This is in one of my favorite fortresses. I embarked on a frozen arctic wasteland of a mountain range, with no vegetation and no surface water that isn't frozen rock-hard all year long. A howling devastation, which was just fine for my band of paranoid isolationists. They dug down to the cave river and began building Paradise. Over the course of the next decade they hollowed out an enormous series of galleries along the east shore of the river, making a fine forest of tower-caps and underground herbs. Metalworking wasn't really a priority for these dwarves, and they'd bought enough wood off of passing caravans (or, initially, collected it once the caravans perished from being locked out in the freezing waste) that there was no need to harvest the trees; the goal was largely just to have a nice place to live underground. They never cut a single tree down.
Eventually, though, an elven diplomat comes and starts making complaints about how the dwarves are butchering trees. "This one's even crazier than the rest of the elves," the dwarves thought to themselves. "No trees
existed here until we came along. But, just a moment now. It's so crazy it just might work... The middle and upper galleries, sure, we walk through there all the time and it's lovely. They're carved out of marble and mica, a work of art to behold. But the lower gallery is carved out of granite and nobody ever goes down there. And the rubble heaps are full of waste marble and iron ore from when we carved out Magnetite Hall. How many axes do we have to spare...?"
Once the dwarves got seriously going on their steel industry it became an addiction. Everything's steel, and the lower galleries are a continuous rolling clear-cutting operation. Good idea, elves!