The pilot was conducting cattle mustering operations. Weather conditions at the time were very hot, with a 10 to 15 knot wind. The pilot advised that while flying downwind at 30 knots and 80 feet above the ground, he commenced a pedal turn to the right. After some 90 degrees the turn suddenly stopped and the aircraft sank rapidly to about 35 feet above the ground. The main and tail rotors struck trees, but the pilot was able to maintain control and fly the helicopter to a clear area, where a safe landing was made. No defect was found with the helicopter or its systems which may have contributed to the occurrence and the reason for the loss of control, reported by the pilot, was not determined. This accident was not the subject of an on-site investigation.