could make the fan go much faster than the oxen (and not much torque is necessary since you're only moving air).

Well if you have steam power no reason not to use it, well unless you've got lots of slaves. :P

[Xeviat]

I figure that steam power would probably be more efficient in the end than the amount of energy that would have to go into producing the feed for the oxen.

An air pump is something you're probably going to want to have running at all times, unlike a water pump where you could get away with only having it on when you need it.

[Bill Volk]

And a steam engine requires fire, which requires even more oxygen and makes even more smoke...

[Bill Volk]

If your dwarves are really advanced and have a lot of underground water sources, they could break water down into hydrogen and oxygen through electrolysis. But once again, this probably requires burning something to get energy, and all the excess hydrogen creates the risk that everything will suddenly explode. Even worse, it'll make their voices all squeaky.

[Polycarp]

Or take the more simple route with water and set up a waterwheel to power the fan/pump.  Any underground river will do.