Nature Spirit

The Nature Spirit is a mythical being with a direct tie to nature. This includes your standard fairies, sprites, imps, dryads, nymphs, and occasionally even deities. Usually found in Ghibli Hills, and they may be a type of Genius Loci if they're tied to a specific places (frequently a valley or a forest, though dryads are traditionally connected to a particular tree and naïads are tied to a specific body of water).

The exact origin and motivation of the Nature Spirit varies widely. One may be kind and gentle Spirit Advisor living in peace and harmony, or it may be dangerous, uncompromising Knight Templar determined to defend nature against man because Humans Are Bastards. The most extreme example of the latter results in Gaia's Vengeance. They may also be very old, to the point of being a Time Abyss, to emphasize how insignificant human affairs are.

For the human version, see Nature Hero. Mix the Nature Spirit with Anthropomorphic Personification and you get Mother Earth. Occasionally, a virtuous and nature-loving human may be promoted to a Nature Spirit upon death, or when the plot demands it. If there's non-nature spirits for other natural forces, they can make up the Magical Underpinnings of Reality.

This is Older Than Dirt; any of the oldest human myths feature magical beings with a direct tie to nature, such as several cosmic and riverine Egyptian gods.

Anime

 * Princess Mononoke has the deity version of this, though the title character was actually a Nature Anti-Hero who was Raised By Wolf Gods.
 * Another Ghibli example is Totoro. Although only mentioned once as being "The Keeper of the Forest", he certainly shows it.
 * Celebi is this in the fourth Pokémon movie, as well as an episode each of the main anime and the Chronicles spinoff.
 * In a more general sense, most of the Pokemon in general have qualities of Nature Spirits.
 * Tsukihime: the True Ancestor vampires, who were considered to be the perfect existences created by the Earth (in order to defend against humanity's contradiction against nature, as humans are capable of being able to survive after the planet's death), had near-limitless power due to their connection with the planet. Arcueid (the last remaining True Ancestor) is very possibly the most powerful being on the planet... She can defeat virtually anything that comes against her, despite having to use 70% of her power just to hold back her vampiric blood-lust.
 * All over the place in Mon Colle Knights.
 * Many of the demons in Amatsuki are connected to nature, particularly the tree guardians.

Film

 * "The Firebird Suite" in Fantasia 2000.
 * Crysta and the other fairies in Fern Gully: The Last Rainforest.
 * In Hellboy II: The Golden Army, the elf-prince Nuada sends out a forest god against Hellboy & co. It begins as a bean, and grows substantially when it hits the water...
 * Aisling from The Secret of Kells is this combined with being one of The Fair Folk.
 * The nature deity in Avatar starts off in harmony with its indigenous people, but becomes ticked off when humans attack and rallies the forces of nature against them.

Literature

 * The Last Unicorn's title character.
 * All over the place in the Chronicles of Narnia, emerging from the background mostly in Prince Caspian and The Last Battle.
 * The Wraiths of Andelain in The Chronicles of Thomas Covenant are noncorporeal beings that help to safeguard the region of Andelain from harm.
 * In Thomas Burnett Swann's contemporary fantasy story The Dryad-Tree a newlywed bride becomes convinced that the tree in her husband's garden is possessed by a jealous dryad.
 * Tom Bombadil in Lord of the Rings.
 * Mercedes Lackey adores nature spirits, and they appear in almost all her works.
 * Also found in Tanya Huff's Quarters novels as representations of the four quarters (elements).
 * "I am the Lorax! I speak for the trees!"
 * The Dark Tower has the twelve Guardians of the Beams, who manifest as a bear, turtle, lion, hare, elephant, bat, horse, snake, fish, bird, wolf, and rat.
 * And they're apparently cyborgs.
 * It's left ambiguous as to whether the cyborgs are the original spirits (and thus inspired the legends), or are replacements for the beings which departed when the magic went away.
 * Algernon Blackwood was fond of this trope; his variants tend to fall somewhere between The Fair Folk and Eldritch Abomination.
 * Following the ancient Greek myths, there are many nature spirits in Percy Jackson and The Olympians. There are of course dryads and water nymphs, as well as satyrs who are tied to nature as a whole. However, Pan, God of the Wild, has gone missing, so these nature spirits are suffering, and have put their last hopes on finding him.
 * An extremely dark portrayal in Arthur Machen's The Great God Pan: Helen Vaughan is the daughter of Pan, the Greek god of nature. Machen depicts him as an Eldritch Abomination linked to Satan. Don't go in the woods with Helen.
 * The Green Mouse from Robin Jarvis's Deptford Mice series.

Live Action Television

 * Power Rangers Wild Force -- like its Japanese counterpart, Hyakujuu Sentai Gaoranger -- had the Rangers receive the power of the Great Beasts, powerful spirits representing nature and animal-kind, to fight against the Orgs, spirits of corruption and pollution. Gaoranger was more explicit about this, with the Orgs basically being corrupted nature spirits.

Myths and Religion

 * Classical Mythology has nymphs such as naiads, dryads, and gods such as Helios and Luna; all the way up to vast cosmic gods like Gaia (the earth), Ouranos (the sky), Nyx (night), and Hemera (day).
 * Some of the Japanese kami are nature spirits.

