The helicopter pilot reported that he was landing on a pad in a confined area. He added that, as he approached the landing pad, he slowed the helicopter to transition to a hover. The main rotor rpm began to drop, and he applied full throttle, but the rpm continued to decline. The helicopter was unable to maintain altitude and slowly settled into the trees on the hillside about 20 ft short of the landing pad. Subsequently, the helicopter struck the trees and rolled onto its right side. The helicopter sustained substantial damage to the fuselage and main rotor system. The pilot reported that there were no preaccident mechanical failures or malfunctions with the helicopter that would have precluded normal operation. The pilot reported that, after the accident, he noticed there was a significant right quartering tailwind, which required the application of more left pedal than anticipated. He further explained that the increased application of antitorque pedal lessened the available power to maintain the main rotor rpm. He concluded that the approach could have been completed safely with a steeper and faster approach to better manage engine power.