According to the pilot, while flying at a low altitude, the engine lost all power. In an effort to restore power, he rotated the fuel selector to what he thought was the left fuel tank while focusing his attention outside the airplane to conduct an emergency descent and landing. During the emergency landing the airplane impacted trees sustaining substantial damage to the wings, lift struts, fuselage and right elevator. A post-accident wreckage examination which included an engine run revealed no mechanical failures or malfunctions with the airplane that would have precluded normal operation. In addition, fuel was found in the left main fuel tank, no fuel in the right main fuel tank and the fuel selector was in the off position. The pilot stated that he must have inadvertently selected the fuel selector to the off position following the loss of power.