Those creatures that some would call “elves” but in reality are of fey-blood, spawned by the Great Tree in opposition to Lilith’s creation of the Vampire Tree, which birthed those called upir, or “vampires”.
Fey who have not forsaken their magic (see Choosing Mortality) are able to “join with the forest” by transforming themselves into trees: these are the Whispering Trees.
The trees are so named because when the wind passes through a grove of Whispering Trees you can hear the voices of the fey; speaking warnings, or riddles. If one places their hand against the bark of such a tree, it is possible to hear the voice of the fey who chose to transform themselves (it is possible this relies on the psychic ability of the individual touching the tree, though this is yet to be confirmed).
It is not unheard of for Whispering Trees to grant pieces of themselves to those who carry heroic blood, usually for the forging of weapons. These weapons are imbued with something of the spirit of the tree, often creating weapons of considerable power–especially against upir.
Michael Scott Hand 