PLT EXECUTED AN EMERGENCY LANDING INTO TREES AFTER HE EXPERIENCED AN INFLIGHT FIRE AND ENG FAILURE SHORTLY AFTER T/O. THE LNDG IN THE TREES WAS EXECUTED AFTER THE PLT DECIDED THAT HE COULD NOT MAKE IT TO A CLEAR AREA. INVESTIGATION REVEALED THAT THE FIRE HAD INITIATED IN THE AREA OF THE MUFFLER AND CARBURETOR. EXAMINATION OF THE MUFFLER REVEALED THAT IT HAD WRINKLED AND CRACKED AS A RESULT OF SEVERE OXIDATION AND NORMAL HEAT EXPANSION. ANALYSIS OF THE EXHAUST DEPOSITS ON THE CRACK SURFACES AND THE EXTERIOR SKIN OF THE MUFFLER INDICATED THAT THE MUFFLER HAD BEEN CRACKED FOR SOME TIME PRIOR TO THE ACCIDENT. THE ACFT HAD RECEIVED AN ANNUAL 278 HRS PRIOR TO THE ACCIDENT, BUT HAD NOT BEEN INSPECTED FOR THE 3 YRS PRIOR TO THE LAST INSPECTION. THERE WERE NO RECORDS SHOWING WHERE THE MUFFLER HAD EVER BEEN OVERHAULED OR REPLACED DURING THE ACFT'S 2,650 HR HISTORY. MFGR RECOMMENDS MUFFLER REPLACEMENT EVERY 1,000 HRS.