AT APPROX 200 FEET AGL, UPON COMPLETION OF A PRACTICE FORCED LANDING PROCEDURE, CARBURETOR HEAT WAS DE-SELECTED, FULL THROTTLE APPLIED AND THE FLAP SETTING REDUCED FROM 40 DEG TO 20 DEG. ACCORDING TO THE CFI, THE ENGINE DID NOT DEVELOP FULL POWER WITH THE RPM OBSERVED TO BE 2100 VICE 2700 RPM AT RATED POWER. THE AIRPLANE CONTINUED ON THE SAME HEADING, CROSSED OVER A WOODED AREA BARELY CLEARING THE TREES, AND SETTLED IN A NOSE-HIGH, CONTROLLED ATTITUDE, INTO THE TREES FOLLOWED BY GROUND CONTACT. EXAMINATION AT THE CRASH SITE REVEALED THAT THE CARBURETOR HEAT VALVE OPERATED NORMALLY, THE ENGINE SPARK PLUGS AND EXHAUST STACKS WERE FREE FROM MAJOR DEPOSITS AND THAT THE OUTBOARD TIPS OF THE PROPELLER BLADES WERE BENT OPPOSITE TO THE DIRECTION OF ROTATION. A FOUR INCH DIAMETER OAK LIMB HAD BEEN SLASHED BY THE PROPELLER.