Brachiation( Masters of the Wild: A Guidebook to Barbarians, Druids, and Rangers, p. 21)
You move through trees like a monkey.
Climb 6 ranks,
You move through trees at your normal land speed by using your arms to swing from one branch to another. To allow brachiation, the area through which you are moving must be at least lightly wooded, with trees no farther apart than 15 feet. You may not use this ability while holding an item in either hand, or while wearing armor heavier than medium.