Tabletop Games

 * In the Forgotten Realms, Rashemen has a high density of such creatures.
 * One example of such in the computer game Neverwinter Nights 2: Mask of The Betrayer is Proud Warrior Race Spirit Bear Okku.
 * In the Oriental Adventures setting of Dungeons and Dragons, there is a race known as Spiritfolk who are essentially Half Human Hybrids of humans and Nature Spirit.
 * Nature Spirits are what makes the Magical Native Americans...magical...in Deadlands. Such spirits occupy a moral middle ground between The Legions of Hell and The Heavenly Host. In-keeping with a shamanistic magical religion, Native Americans who know how can attract the attention of the spirits and convince them to lend aid.
 * Nature is not immutable, though. Some of the Nature Spirits are still around in Deadlands: Hell on Earth, while some others have been...warped. If you ever wanted to play something called a "smog shaman", now's your chance!
 * The Garou of Werewolf: The Apocalypse consider themselves soldiers on behalf of Gaia, a goddess-level spirit representing Earth as a vital entity. They also consider the Wyld, the embodiment of primal chaos and growth, an ally in their fight -- though, in a bit of a subversion, most werewolves hold the Wyld at arm's length because it can be... unpredictable.
 * In Warhammer Fantasy Battle the Wood Elf army includes Dryads. Who apparently are quite pretty and sylph-like off the battlefield, but when outsiders meet them tend to be horrible spiky tree monsters. And then there are the actual Tree Men. And the sprites used as personal weapons. And the Wood Elf king, who leads The Wild Hunt. On foot.
 * In Nobilis, the Mythic World operates entirely based on these. According to the rules there are approximately a trillion trillion nature spirits in the world - this is a big deal because instead of the universe being "some big uncaring thing you must deal with" it is "a big uncaring people you must deal with" - one can convince a car to keep moving even without gasoline, converse with mountains and many such things. Granted, in most games only the most important spirits play a big role, but just knowing they are there is important.

Toys

 * The Element Lords in Bionicle.

Video Games

 * Samurai Shodown's Nakoruru became one.
 * So did Aeris, according to some interpretations.
 * Wisps--and, indeed, many Night Elf units--in Warcraft III.
 * World of Warcraft's Shaman get their power from elemental spirits. How powerful the spirits are can vary from place to place. This has no effect on Shamans in-game of course.
 * The Harvest Sprites and Harvest Goddess in the various Harvest Moon games.
 * The Thief games are rife with nature spirits, from almost literal spirits like the fire elementals, to weird humanoid rat-monkeys and bug beasts.
 * One of the main characters, Viktoria, is a typical dryad / wood nymph.
 * Every nature commune in Lusternia has two nature spirits: a patron animal and an aspect of the earth. Serenwilde has Mother Moon and White Hart (a stag); Glomdoring has Mother Night and Mighty Crow (a crow, obviously); and Ackleberry has Sister Lake and Brother Bear (natch).
 * The Legend of Zelda has a wide variety, most of them helpful to Link (or needing his help):
 * After saving Dragon's Roost island (or that's how you're supposed to do it), Link meets the god of winds, Zehpos, who rewards him with his first melody for the Wind Waker. Later Link meets Zephos' ill-tempered brother, Cyclos.
 * Link of Twilight Princess needs to save the spirits of the Sacred Springs, who guard not only their springs but the regions that the springs feed into.
 * Ocarina of Time features the Great Deku Tree and Lord Jabu-Jabu, who evidently guard the forests and Zora's Fountain, respectively. They make cameo appearances in Wind Waker as well.
 * The Quest for Glory games use this trope several times. There's the Dryad and the forest fairies in the first game, the Guardian of the Heart of the World in the third, and the Leshy in the fourth. Many of these will kill you if you attempt to harm any part of the environment.
 * Several All of the fairies, including Lily White, embody various aspects of nature in Gensokyo.
 * And Yuuka, according to Perfect Memento.
 * The Elementals/Spirits from the World of Mana series. Sprits of the various forms of the life-energy known as Mana. Each one represents a different element, and they usually can be found guarding Cosmic Keystones that personify their elements (Whether that is seeds or stones depends on the game). In the games in which they appear, they are generally responsible for the main character's magic abilities. They include Salamander/Salamando, Undine, Gnome, Djinn/Sylphid, Shade, Wisp/Lumina, Luna, and Dryad. Legend of Mana replaced Luna with Aura, but no other game has done so.
 * Seiken Densetsu 3 also introduced the eight God-Beasts, renamed Benevoldons when they returned in Children of Mana. They also personify the elements, but they have a much more dangerous reputation. When the Mana Stones are broken, they are prophesied to run amok, potentially destroying the world for throwing the balance of nature off-balance.
 * Sakuya in Okami and arguably Amaterasu as well.
 * In Dragon Quest VII, the heroes have to awaken and round up all four Elemental Spirits throughout the course of the game. They can be fought as Bonus Bosses, as well.
 * In "Neverwinter Nights", there is a "Spirit of the Wood" that looks like a white deer.
 * The Sylvari, one of the playable races in Guild Wars 2 are essentially this - a race of plants united by an unconscious Hive Mind who mimic the humanoid form only out of convenience and have an innate ability to manipulate nature, especially other plants.

Web Comics

 * Iri in Wayfarer's Moon gets very unfriendly when people torture those for their own ends.
 * They interact with certain members of the Clan of the Hawk in The Wandering Ones. Some, like First Man and Flame's leafy friends, are benign. However, Coyote also shows up to teach Bobbie and Max, and let's just say he lives up to his reputation.

Western Animation

 * Captain Planet could be seen as a form of this; the show also featured Gaia, who definitely counts.
 * Avatar: The Last Airbender is rife with this. Aang himself, the Avatar of the spirit of the planet, is one of the most powerful. Guest stars include the spirit of a local forest, a river-goddess, and the spirits of the Moon and the Ocean. Let's give them a big hand!
 * And now, in The Legend of Korra, we have Avatar Korra, Aang's reincarnation and the new physical form of the world spirit.
 * Barbie Presents Thumbelina has the tiny Twillerbees, who live in a field of flowers, have the power to make plants grow at an alarming rate, and regularly converse with animals.