A drive mechanism for a tree harvester including a frame movably mounted on a vehicle, the drive mechanism being secured to the frame along with delimbing and shear assemblies arranged on opposite sides of the drive mechanism, the drive mechanism comprising an endless track trained about a drive sprocket and rollers, the rollers supporting a portion of the track in alignment with the delimbing assembly, grapples being operable to secure a tree in driven engagement with the supported track portion while permitting the tree to be axially moved relative to the delimbing assembly and shear assembly for processing.