Trees as a major theme in fantastic literature

No one could list all the times when trees were important in fiction. If they could, no one would read it. There are too many. I certainly can't do it comprehensively for fantastic literature, either. However, here's a list.

I confess--this isn't going to be scholarly. I'm not going to go back and look up or read anything before I post this. Shame on me. Here are some important trees in works of fiction, from some of my favorite authors, as I remember them:

J. R. R. Tolkien
Tree and Leaf
in the Silmarillion, two trees were the source of light for all the world.
In The Lord of the Rings, there were:
the party tree at Bilbo's good-bye party
Old Man Willow, and the old forest
the holly trees engraved on the gate of Moria.
In the realm of Galadriel and Celeborn, the elves lived in harmony with the trees, and on them.
Saruman cut down trees.
the ents were sentient, intelligent trees, and they lived in a great forest, Fangorn.
the white tree of Gondor was a symbol of the kingship
Sam planted a seed from Galadriel to replace the party tree, as one of the symbols of the restoration of the Shire.

C. S. Lewis, in the Narnia books
The wardrobe was made from a tree.
Digory got a fruit from a tree for his mother.
Apparently both of the above had some connection to the Tree of Life

Jack Vance
Ramus Ymph becomes a tree as punishment in Maske: Thaery. Vance doesn't say much about trees throughout his writing.

Urusula K. Le Guin
the Immanent Grove on Roke is the center of Earthsea
She wrote The Word for World is Forest

Patricia McKillip
In the Hed trilogy, the wizards can become trees.
Morgon becomes one, also.
In the Forests of Serre, The Book of Atrix Wolfe, and Winter Rose use forests as the setting for significant sections of the books.

Elizabeth Haydon
As I recall, she had a root of a giant tree going under the world, and also acting as a passage through time, in her trilogy.

A. A. Milne
Pooh, Piglet, and Owl (Wol) all lived in hollow trees, or in hollows in trees.

Robert Silverberg
Majipoor has many kinds of trees described, some quite bizarre. The Piurivars live in a dense forest.

Sharon Shinn
Forests provide the setting for some of her writing, for example in Summers at Castle Auburn. They don't in the Samaria books. The Shape-Changers Wife is a tree.

Dan Simmons
The Templars used giant trees as spaceships in the Hyperion series. I believe there were tree-planets, also.

Connie Willis and Gene Wolfe
I can't think of any particular tree use by either of them.

See the end of this post for some of the reasons for the use of trees as symbols in literature. I wouldn't say that they are symbols in all of the above. In a lot of those stories, they are just trees.

Please use your comments to add to (or subtract from) this list.