The airport manager said the airplane began its takeoff on the 2,500-foot-long runway 13 from the displaced threshold, which is 400 feet from the approach end of the runway. The pilot said he rotated at 55 knots and the airplane lifted off the runway but would not climb. Almost immediately, the stall warning horn began to sound and he lowered the nose to gain speed. The airplane then settled back onto the runway. The pilot reduced the power and began applying brakes to abort the takeoff. The airplane overran the end of the runway, went down a hillside, and collided with trees about 600 feet from the runway. The pilot reported there were no mechanical malfunctions or failures.