The airplane was on the final approach leg of the traffic pattern to the turf runway. The private pilot recalled that the airplane was at an altitude of 800 ft above ground level and aligned with the runway, but he had no further recollection of the flight. A witness observed the airplane flying "low and slow" about 20 feet above the ground when the nose pitched upward, the airplane "stalled," and the left wing struck the ground. The owner of the airport stated that the trees at the approach end of the runway were damaged, and broken branches were found scattered at the base of the trees immediately after the accident. The fuselage and wings sustained substantial damage consistent with collision with trees and terrain. The pilot stated there were no preaccident mechanical malfunctions or failures with the airplane during the flight that would have precluded normal operation.