SHISHIGAMI WILL POKE YOU TO DEATH
DO NOT REMOVE HEAD
>:C
Anyway, I think the wildlife bit is already in the works or will be in the future. I agree though, as certain conditions decline - total trees, total shrubs, total grassy tiles, total water - the wildlife population should decline. (More specifically, it should repopulate more slowly until the environment reaches a point where repopulating for certain animals stops.) This would make conservation a big deal for people who like for their dwarves to hunt and fish. If an environmental health factor were put in that effects how fast trees and shrubs regrow as well, it could very well effect the economy of your entire fortress. Isn't pollution planned, which would have an effect similar to this?
As for the forest spirits, elves can already launch attacks on your fortress if you violate a tree-cutting quota. There should be other denizens of the forest that take offense to your logging, though. Not just lurking wild predators, no. Ents - Tree-Men as the game might call them - would be wonderful. Dryads could tack themselves onto certain trees and attempt to ward off anyone who tries to cut them down. (Magic would be preferable here.) Both of those could be inhabitants of 'good' forests. As for more general forest hazards? Bees. I've suggested massive-ass bees before, but seriously, what if you disturb a random tree and it spawns a few swarms of bees that cause injury to nearby dwarves? That'd kick ass. You could even trap them and set up an apiary. I suggested a few nasty things that might appear in an 'evil' forest, also. (Killer murkwood trees, giant flytraps, etc.) Undead ents could appear in an 'evil' zone too, which would make logging in those terrible places even more horrid than it already is.