The Tradition of Man vs. Nature
Literature has a rich tradition of man versus nature, The Call of the Wild, Hatchet, and dozens more titles of survival in the face of a hostile wilderness. These stories revolve around personal resolve, knowledge of how to survive in the wilderness and many incorporate communion with nature and spiritual themes. Standing alone in a pristine wild place can easily engender this sense of wonder and awe with everything that is nature. The theme of man versus nature is also very much alive in popular media with shows like :shudder: Survivor, Man vs. Wild with Bear Grylls, Ice Road Truckers, Ax Men, and so on.
But the common theme of nature today is protection and conservation in the face of our destruction and exploitation. It would be easy to project this onto a basic fantasy setting, elves oppose the woodcutters in a replay of loggers and tree conservationists, druids protecting wild animals from poachers and hunters. This does a two disservices to the genre. The first is that it brings 'serious business' into what is supposed to be a venue of entertainment. This isn't uncommon, many adventures and encounters are based on often Aesopian moralism. Why else would there exist monsters that look like treasure chests, and monsters that exist solely to destroy specific things. Dont get greedy, or the treasure monster will try to eat you, and so on. The second reason is that in the fantasy genre the forces of nature are much more dangerous, intelligent and certainly competent.
Of the Trees
Call it an ent, treefolk, treeking, treant, it is a walking talking tree. A tree is a large object, its harder to cut up and harder to burn than most people will give credit to. Forest fires are more an issue of poor land management than trees being made of explodium, and cutting trees is dangerous today with industrial machinery and chainsaws. Being in a fight with a sixty foot oak tree is going to be an epic encounter. This being said, the treefolk have a vested interest in protecting the forests, along with things like dryads, forest spirits, and denizens of the forest who are responsive to said powers. A treefolk leader could call together allies and put an end to a small or medium sized incursion into a forest and turn a major incursion into an open war with the forest.
Of the Druids
In a similar vein druids represent a semi-religious semi-militant faction with a vested interest in maintaining the protecting wild lands from almost any sort of development. Druids can range from peaceful conservationists who teach responsible coexistance with the land, favoring horticulture over expansive agriculuture, to the militant terrorist who leads hosts of animals and monsters to attack settlements and projects that they deem offensive.
Red of Tooth and Claw
Another common theme is protecting animals from mankind. In the fantasy setting there are animals that are much more dangerous than mundane beasts. Hippos, pandas, black bears, and other seemingly non-threatening animals regularly kill people. Before the advent of firearms, harpoons, and massive ships, hunting for animals was rarely done for sport as it was inherently dangerous. Without our technology of the last two centuries the playing field between man and beast is much more level, and even factoring in magic and magic weapons this is easily balanced by animals having their own innate abilities and powers.
The Elemental Factor
In my personal setting, elementals exist as the technicians, mechanics, and janitors of the ecosystem. Many of the conflicts between elementals come from conflicts of interest between their charges. What has priority? A swamp or a clean draining river, or the forest on the edge of the area? Most elemental duties go unseen, managing air currents, oceanic currents and balancing the forces of earth and fire against each other deep in the earth. Should a human endeavor reach deep enough to draw the notice of the elemental courts, the humans in question could and would certainly draw the attention and possible ire of the elementals themselves. A deep enough strip mine in a fantasy setting would bring earth elementals up to the surface to stop the destruction, while enough waste dumped into a river is going to really cheese off the spirit of the river.