IMPROPER PREFLIGHT PREPARATION BY THE PILOT BY TAKING OFF WITH THE FLAPS EXTENDED, WHICH RESULTED IN AN INADEQUATE RATE OF CLIMB TO CLEAR OBSTRUCTIONS BEYOND THE END OF THE RUNWAY, AND THE PILOT'S DELAY IN ABORTING THE TAKEOFF AND HIS FAILURE IN MAINTAINING AIRSPEED, WHICH REDUCED HIS ABILITY TO FLARE THE AIRCRAFT. THE HIGH OBSTRUCTIONS (TREES) NEAR THE END OF THE RUNWAY WERE CONSIDERED TO BE A FACTOR.