On January 20, 1997, about 1641 eastern standard time, a Stinson 108, N97108, registered to a private individual, collided with trees while making a forced landing following loss of engine power, at Winter Haven, Florida, while on a Title 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft received substantial damage and the private-rated pilot was not injured. The flight last departed Palmetto, Florida, the same day, about 1610. The pilot stated he was not using carburetor heat as he descended with the engine set at 2,100 rpm. The engine "sputtered" and quit as he descended through 2,000 feet, 2 miles from the Winter Haven Airport. He did not think he could reach the airport and headed for a field. While making a forced landing in the field the aircraft struck trees. Postcrash examination of the aircraft by an FAA inspector showed that each fuel tank contained usable fuel. There was no contamination in the fuel system. After the aircraft was recovered from the crash site, the engine was started and operated normally with no evidence of failure or malfunction. The carburetor heat system operated normally. Carburetor icing probability curves indicate the aircraft was operating in conditions conducive to serious carburetor icing at glide power and visible carburetor icing at glide and cruise power. The curves note that visible icing may become serious after 15 minutes. See Icing Probability Curves attached to this report.