The pilot was engaged in mustering operations at 100 feet above ground level and at 60 knots airspeed, when he heard a noise from the rear of the aircraft. He observed the rpm indicators split, with the engine rpm showing an overspeed, and he assumed a clutch cable failure. The aircraft was placed in an autorotational descent. As there was no clear landing area immediately available the pilot turned the aircraft into wind and attempted to find a clear area amongst the trees. The aircraft hit a tree, however, fell to the ground and rolled onto its side. The drive to the main rotors had become disconnected because the cable to the belt drive clutch control tension spring assembly had failed inside the assembly. The cable had been inspected for defects, and none were detected, at the last periodic inspection which occurred 59 hours prior to the accident. The cause of the cable failure could not be determined. The cable had been in service for 2210 hours. It is an "on condition" item, which does not have a specified life. The maintenance system for the aircraft requires that the cable be removed and inspected each 400 hours time in service. Removal is required to inspect the area on the cable that failed. The cable is inspected in situ each 50 hours time in service. The altitude and speed selected by the pilot gave sufficient performance potential for a safe autorotational landing, but the low cruise height significantly reduced the time available to locate and establish an approach into any suitable landing area.