They do function, but for a lot of things it will seem like they don't work because many things can't be found there.
Example: in Mountain biomes, even though it may say on embark that vegetation is abundant, you will find no vegetation. The only exception is at the very edge, where Mountains meet some other zone. There Mountain biome things can be found, because the between-area is still considered mountain but has non-rock soil on which they can grow. The problem with Lava and Chasm is that these biomes, which do not place plants during generation at all possibly because they are entirely rock and thus do not support them, often do not border biomes or soils which can support plants. They are, however, active: if an entity can use subterranean plants, it may bring these along for trade, or bring wood of trees with Chasm, for example, for trade. We know these biomes are functional as well because creatures, which are generated in these habitats, with the tags will appear in the propper place (lava puts things in lava places, chasm in chasm places.)
So it's not that they don't work, it's that trees are not coded to grow on the solid rock substrates of Chasms and Magma. I had the same problem with plants I tried to get to appear in chasms. WHat ended up being the compromise is giving them other biomes so they can be collected, or trading for them, and then growing them in the chasm or within the vicinity of the magma chamber, in gardens. Sure enough, when these are their only biome tokens, they can be grown in these habitats, and not otherwise. They will not, however, be able to spontaneously generate there the way other plants do on soils or the way sub_water plants do in indoors mud.
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Topic: Which SUBTERRANEAN_ biomes are functional? (Read 1174 times)