The pilot was engaged in mustering cattle out of thick undergrowth. As he was moving the helicopter slowly forward, while checking the undergrowth for any remaining cattle, the main rotor moved under the overhanging branch of a large tree. The pilot attempted to move the helicopter down and to the right but the main rotor struck the overhanging branch. The helicopter impacted the ground and caught fire. The tree trunk was camouflaged by rubber vine, which constituted much of the undergrowth and probably reduced the pilot's awareness of the proximity of the tree.