Kalidar was the name Blizzard had originally used (on their website) for the island off northwest Kalimdor where Teldrassil was grown. The night elves moved their capital to this island. The Circle of the Ancients and the wise druids pooled their power to create a great tree akin to the World Tree, but on a smaller scale. The tree eventually outgrew the island and the night elves built their city of Darnassus atop it. The island now takes the name of the tree as well, and a twilit forest covers it. Taken directly from the official site: