Dryad

"Be still, my princes, I have urgent news from your sisters."

- a Blossom Dryad speaks to Peter and Edmund Pevensie

Dryads were nature spirits closely associated with Narnian trees. During the Creation of Narnia, they came into being shortly after the Talking Beasts, and remained prominent in the country throughout its history.

Description
A number of different words were used to refer to Narnian tree spirts: In addition to "dryads", other terms included "wood nymphs", "wood gods", "wood goddesses", "hamadryads", "tree people", "silvans", or simply "trees". Although these terms were sometimes used interchangeably, the descriptions of tree spirits varied quite widely, so it was not always clear which individuals belonged to which category (if there was any division of categories at all).

These descriptions included dryads who looked more or less humanoid and were connected to individual trees, but also ones who were living, moving trees themselves, with roots and branches functioning as limbs. While there were apparently both male and female dryads, the females appeared to be more prominent (if only because they were mentioned more frequently).

The Magician's Nephew
After Aslan gave animals the gift to speech, he declared to the Narnian creatures; “Be walking trees. Be talking beasts. Be divine waters”. At this command, wood gods and goddesses came out of the trees (though it was not specified if they came out of the trees themselves, or simply out from amongst them). Aslan summoned an oak tree to be a member of his first council.

In later years, some of the female descendants of King Frank and Queen Helen took wood gods as husbands.

The Lion, the Witch, and the Wardrobe
Mr. Tumnus recounted that dryads were among the participants in the nighttime festivals held in Narnia before the usurpation of the White Witch. He also mentioned that some trees were on the Witch's side and worked as her spies,  a point reiterated by Mr. Beaver.

Female tree spirits were among the victims turned into stone by the White Witch and kept in her castle courtyard: These included birch-girls dressed in silver, beech-girls in transparent green, and larch-girls in bright yellow-green (all were later released by Aslan).

Dryads were present at Aslan's camp and served as harpists along with Naiads. Both were later seen running away in fear when the wolf Maugrim came into the camp in an attempt to kill the Pevensies.

When her other wolf brought the news that Maugrim had been killed and urged her to retreat, the Witch refused and ordered him to summon all the creatures on their side, including the spirits of the trees. These evil tree spirts were later present during the sacrifice of Aslan on the Stone Table.

During their reign, the Pevensies enacted laws that prevented good trees from unnecessarily cut down.

The Horse and his Boy
While in Tashbaan, Tumnus reminded Shasta (whom he believed to be Prince Corin) that he had promised to come and stay with Tumnus for a week during the Summer Festival in Narnia, where there would be all-night dances with the fauns and dryads.

Prince Caspian
When Narnia was invaded by the Telmarines, they began to cut down trees, resulting in the dryads falling asleep within their trees for centuries. Lucy Pevensie saw them waking and dancing sleepily, shifting back and forth from treeish to human-like form; this happened because Aslan was nearby in the clearing. Some time later they were fully awakened by Aslan and dance about him, Lucy, and Susan Pevensie, paying adoration to Aslan by crying out his name. Bacchus, Silenus and his donkey, and the Maenads joined in the dancing.

The next day they set off to Aslan's How, and during the battle that ensued, they swooped in on the Telmarines, using the branches and roots of their trees to swing them around, strangle them, and destroy their weapons. During the celebration of the Old Narnians victory, different types of soils were dug up for them to eat. Some Holly dryads were mentioned drinking wine, and they became very chatty.

The Voyage of the Dawn Treader
Reepicheep told of a dryad singing him the verse for the Utter East while he was still in his cradle.

The Silver Chair
A dryad maiden with willowy-looking hair was mentioned looking after Jill during her stay at Cair Paravel. After Jill, Eustace, Puddleglum and Rilian escaped the Underland, dryads were seen performing the Snow Dance with fauns, dwarfs and other woodland animals.

The Last Battle
A beech dryad left her tree and warned King Tirian of how the trees in Lantern Waste were being felled by Calormene, and the dryads were being slain. She then fell down, died, and vanished into thin air because her tree had been chopped down

Green Dryad
While not actually being green, this dryad was actually made of Blossoms from a cherry tree. Her gender is most likely female as she has long hair and the pink blossoms show to be a more feminine kind of tree. The tree is located on the banks of River Beruna just outside Aslan's camp, who greeted Lucy on her arrival to the camp. She has made an appearance in both the LWW and in the PC movie, when she was in a dream that Lucy had. She was voiced by Katrina Browne. She might have been cast as "Green Dryad" because the dryads were originally going to be actresses in green dresses, makeup and hair. She was one of the many dryads and hamadryads who told the residents of Aslan's camp of his death.

Beech Dryad
A dryad lives in the beech tree that neighbours the cherry tree. She also greeted Lucy on her arrival, and was also a dryad who told the residents of the camp of Aslan's death. She had a minor role and said nothing more in the LWW movie.

Mr. Tumnus told Lucy of evil dryads who were on the witch's side in the area known as 'Allies Enclave'. Also, Cherry trees can be seen coming into bloom after the scene in which the Pevensies nearly drown but escape the river. Dryads most likely lived in the cherry trees.

Trivia

 * Evil Dryads were seen in the concept art of the Disney version of The Lion, the Witch, and the Wardrobe, but were not seen. (They were, however, mentioned).
 * Lewis describes the dryads of Narnia as having specific characteristic features of each kind of tree an individual dryad is bound to (beech dryads as queenly, gracious, and goddess-like, birch dryads as slender, graceful, and limber, oak dryads as wizardly and elderly looking, etc.), wearing clothes matching the colors of the bark or foliage of their respective trees (beech dryads wearing fresh transparent green, birch dryads wearing silver, and larch dryads wearing green so bright it looked almost yellow), and having leaves growing their heads. He also describes them has being able to move with their trees and cause their trees to take on their human-like appearances.
 * In the films however, dryads are portrayed as non-physical spirits who use leaves and flower petals to form and solidify their bodies, and when they are possessing their trees to move, their trees do not take humanish features (except for one moment when a tree is killed with a boulder, it makes the face of a person crying out in agony within its foliage) when it dies, they also have the ability to move and stretch out their roots like tentacles when fighting the Telmarines.
 * In a deleted scene from the second film, Prince Caspian, a dryad is shown forming and coming out towards the Pevensies and Trumpkin, but dies because his tree miles away was cut down. It is curious to note that when the dryad died, its leaves exploded rather than falling on the ground dead, and slowly fading into thin air.
 * In the Prince Caspian (book); a wicked Telmarine man, who was beating a boy with a stick, was turned into a tree by Aslan. Whether this means he was turned into a Dryad, or just a simple ordinary tree, is unknown.
 * Originally, the dryads in the first film were intended to be physical beings, played by actresses in costumes with green, leafy hair, pale green skin, and garments made of foliage. This design was filmed for a dancing scene at Cair Paravel at the end of the movie, but was discarded. Scenes of these dryads can be seen in behind the scenes features of the DVDs, one of the trailers for the movie, and as a cameo in the coronation scene at Cair Paravel.