I wouldn’t call tunnels a biome though. That’s like saying a cave in a tundra biome on Earth is its own biome. (Is it? I’m not even sure. First instinct, no.)
caves are definitely their own biomes, they have totally different environmental conditions and will see life evolve specifically for them. There’s even biomes within caves, the entrance which is bright, the twilight zone further in, and the pitch black inside.
I wouldn’t call tunnels a biome though. That’s like saying a cave in a tundra biome on Earth is its own biome. (Is it? I’m not even sure. First instinct, no.)
caves are definitely their own biomes, they have totally different environmental conditions and will see life evolve specifically for them. There’s even biomes within caves, the entrance which is bright, the twilight zone further in, and the pitch black inside.
I only found one classification that includes caves/cave systems, but I guess it passes.
Source: https://en.wikipedia.org/wiki/Biome