While on the takeoff roll from a stop-and-go landing, the flight instructor scanned the instruments and noticed that the airspeed indicator was at zero. He perceived that the engine was producing full power and that the airplane had “enough lift” but the airspeed needle was not moving. He considered aborting the takeoff but determined there was insufficient runway to stop. The airspeed needle began to move, and the flight instructor rotated the airplane for takeoff. The airplane would not climb, so he banked the airplane to maneuver around trees at the end of the runway. The airplane collided with the trees which resulted in substantial damage to the wing and fuselage. The flight instructor indicated that there were no mechanical malfunctions that contributed to the accident. The flight instructor indicated that they started the takeoff roll with about 1,300 ft of runway. Airfield information put 63 ft trees 500 ft from the end of the runway. Performance calculations revealed that to clear a 50 ft obstacle, a 2,000 ft takeoff distance was required.