After hearing a fellow Bay 12 forum poster say there is no real reason to dig past the first cavern level because the caverns are so similar, I decided to make this. It is a simple mod that aims to add more diversity to the underground caverns, making the three layers more different. Right now it only encompasses plants, but I plan to expand to creatures and fish later. For the current version:

Added 7 new plants that can be gathered from the underground, but only on the lower caverns. Because of this, the seeds can not be bought from the dwarven caravans; you must have herbalists go collect them from underground. There are 4 edible plants(some require processing first, like sweet pods and cave wheat, while others can be eaten immediately like plump helmets), as well as a new dye plant(which doesn't have seeds; that is not a bug) and a plant that can be processed into a very potent poison.

I also changed the value modifiers on the underground trees, so wood from the trees in the deeper caverns is worth more than the ones on the upper caverns.